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Ask Tadge Post your questions here for Corvette's Chief Engineer Tadge Juechter and then discuss the questions and his answers.

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Old 03-28-2015, 07:39 AM
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Default Ask Tadge: Answer Thread

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Old 03-28-2015, 07:40 AM
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Default Corvettes and Longer Warranties

Original answer thread is here.

jvp asked

Have you considered further differentiating the Corvette from the rest of the Chevy brand, by perhaps extending the bumper-to-bumper warranty another year and/or 12,000 miles? Perhaps make it on a par with Cadillac’s warranty?
Tadge answered

Compared to other high performance cars. the Corvette is already has much lower operating costs, and a very competitive warranty, Our standard warranty includes:
  • Scheduled maintenance for two years or 24,000 miles
  • Bumper to bumper warranty for three years or 36,000 miles
  • Powertrain warranty for five years or 100,000 miles
In addition to the organizational impracticality of having a very different Corvette warranty than other Chevy products, it's important to note that there's a lot of fine print associated with auto warranties. Some manufacturers have impressive headlines, but when you read the fine print you see much content is excluded from coverage, or the warranty is void if you use the car on the track. We are especially proud to say when Chevrolet certifies a car for track performance, we stand behind the warranty - even the 100,000 mile powertrain warranty - even for track use.

Also, I can assure you that we do not design any product to just live through the warranty period. We do our best to design vehicles that last as long as practical. We know some Corvettes have been on the road for over 60 years, and we would like the cars we are building today to be driving around in 2075!

Tadge Juechter
Chief Engineer - Corvette

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Old 03-28-2015, 07:41 AM
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Default

Original answer thread is here.

jdvann asked

By now everyone knows there are some critical components that are now unavailable for the 97-2000 model cars, specifically the EBCTM(Brake Control Module) and the Steering Wheel Position Sensor. Is there anything GM can do to make a run of these rare parts? Or convince someone in the aftermarket too? One other option to explore here is to provide a way to update the obsolete components to the newer system?

Thanks in advance.
Tadge answered

I have been personally involved with a number of customers (and GM employee owners - no, there is no special stash of parts we keep for ourselves!) and the challenges they have had finding replacement parts, particularly electronic components. The auto industry is unusual compared to most consumer products in that we have longer warranties and maintain replacement part inventories far, far longer than other products. My home is filled with products I have loved but are rendered useless because I can't get a replacement part. I have an expensive Canon SLR camera that doesn't work because the power switch broke and is unavailable. My beloved stereo receiver sits useless in the basement because the transformer blew and I can't get another. Ditto a 5 year old computer, a 2 year old microwave oven and lots of other stuff! I know this doesn't compare to a Corvette, but I have great empathy for folks trying to keep their cars in perfect working order and understand how frustrating it can be when one small part can't be replaced.

As a company we attempt to maintain parts availability for 10 years after the last production use of a particular part. So as a car goes out of production, our service department looks to see which parts will continue in production vs which will no longer be used by other cars. For those that are going out of production, based on our replacement history, an estimate is made on what the ongoing demand will be for that part. We try to be conservative and err on the side of a bigger inventory. We then make a "lifetime buy" of those components to stockpile in inventory. GM pays for all of the parts upfront, then pays for individual packaging and the warehousing costs until all the parts are sold. For many parts the inventory is never sold out and it is a big loss for us. That is why we can't afford to buy 20, 30 or more years of inventory. Also, parts deteriorate with time even when properly stored so they have a finite "shelf life" and eventually have to be scrapped. Sometimes the demand for the parts exceeds our estimate and the inventory is depleted in less than our 10 year goal. Some people, realizing a part is becoming scarce, will buy up our inventory of parts hoping to resell them at exorbitant prices.

I know some of the C5 electronic components are very scarce. I have personally inquired as to what it would take to do another production run to supply the market. We, GM, are more than willing to share the technical information we own to enable any willing supplier to go into the business of producing those parts. For electronics, which evolve very fast, this turns out to be impossible. No one makes some of the individual components anymore, the supplier with the knowledge of how to do it has gone out of business. Even if they were in business, the parts were made on expensive machinery that is no longer available controlled by software written in a language no one uses today. The startup costs to recreate a 1990's electronics assembly process would be astronomical and there would be no way to recoup those costs through the resulting parts sales (each part would have to cost more than the car is worth). So, no, we haven't been able to convince anyone in the aftermarket to take it on.

OK, why don't we engineer new solutions that use modern components to solve the problem? Well, that too would be enormously expensive and filled with uncertainty. We have our hands full engineering cars that work well for years with all new parts. Re-engineering a new part to be compatible with a variety of old parts in unknown conditions would be unreliable and economically impractical. Also, where do we draw the line? Should we stop at C5? Or should we go back to C4? C3? There are few engineers and little documentation still existing that would give us a starting point for such an effort. We count on the aftermarket to supply vintage parts. Where there is a good market opportunity, you see a healthy supply, where the economics are nonviable, the parts get scarce. I have many friends in the Corvette community who are facing this challenge. Trust me, If I could do something to fix it I would have already done it.

The one good thing that has come out for this experience on Corvette is that, going forward, we are going to take a closer look at parts that are hard to replicate and a have long shelf life. For those special parts, we will plan for a longer inventory horizon than 10 years.

Tadge

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Old 03-28-2015, 07:46 AM
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Default C6 Z06 Question for Tadge Juechter

Original answer thread is here.

AZDANZ06 asked:

I am writing to you on behalf of all C6 Z06 Owners here at the Corvette Forum. There has been way too many C6 Z06 owners that have suffered LS7 engine failures due to dropped valves. GM claims that there was a manufacturing problem that was subsequently corrected, yet engines and off the shelf replacement cylinder heads produced after that date are also failing at an alarming rate. Loyal owners of even extremely low mileage vehicles are continuing to measure valve-to-guide clearances far beyond service limits and have had their heads reworked at a significant cost. This is evidenced by a cross section of Corvette Forum Members who have had their valve-to-guide clearances measured, 88% of the 208 member cars checked have had out of spec valve guides on C6 Z06's built from 2006 through 2013. With the apparent widespread incidence of excessive valve guide wear among LS7's, does GM know anything regarding the root cause of the issue and/or potential mitigation actions in order for LS7 owners to regain confidence in the platform and to retain loyal GM Customers?
Tadge answered:

First of all, let me explain why it is taking longer to answer this question than the usual week. It is my intention to use this part of the forum to get the best, most accurate information to the Corvette community I can. Some questions, like this one, require a number of internal experts be consulted for a complete answer and so it takes longer for everyone to weigh in.

I purchased a 2006 Z06 myself. It was my pride and joy. I sold it a couple years ago in anticipation of buying a C7. I sold it to Damian Zink, who works in Bowling Green and is continuing to use it on road and track. I’m very happy it is still in the Corvette team family. I tell you this to counter a prevailing assumption on the forum and elsewhere that we on the Corvette team only care about selling new cars. Nothing could be farther from the truth. Many of us are customers ourselves, our friends and families own a lot of cars from many generations and we have long term relationships with many of our customers. The long term ownership experience is very important to us – even well beyond the warranty period.

Engine reliability is a huge focus for us and we have been monitoring the LS7 since it was introduced. We will continue to do so for the foreseeable future. I can promise any learning we have will be incorporated into our future designs and we will make every attempt to treat customers fairly.

The description of the LS7 experience below is being provided by my counterpart on the engine side, Jordan Lee, the Small block Chief Engineer:

The LS7 engine is a high performance engine, our highest output naturally aspirated engine in production today. It achieves its power output by incorporating very large titanium intake valves and a very aggressive camshaft profile. As a result, the LS7 does exhibit more valve train noise than our other Small Block variants. The large valves and the rapid open and closing events of the valves will result in valve train tick. All LS7 engines exhibit this valve train noise. The cylinder head is also quite unique compared to our other Small Block variants. The head is CNC machined, including the ports, by one of our reputable suppliers. They fully machine the cylinder head, including the valve guide ID, then they assemble the head with valves and springs and deliver the fully assembled cylinder head to our engine assembly plant.

Like all manufacturers, we have specifications and tolerances for all critical dimensions including the valve guide ID. Unfortunately for a 9 month period of time, from July 2008 to March 2009 we have evidence that some cylinder heads (a small percentage of the total population) were delivered to our assembly plant with valve guide ID’s that were out of specification and were over-sized. This resulted in more valve train noise than is normal. Once the “out of specification” condition of the valve guide ID was identified, we worked with our dealerships to repair customer cars when we identified engines that had out of specification cylinder heads. For the 2009 MY we replaced a total of 65 cylinder heads (Z06 production was 1654 cars and most heads were replaced in pairs so roughly 33 engines). Due to this valve guide ID issue, our cylinder head supplier implemented more rigorous inspections and quality check procedures to ensure they made and shipped only cylinder heads that are within specification. After the time period in question the number of customer complaints dropped significantly.

One issue we struggled with was defining an inspection procedure that the dealership can perform to determine if the guides are out of spec. The only accurate method to measure valve guide ID is to remove the head from the engine, remove the valves, and use a dial-bore gauge or CMM (Coordinate Measuring Machine) to accurately measure the ID. This method requires a lot of disassembly of the engine and many customers don’t want the heads removed for inspection. As a result, we developed another technique fondly known as the “wiggle method” where the valve spring is removed and the valve is wiggled in the guide, and the distance is measured with a dial indicator and then using trigonometry the clearance is calculated. Unfortunately this method is not very accurate and has a tendency to indicate a larger guide internal diameter than it actually is. We know this for a fact because we tested the method by using the wiggle method on a few cylinder heads and then disassembled the heads and measured them on a CMM (Coordinate Measuring Machine) for an accurate measurement and then compared the results between the two techniques. We’re currently investigating other techniques to get a better measurement without disassembling the cylinder heads and will instruct our dealerships accordingly if we are able to develop one. To date we have not been successful in developing an accurate non-intrusive technique. Since there is significant error in the wiggle method we are contemplating whether we should continue with this method.

Regarding valve guide material, the LS7 uses a premium guide material, Federal Mogul PMF10 which is oil impregnated and has a high moly content. We look at our warranty claim data almost daily looking for trends and problems and do act as quickly as possible to make sure our customers are taken care of and we fix any known problems ASAP. Based on the data we’ve amassed to date, it still appears that our suspect period is July 2008 to March 2009. Worth noting is that most of the heads made in this time frame are indeed within specification. We stand behind our products and our customers, and will repair under warranty any cylinder heads whose guides are indeed out of specification within the Powertrain warranty period.
Tadge added:

Jordan and I are very disheartened at the response to our answer on the LS7. I made the point that we care a great deal about the long term ownership experience for our customers, but few on this thread of the Forum seem to believe it. Of course we have read the testimony of the participants and want to continue the dialog assuming it can be done in a constructive way.

Some of the posts imply that having our cylinder head supplier inspect cylinder head valve guide inner diameter dimensions is not evidence of "good process control", it actually is when dealing with low volume production. Inspecting 100% of the cylinder heads manufactured does provide assurance that the parts are indeed within specification. The supplier doesn’t' want to scrap a lot of heads, so they will also implement excellent process control to assure they are consistently making good parts, and the 100% inspection is final assurance all is well before shipping parts.

Most troubling to us is the massive discrepancy between what our internal data sources are telling us and the evidence being discussed on the thread. We have our warranty data and detailed break down and technical analysis of parts returned after warranty replacement. We also have the process control data from our head supplier - This includes very fine measurements of valve guide with high quality instrumentation. We also have data on wear rates from measuring new and fully tested engines(Including fairly recent data testing the Camaro Z/28) Our data show that the number of engines in the field with out of spec guides should be very small. Although it is hard to tell exactly from the claims on the thread, it appears that most of the measurements proving the valve guides are oversized come from aftermarket performance shops who make a living from repairing, reworking and tuning cylinder heads. It appears there is something different about the way they are measuring vs the way we are doing it. So our next step to try to find the truth is to contact several of the shops mentioned in the responses and consult with them on how their work is being performed. There is no doubt some of them are excellent facilities so maybe we can learn something from each other.

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Old 03-28-2015, 07:48 AM
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Default Car overheating issues on track

Original answer thread is here.

lawdogg149 asked:

Could you describe what occurred to the car that the media ran at road atlanta back in November 2014. It seems several magazines have quoted having the over heating issue but no one clarified if it was the trans or the engine oil. I know from my personal experience that my car did get pretty warm on a cold 40 degree day there a few weeks back. I and many people are concerned we will see issues come this summer without mods.
Tadge answered:

There are lots of interesting back stories behind recent media tests, but the question asks about Road Atlanta so for the purposes of this thread I will focus on our long lead media event last November. We spent a week there with journalists from around the world. We had pro drivers Tommy Milner, Randy Pobst, and Andy Pilgrim behind the wheel along with many other very capable drivers. They were permitted to run consecutive laps with minimal or no traffic, so essentially "qualifying laps". Over the course of the week we had 2 cars come into the pits with a hot warning messages. The first was due to the loss of an accessory drive belt. We had a pre-production tensioner on that car which failed, throwing the belt and we lost the water pump. We have had no issues with production tensioners. The second car was an automatic. I believe it was being driven by Randy on the hottest day there which was right around our design performance target of 86 degrees (more on that below). After multiple laps at speed he came in with a hot warning message. Although the car had been out on track all week, that was the first and only incident. In Corvette's 60 year history, we have never put automatics on track for media and never encouraged people interested in track usage to buy automatics. The new 8 speed automatic gives us a chance to put more automatic transmission customers on the track. Since there is some lack of clarity around the true capability of each of the transmissions, this question gives us the opportunity to publish some guidelines:
  • The Z06 Manual is designed to keep engine oil, coolant, transmission and differential fluids below the hot warning targets when driven by a professional on a 30C day (86F) on a "typical" racetrack for an indefinite period of time (effectively the time to burn through a full tank of fuel). Our team validates the durability of the Z06 cooling systems with a 24hr accumulated track test to simulate the most aggressive track-day usage by our customers.
  • We designate our track: the Milford Road Course, as the "typical" standard, but recognize that there are tracks around the world which are easier on a cooling system and some which are harder on a cooling system. Generally speaking, tighter tracks with lower average speed and higher sustained RPM, will drive higher fluid system temperatures.
  • Higher temperature ambient conditions affects all car's abilities to run sustained laps at ten-tenths.
  • The Z06 Automatic transmission put in "Drive" selects the lowest possible gear ratio for best acceleration, and because it has 8 closely-spaced ratios typically runs higher average RPM than the manual. This optimizes lap time performance, but also taxes the engine oil and coolant more for any given track. So the automatic has the capability to run faster laps than the manual, but thermal limitations are reached more quickly. Customers who are planning to run extended track-day sessions at 'professional' speeds, are advised to go with the manual transmission, or to paddle shift the automatic and select higher gears when conditions warrant it.
  • Any time the maximum recommended temperatures are reached in any condition, the DIC will give warnings at the appropriate time for coolant, oil, or transmission fluid. A cool-down lap or two will bring operating temperatures back to a reasonable level and aggressive track driving can be resumed.

Some may wonder why don't we design to higher temperatures, say 110 degrees, to accommodate southern tracks in the Summer. We have used the "pro driver at 86 degrees" criteria for generations of Corvettes and for the vast majority of customers, it has resulted in excellent performance for their usage. If we designed to higher temperature criteria, we would have to add a lot of cooling hardware which drives mass up and perhaps more importantly, you have to feed the system with more air which has a huge impact on appearance and aerodynamic drag. Like most aspects of car design, the challenge is in finding the best balance of conflicting requirements.

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Old 03-28-2015, 07:50 AM
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Default Motor Trend 2015 Z06 vs. 2015 GT-R Nismo

Original answer thread is here.

Bwright asked:

You mentioned in this week's answer to the Ask Tadge question on overheating that there are, "Lots of interesting back stories behind recent media tests." In light of that, what are your thoughts on the recent Motor Trend test of the new Z06 vs. the GT-R Nismo at Willow Springs? Any interesting back stories on that or any other recent media tests?
Tadge answered:

To be perfectly honest, both Chevrolet and Motor Trend were surprised by the test results - both the lap times achieved and the subjective comments on handling which did not match their impressions from the first drive story at Road Atlanta. Obviously the GT-R Nismo is a supremely capable machine engineered for precisely this kind of track work, so nothing against them, but we thought we would do better. After the story was published, we decided to examine that car closely and do a follow up test at Willow Springs.

We first discovered an alignment setting error in the rear. We knew something was wrong with their test car because of Randy's oversteer comments. In the words of our development engineer, Jim Mero, "The car is tuned for a small amount of understeer, but we found out the rear caster was inadvertently set to 2 degrees instead of 0 degrees. This causes ride and roll oversteer". We try to keep the Corvettes used for media tests in perfect condition, but didn't this time, and the alignment clearly had an effect on handling and driver confidence.

We also learned the Nissan was using octane booster, as it will cut power when running the 91 octane pump fuel available locally. Generally speaking, higher octane enables more aggressive spark calibration and higher power. While the Z06 is certified for 91 octane fuel, adding octane boost will offer greater resistance to spark retard and detonation under thermally challenging conditions (reduced likelihood of power reduction when intake temps go up). Racing fuel (100 octane) available at the track improves this robustness even further. We will be recommending that customers who track their car, especially at higher temps, use the highest octane fuel available.

Although we do track testing at quite a number of tracks around the country, we never tested at Willow Springs, so we decided to rent the track and check the performance of the Z06 ourselves. We looked at it as an opportunity to learn something. What Randy told us and we confirmed is that the track has an unusual combination of speed and roughness.

We used exactly the same car Motor Trend tested, as well as a second car, an 8 speed automatic. With proper suspension alignment, we saw a marked improvement in handling.

We also used the opportunity to tweak the calibration of the magnetic ride dampers in Track mode (Tour and Sport modes unchanged), and were able to improve the vehicle’s dynamic behavior. Since we think that calibration is uniquely suited to very rough tracks, our plan is to offer it through our Performance Parts department for customers who frequent those types of venues. So it was a good exercise for us.

We invited Motor Trend to test the car again with suspension alignments corrected and give us feedback on the new calibration. They are planning a follow up article based on Randy's experience, and since we don't want to "scoop" their story I won’t say specifically what the results were. However, I can say we were very satisfied. Look for it soon!
Tadge wrote:

Maybe I should have said we invited Motor Trend to "drive" the car again instead of "test" again. They didn't agree to a full test (or guarantee any write-up for that matter). In fact, they wedged our 2 (manual and auto) cars into an already scheduled test. They actually told us that the day was already full. We had 1 shot at Randy driving, so we left the cars the way we will now recommend our customers configure them for a track like Willow Springs, - correct alignment and new shock cal.

We are moving forward with offering the "rough track" cal as a performance part. We will also check at other tracks to see if the "rough track" cal should be what we put in the car from the factory. However based on everything we've done to date, we feel the new calibration will be exclusively for rough tracks and the calibration we are currently building the cars with will be optimal for 95% tracks in the USA.

As the gap between the race car and the production car closes more now than ever, we realize we need to adapt the strategy used for the Corvette race cars. The race cars would never use the same set up for Sebring as they do for Road Atlanta, or VIR. The "one size fits all" calibrations of a vehicle like the Z06 would have to be compromised if we chose to address extreme conditions on a small amount of tracks. In the future if we were to experience a dynamic phenomena's at tracks that we feel strongly will enhance our customers driving experience at that track or a very similar track, we might include another calibration as a performance part. Think of it as an "app" for your car. Our objective of keeping our valued customers best interest in mind has never changed. Offering these options is an example of that.

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Old 03-28-2015, 07:52 AM
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Default Nurburgring and the C7 Z06

Original answer thread is here.

jvp asked:

There’s a lot of curiosity here and elsewhere as to what exactly happened with the yellow C7 Z06 at the N’Ring during your autumn visit. Do you have the data to know for sure, and can you share the details with us? I assume Mero's OK?
Tadge answered:

Since I wasn’t there and Jim was, I asked him to answer this week’s question. He goes beyond a narrow answer to the question, but some readers will be interested in more detail of what we do when we go to the Ring. Although fast laps get the headlines, the vast majority of our work there is related to tuning, testing and validation:

Jim Mero adds:
Although the day we hit the guard rail was almost 7 months ago it seems like it was yesterday.

As much as I’d like to have a super-cool story such as: the picture shown online was taken after we were airborne at 160 mph flipped 3 times and hit the Armco with a decel rate of 80g’s, when I started bleeding internally causing me to look much heavier than I actually am, unfortunately the actual story is quite simple and somewhat boring.

The incident happened on Monday September 29th which was the first day of Industrypool for the 2 week September session. It was also our first day on the track since September 2013. The track was open from 1 to 5pm conditions were dry (although it started raining shortly after the accident).

We were on the 5th and final session of the day tuning the dampers (our 10th lap). About 23 seconds into the lap, we entered the turn Hatzenbach exactly the same as we had during the previous 9 times. The car unexpectedly developed a vast amount of yaw acceleration rear to the left, I counter steered to the left, the rear of the car snapped back to the right and regained grip, immediately turning the car left head on into the Armco.

I wasn’t injured and we were recording data, and I thank god every day we were because immediately after the accident the only thing that perplexed me is “what happened”?

Upon examination of the data comparing the lap in question to the previous lap, up until the point the car lost grip, the speed, throttle, steering wheel angle, lateral acceleration etc., were pretty much identical.

I’ve put together a plot of Vehicle Speed, Throttle Position, Rear Wheel Speed, Steering Wheel Angle, Yaw Rate, and Yaw Rate Oversteer at the time of the incident. The Green Line is the previous lap, the Blue is the lap where the incident took place. As I stated, everything was line on line, then you can see a huge increase in yaw rate and yaw rate oversteer as well as the rear wheel speed at pretty much the same throttle position.



We sent the data files to Alex MacDonald our vehicle controls engineer and he stated that that only time he saw abrupt deviations in yaw rate in the oversteer coupled with a large decrease in lateral acceleration was when the car went from high coefficient of friction surfaces to very low coefficient friction surfaces. Not a dry surface to a wet surface, but a dry surface to ice or oil. So our theory is that another vehicle dropped a something slippery on the track and we hit it. Or, that’s my story and I’m sticking to it.

Some may also be wondering about data and video from out PDR system. The only thing I can say is the Nurburgring does not allow video recording during Industrypool time.

Being down 1 car was a major impediment to our goals for the remainder of the trip. We quickly moved to the blue automatic Z06, completing the Stage 1 and 2 aero package chassis tuning by the end of that week. One note is with the exception of heavy fog until about 10am, the weather the week of September 29th was outstanding.

Over the weekend of October 4th, 2014 our technicians converted the Blue automatic Z06 into a Z07. The changes included dampers, springs, complete brake assemblies, and an alignment including ride heights and cross weights and of course the correct rear caster.

Beginning October 6th, 2014, we completed a few days of tuning with the Z07. However, from sometime in the middle of the week of October 8th through November 15th the weather did a complete 180. During this time we never got an opportunity to run on a complete dry track. Between rain and fog, there were always sizeable wet sections prohibiting us from putting complete laps together. Also, in the 5 weeks between October 13th and November 15th, the track was open a total of 9 days, 4 of those were complete rain outs, the rest of them were with the track minimum wet. We cherry picked our opportunities on a partially dry track to complete the tuning on the Z07 chassis package.

Friends and collogues always forward me forum inquiries about a fast laps. As we have always said, the fast lap is a secondary priority. The mission primary objective is to complete the tuning of the car for European roads and European driving habits. Having said that, I live for a fast lap opportunity.

Please note, when tuning the car we run at about 95%. The reason for this is twofold, first is consistency, you must be consistent to properly tune the car. The second is because when tuning the dampers or steering I always have a passenger monitoring and recording data for the shocks or steering algorithms and making the desired changes. I refuse to begin my quest to 100% with a passenger. When tuning is complete I will then drive alone exploring the limits of the car. Sometimes we don’t get these opportunities and just go for it after a day of tuning. This was the case in 2011 with the ZR1.

Also, the opportunities for exclusive track time have been diminishing over the past few years.

In 2008 we were able to rent the track for 50 minutes 2 times. Both times we were able to obtain a 7:26, both times on the second lap.

In 2011, we were given 3 “last lap of the day” opportunities. The first lap in the ZR1 was just over 7:20 which was not bad as I had to keep in mind that there was still work left to do the next day. We then completed our tuning right before the second attempt and I was able “go for it”. The second attempt produced the 7:19. After the second lap, Jeff Mosher and I looked at the data from the 2 laps. We could see improvements in the 7:19 lap and agreed a 7:17 was completely doable but we had only one attempt left. We chose to run the Z06 with the Z07 cup package as this car was magnificent to drive on the Nurburgring and the fast lap time for the Z06 was officially still at 7:43 without cup tires and from a standing start. Please note: Our data shows the standing start increases the lap time by about 1.5 second. This is because the start line is well inside the brake point (when making a flying start) and very close to first turn. With a single attempt we recorded a 7:22 second lap.

In 2013 with the C7 Z51, we had several last lap of the day opportunities. Rain prohibited every one of those attempts. One of these laps, I started about 3 to 4 minutes behind the Z28. This was the lap the Z28 recorded the 7:37 finishing in the rain. When I encountered the rain the track was more saturated than what Adam Dean (the Camaro driver) had encountered. I aborted the attempt after an 80 MPH drift as the track transitioned from dry to wet. Also, our objective for the Z51 was to obtain a lower time than the 7:37.9 of the Carrera S, and I knew completing the lap for a time in the wet would put the car at risk as we still had work left to do.

Now for the C7 Z06. As indicated above, after the about middle of the week October 6th, we never got a complete dry track. Also our tuning objectives had not been complete. I did had a few opportunities on the very last day the Nurburgring was open for 2014 to run alone (in the car) on few the dry sections of the track for speed. We have data, we have segments, we have an idea what the car should be capable of. But we don’t post any time unless they are complete laps supported by video, so I have to just leave it at that. Sorry folks…

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Old 03-28-2015, 07:54 AM
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Default C7 Z06 vs C6 ZR1 at Milford

Original answer thread is here.

racerns asked:

The GM press release stated that the new Z06 (Z07) was a full second faster than the ZR1 on the 2.9 mile Milford course. There has been debate on this forum of the configuration of the ZR1 for that lap time comparison. Was it a PDE ZR1 equipped with the Sport Cup (1) ZPs or was the comparison done with a ZR1 equipped with the new Sport Cup 2 ZPs? Also, since the Sport Cup 2s were developed on the ZR1 can you give us some idea of the lap time improvements the ZR1 saw going from the Cup 1 to the Cup 2 tires? Thanks.
Tadged answered:

For the second week in a row, the question gets heavily into the chassis development work done by Jim Mero, so he provided most of the answer:

Jim Mero adds:
First of all, the Cup2 tires were not developed on the ZR1. The only time the ZR1 had a C7 Z06 tire on it was during an early comparison test between Michelin and Pirelli competing for the Z06 factory fitment. Each manufacturer provide sample tires showcasing advanced technology to be evaluated. The winner of the “shootout” would get both the standard and track tire business. This work was done in September 2011 before we had running Z06 prototypes.

In the Summer of 2013, we finally were able to put together a running prototype with a “roughed in” chassis set up. In September of 2013, we then paired up with the Michelin development team for the first round of Cup2 tire rides. And in typical Michelin fashion they came out of the box with a stellar tire. The team was elated to learn that on this very first day of track work, the Z06 on the new Cup 2 tires beat the track record recorded by the ZR1 on Cup1 tires by 0.4 seconds. Usually it takes months of development to surpass your previous best, but it was achieved this time virtually “out of the box”.

The reference to the ZR1 was relative to the fastest lap it ever recorded during thousands of laps run on the Milford Road Course over 2.5 years (late 2010 through early 2013). Naturally we were very excited that the chassis, aero, and new tires were proving to work so well.

As the car and tires progressed over the course of the development of the Z06 that delta to the ZR1 increased to about 1.8 to 2 seconds. As the team started running full tanks of fuel, the laps at the end of the tank in the Z06/Z07 were very close to the fastest laps in the ZR1 given similar ambient and track conditions.

As the development of the Z06/Z07 progressed the question of the Cup2 tires on the ZR1 never entered our minds. We were deep into Z06/Z07 development. Working the car every waking moment that weather and conditions would allow. We did not have the time or reason to dig out a ZR1, track prep it, use up a set Cup2 tries to acquire data that really would have been of minimal use since the C7 Z06 was performing so well. Generally speaking, when we reference any performance metric, we will always use the stock set up as it was shipped from the factory at the time.
Jim Mero adds:

Before we ever see the tires Michelin goes through an entire pre-screening process at their development site in Laurens, SC and they probably used a ZR1 for this. Their internal tests are conducted independent of our development process. The purpose of their pre-screening is to weed out tires that don’t perform as their analysis suggests. It is possible Pirelli went through a similar exercise as well. That could be where some of the media discussion came from.

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Old 03-28-2015, 07:54 AM
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Default Will Software updates ever be offered?

Original answer thread is here.

Hot Rod Todd asked

As a model progresses through it's life cycle, there are often updates that improve the performance of the engine or transmission in subsequent models. In some cases these updates could be passed down to older models with little or no adjustment to the program file. Many discussions I have had with other owners on this topic indicate that most believe that the manufacturer's use this as a way to lure them to the newer model, buy the newer model year and you get the better performance.

Example: The paddle shifting speed of the 2009 6 speed auto was significantly improved over the 2008 (and better yet in 2010). All of the improvement was gained through adjustments to the transmission programming tables.

I'm not talking about safety or warranty type downloads, which I know already happen on occasion.

My Question:

Do you think there will ever be a time when performance updates will be offered on non-current models, either at a charge to the owner or for free?
Tadge answered:

Good Question. I can tell you we never, ever, withhold performance intentionally knowing that with a simple calibration change we can improve it the following year and get people to buy a new car. We always put our best work out there and then keep trying to do better. Unfortunately, sometimes it may look like we could have done better from the start, but that is just not the case. The question asked about performance specifically, but most of our re-flash field bulletins relate to customer satisfaction in non-performance areas. For example, we changed a calibration to help the way the seat memory recall worked on manual transmission vehicles last year. I can't recall ever making an engine performance change though calibration.... Driveability, yes, but not performance. Quite often software, calibration and hardware changes are bundled together in model year changes and even though the hardware changes are subtle, they can affect the backwards compatibility of the calibration changes. This is certainly true of some of the shift speed changes we made as continuous improvement on C6's. We always attempt to specify how far back the cal is compatible. Sometimes it is just for the current model year, sometimes it can be used for several previous model years.

Your question is also forward-looking. It is true that vehicles' performance, features and character are more and more software-driven every day. I do think the future will hold more upgrade capability and customization than we do now.

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Old 04-13-2015, 04:59 PM
  #10  
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Default PDR Video Quality

Original answer thread is here.

ChrisN123 asked:
Why do all the PDR videos published to date have a distinct green cast and overall washed-out look? The camera hardware/firmware must allow for better calibration of color balance and white balance. How about a firmware update to fix the problem?
Tadge answered:

This is a perfect example of continuous improvement and backwards compatibility that I was asked about a couple weeks ago. GM engineering and our partner Cosworth have been working hard to improve the PDR and the user experience. One area of investigation has been the image quality. Coincidentally, a software change was just released for Bowling Green production at the end of March and we will be making it available to customers who already have their cars in the next few weeks. The software includes several changes including improvements in color balance and sharpness of the image on the video.

Here are some actual images comparing the original and new calibration:

Initial release for 2015 model year:


Current production software:


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Old 04-25-2015, 09:49 AM
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Default What Does an Extra $100M Get You?

Original answer thread is here.

Bwright asked

Bob Lutz said recently that for development of the C7 the team asked for $900mm but instead was only given $250mm. Given how good the C7 is I am curious, how might the car have been different if the team had been given say an extra $100mm? Just trying to get a better sense of how much $100mm buys on a program like the Corvette today.

Thanks in advance
Tadge answered:

Thanks for the question, Bwright: First of all, my recall of the budget requests for new Corvette programs differs a bit from Bob's recollection and I can't quote the actual figures because that is a trade secret. Suffice it to say, the auto industry is very capital intensive and operates on relatively thin margins. In a typical car program, we spend hundreds of millions of dollars years before producing the product intended to pay back that capital. The way GM works, and I suspect most auto companies do the same, is to evaluate each car program as a financial investment with potential risks and rewards. Corvette is no different. When we go to the leadership of GM with a proposal for a new Corvette, we have to understand the full cost structure including how much we have to pay for tools to make the parts, how much the development cost will be, how much it will cost to change over the assembly plant to produce the new vehicle, how many we expect to sell and how much we are going to make on each car (price minus variable cost per unit). We have strict financial goals that must be met to be granted program approval. These are Board of Director-level decisions on major programs.

This long-winded preamble is to point out that we are not "given the hundred million", we are loaned it and are obligated to pay it back with interest and profit. On a low volume program like Corvette, $100M is an enormous debt that is very tough to pay back without adding more price (not popular with customers and would reduce sales) or cutting cost on each unit (would lose performance and would reduce sales). So this is a multifaceted problem we have to solve: How can we do a new car, add technology and performance, make it more appealing so sales increase, but hold the line on cost so we don't have to raise price significantly. We have been quite successful at solving this conundrum on the seventh generation Corvette and so are enjoying excellent business results that gives GM leadership confidence that Corvette programs represent a good investment. I have to thank our customers at this point, because without them, we have nothing, no brand, no business, and no great product for we engineering geeks to work on.

So if I was asked how to improve the Corvette with an extra $100M in the budget, what would I do? Probably increase customization, make more models catering to individuals preferences. We could expand the bandwidth on the performance end by producing more hard-core cars and track-only models. On the luxury end, we could have more unique interior options - both aesthetic and functional. Of course all this would come at a price... We would have to pay back that hundred mil somehow.

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Old 05-14-2015, 09:03 AM
  #12  
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Default An optional cooling pack for C7 (track use or other)

Original answer thread is here.

SBC_and_a_stick asked:
Does GM have any plan to sell a cooling pack in the future for the C7 chassis? Is it even a possibility, and if so, what would it look like?

Background
The limitations of the radiator and related parts that help the car stabilize oil and water/coolant temperature are easily reached when the C7 Z06 is driven aggressively (such as on a track at an HPDE event). There are now many reports from owners overheating the cars in 80 degree weather or even in 70 degree weather. This limitation of the car as sold will be exacerbated in the coming summer months. Many media outlets have reported overheating. This includes every occurrence when Motor Trend tested the C7 Z06 and during daily driving the C7 Stingray by Edmunds. See here:
http://www.edmunds.com/chevrolet/cor...tain-road.html

The commonly displayed overheating message is "Engine Overheating, A/C has been turned off, please idle engine." Coolant temperatures in particular quickly approach 257 degrees which prompt the computer to issue a warning in the center display.

Other manufacturers offer such an optional package to effectively cool the car. See for example the new Shelby GT350 Track Pack is described as follows: "optional with the Track Pack, an engine oil cooler and a transmission cooler."

https://media.ford.com/content/fordm...0-mustang.html

Tadge answered:
I see the reference to both Stingray and Z06, so I will address both starting with the Stingray: We do all of our track validation with the front plate removed and I am not aware of a case of overheating when a Z51 car is properly prepared. The article referenced talks about cooling issues on the street when driven aggressively in hot temperatures with the front plate installed. I see in the picture of the Edmunds long term test, the car has a front plate in what we call the "show" position and so when driven very aggressively had insufficient cooling. As discussed in the owner's manual, this panel is "to be removed when driving aggressively or in hot weather". All cars shipped to states that require front plates also have a plate frame that mounts higher on the bumper and does not block as much of the cooling flow. Because states have varying height-to-ground requirements the plate holder sits high on the front bumper to accommodate those laws. While fully legal and beneficial for cooling performance, it doesn't look very good and many customers have asked for a more integrated solution, hence the optional "show" position centered on the grille. Although intended as a "show" position, for 99% of street usage the cooling performance is fine. Some may be quick to point out that other cars seem to be able to have low front plates and robust cooling (fourth and fifth generation Corvettes, for example), but those are "bottom breathers" with major compromises to down force performance. Although there are very few complaints from Z51 customers on cooling issues, we are looking at taking some of the learnings and hardware from the Z06 and making them available on the Stingray. For example, the front-mounted supplemental trans cooler developed for the Z06 automatic will be included in the Z51 package for automatic coupes starting in the 2016 model year.

We have discussed the Z06 cooling robustness in this space before and are very concerned about what some customers are experiencing. We have built over 8,000 Z06's so far with the vast majority of them having no cooling issues. We are working to gather data from customers (some of whom may have posted here) who have concerns and are in the process of sorting through that. We have found a few build issues, a few prep issues, and some vehicle mods that have hurt cooling performance. An example of a build issue would be an improper bleed of the intercooler circuit. Even a small air bubble can impact performance. As I indicated in in my last "Ask Tadge" answer, we design for 30 degrees centigrade and have for decades without customer dissatisfaction. We may have to move our target upwards since customers appear to want to run their cars very hard at elevated temperatures.

The question asks about what kind of cooling upgrade could be made available through GM performance parts. I can tell you we are looking at a variety of robustness improvements that could take many forms. It could be in calibration (and for followers of these threads, we haven't forgotten about the "rough track" chassis calibration talked about a few weeks back), cooling system or specification changes, or even super charger hardware tweaks. It will take us a while to work through what makes the most sense and to do the validation, but we will make every effort to make sure that the changes are backwards-compatible to vehicles already produced. In the meantime, we sincerely appreciate the customers we've contacted openness and willingness to work with us on continuous improvement.

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Old 05-29-2015, 04:47 PM
  #13  
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Default The design philosophy on the C6 was correct, but wrong on the C7

Original answer thread is here.

grcor asked:
There is a segment of Corvette loyalists that want a track originated car. The C5 and C6 Z06’s are perfect examples. Unfortunately the C7 Z06 doesn’t follow the same design philosophy as the previous Z06’s. It’s much heavier, overheats, provides an open air experience, and has rpm limiting cylinder deactivation. You did succeed in broaden the appeal by adding an automatic transmission option, but by trying to broaden the appeal beyond the track, it is no longer the purely focused track car of previous generations. Why did you call it a Z06 and I hope you understand what we really want in a Corvette Z06?
Tadge answered:
Whenever we design a new car, there are many things we have to take in to consideration, some of which are obvious to the public, but many are not. I understand exactly the sentiment behind this question because I was the principle engineer putting together the product plan and content for both the C5 and C6 Z06. I was working for Dave Hill as the assistant chief engineer and I took the lead in defining what could be done to create a more capable version of the standard Corvette. I was very proud that we introduced the C6 Z06 at 3132 lbs, by many measures the most mass efficient vehicle in the world. The only Corvette I have purchased for myself is a 2006 Z06.

On the C7, our original Z06 concept was much the same as the previous two generations except we did have very strong customer input that they would like an automatic and open air options. I assumed a naturally aspirated 7.0L with direct injection and variable valve timing would be the power train choice. The main reasons we ended up going to a charged solution had to do with regulatory changes and a strong desire to increase performance, not to stay the same or inch up only slightly. For performance, we knew the standard Stingray was going to be a pretty big upgrade over even the Grand Sport, so the Z06 had to be an even bigger step up.

On the regulatory side, on average, every business day, a new law governing the design of automobiles goes into effect somewhere in the world, and no space is more active than fuel economy and vehicle emissions. Porsche just announced an all turbo line up for the 911 in the future. Like it or not, regulators around the world are pushing manufacturers into lower displacements and charging to achieve higher output. With this reality, when we studied an LS7-like solution for the C7 Z06 we found only a very modest power boost would be possible while still meeting all the other new requirements. Cylinder de-activation played no role in constraining our choice. We only added it back in when we went to the supercharged solution where the rpm limiting was no longer an issue. You are right, charging brings mass, and cooling challenges, but it also brings a lot more horsepower.

I have heard comments that we shouldn't have added mass to go to open-air or improve our structure. However, the net mass penalty for open air is relatively small, as the added mass is attributed to many things. There are a bunch of regulations that either don't apply to convertibles or have delayed implementations, and meeting them adds mass. We knew chassis loads were going to go up with better aero and more capable tires, so we had to react those forces. If you read some of the media scrutiny of the C6 Z06, we were often criticized for not being as secure or confident at speed as our competitors, which had a lot to do with vehicle structure. We were relentlessly bashed for "floppy" seats on the C6. Each C7 seats weights about 10 pounds more than its C6 counterpart. My point is much of the mass increase has nothing to do with a change in philosophy, but rather improving the driving experience in many different areas (not just an open air top, or new seats).

Believe me, we are well aware of the very vocal group of customers that demand a more focused track vehicle. Although I hear claims that many people want that type of vehicle, it is not validated in the sales figures of cars like the Viper ACR or Porsche 911.

If you look at the Z06 (C6 or C7), hardly anybody orders the pure track car - no options but Z07 and maybe Competition seat. The vast majority (93% in 2015) are ordering their cars with uplevel option packages. This is not surprising, as every time we added features to the C5 and C6 Z06 (power seats, power column, heads up display, leather interior, magnetic ride control, to name a few), they quickly became incredibly popular.

Obviously, I am defending our choices for the C7. And our sales are very strong, ensuring we will have Corvettes for years to come. However, we take customer requests very seriously and usually find a way to incorporate them into our future plans. So don't lose faith. We are listening.

So why did we call it a Z06? Yes, it is a bit different formulation than the last few generations. It is however consistent in that it is the quickest car around the track we know how to make. That has been validated by numerous third parties. Last week, we were finally able to confirm the performance of the car on a continuous lap of the Nurburgring. We are putting together the press release and will have the lap time and video out shortly. I can tell you we were more than satisfied with the results.

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Old 06-10-2015, 10:05 AM
  #14  
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Default Eccentric Bolts vs Camber Plates

Original answer thread is here.

jvp asked:
Has your team considered replacing the Corvette LCA eccentric bolts with camber plates, and handling camber and caster with shims on the UCA? It might make alignments take a bit longer the first time, but they'd hold more solidly for those of us that like to track our cars.
Tadge answered:
At the Bowling Green assembly plant, a new Corvette comes off the line every 3 minutes. We custom align every car very precisely – it is super important on a car with such high performance tires and customer expectations. Cam bolts are infinitely adjustable within their range. Cams provide the most productive method of giving the best adjustment every time accounting for any body and cradle assembly dimensional variation.

The front upper control arm is very symmetric, so using the lower control arm is better for independent camber and caster adjustment. We adjust camber with the cross car part of the arm (handling bushing), and the caster adjustment with the more fore/aft part of the arm (ride bushing). Also, the spread between the bushings is bigger on the bottom which allows for finer adjustments.

The rear upper control arm is not symmetric. So there could be some benefit to use the upper versus the lower arm which is symmetric for camber vs. caster adjustment. However, the larger spread is still better on the lower control arm. Upper control arm washers are used to make big nominal shifts in camber. It allowed for minimizing the cam bolt size/travel required and permitted us to have different nominal camber settings between Stingray/Z51, and Z06. There have been some observers surprised that we have adjustments for rear caster. We use that to make sure we don’t have rear caster contributing to rear ride steer.

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Old 06-26-2015, 10:04 AM
  #15  
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Default C7 Z51 A8 Transmission Cooler Upgrade

Original answer thread is here.

AliZ51 asked:
Is it possible to install the C7 Z06 A8 secondary transmission cooler on a 2015 C7 Z51 A8? If yes, what would it take to get this done? If no, what can be done to bring extra cooling capacity to The Z51 A8 transmission?

Many 2015 C7 Z51 owners are dealing with transmission overheating issues on the track even in low ambient temperatures. The dealers are not able to help or address this issue. We know now that the 2016 Z51 will come with a secondary transmission cooler but what about us (2015 Z51 A8 owners). We do need a retrofit kit and instructions for the dealers for us who purchased the 2015 Z51 package in order to run on the track or spirited canyons drives.
Tadge answered:
One really good thing about the "Ask Tadge" section of the forum is that it focuses attention on issues where we can help customers. This question is a good example. The short answer is yes, the 2016 A8 cooling content can be retrofit on both the 2014 (A6) and '15 cars. You can use most of the production parts for 2016 with a few minor tweaks. Through our Performance Parts organization, we are putting together a kit with the needed material and instructions. It is not a super easy installation, but will be doable by the serious enthusiast. It should be available by the end of this year.

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Old 07-24-2015, 03:02 PM
  #16  
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Default DI Impact on Valves

Original answer thread is here.

vettman96 asked:

Is there any issue known with deposit buildup on the back side of the intake valves due to not having a port injection system?

Is GM aware of, and if so do they have any plans for correction with the intake valve coking issue present in the direct injection platforms as a result of the PCV system. Many members of the community are seeing an excessive amount of oil and carbon deposit buildup on the intake valves after only 5,000-10,000 miles and worse with even higher mileage engines on the C7. While I understand the purpose of the PCV system as it relates to emissions, with the introduction of direct injection there is no longer a cleaning process in place that would be naturally present such as from a port injection system.
Tadge answered:


Good technical question vetteman96. The short answer is: No, we have not seen any issue with deposit buildup on the back side of the intake valves due to not having a port injection system.

You correctly point out that the continuous flow of clean air and gas over the intake valve tends to keep it very clean. That has been a characteristic of small block V8's for decades. Of course, appreciation of that characteristic is limited to those who disassemble their engines. Most customers are unaware.

Given that all SIDI engines give up that benefit in favor of other important attributes, we did extensive testing to make sure there were no customer-observable penalties. We intently looked for unusual deposit formation during the entire Gen 5 Small Block development phase (4 years) as well as the 200,000 mile in-vehicle long term testing. We have not seen anything unusual and zero performance degradation. Granted, deposit formation on SIDI engine intake valves is greater than what is seen with PFI engines, but the Gen 5 engines are typical for SIDI engines, and in fact better than other SIDI engines we have benchmarked. So the bottom line is that we believe the carbon build up is only an internal cosmetic issue, not anything that will affect customers over the life of their cars.

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Old 08-10-2015, 02:25 PM
  #17  
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Default Changes in engine cooling.

Original answer thread is here.

grcor asked:
For many years GM has used radiators with an engine oil cooler inside left tank for trucks, SUVs, and in the Corvette 2005-2007 Z51s. This method of cooling engine oil works well and has the added benefit of warming the engine oil during warm up. It also keeps engine room congestion and the number of pluming connections to a minimum.

The 2006 – 2010 Z06s use a large air/oil cooler mounted in front of the radiator. This method of oil cooling works well at the track, but in normal street driving it keeps the oil too cold. On a 50 to 60 degree day, it is common to see oil temperatures in the 120 to 140 range (DIC). The DIC is reading oil temperature from the bottom of the external reservoir, the oil first travels to the oil pump, then thru to the oil filter then thru to the oil cooler before it enters the engine. So the temperature of the oil entering the engine is even colder than what the DIC says. What is the optimum oil temperature for a LS7?

The 2011-2013 Z06s, 2009-2013 ZR1s, and C7 Z51s/Z06s use a coolant/oil cooler assembly to cool/warm engine oil. This method needs to have a coolant line plumbed from the block to the cooler assembly and from the cooler assembly to the radiator. The cooler assembly and extra plumbing would seem to add to engine room congestion and increased potential of coolant leaks as time goes on.

The current Camaro Z28 uses a bigger coolant/oil cooler assembly than the Corvettes.

Can you please tell us the advantages and disadvantages of each oil cooling approach from an engineering point of view and why you changed the oil cooling approach so many times?
Tadge answered:
To answer this question I consulted with Richard Quinn, our powertrain cooling development engineer who has a long history on Corvette cooling development:

In the early stages of designing a performance engine, we make allowances to divert a portion of the lube system oil flow for cooling. Engineers evaluate different ways to extract the heat energy required and select the best one for the application based on a number of factors. As you’ve pointed out, we’ve taken different approaches over the years on Corvette and each one had specific benefits for the powertrain and chassis at the time.

I mention the chassis as an important factor because throughout modern Corvette history and especially the last three generations, the performance envelope of the car has seen a steady, continuous increase. As cornering capability has improved, we’ve modified our lubrication and cooling strategy to match.

The earliest oil cooler you mention - the radiator end-tank style in the C6 Z51, removed 3.5kW of heat from the oil and deposited it into the main engine coolant system. The downsides of this method are the relatively small capacity limit and the oil-side restriction penalty. Moving any fraction of the oil from the engine to the radiator takes away from the main goal of the lubrication system which is first and foremost to supply the bottom end (main bearings) with good oil pressure. But in the Z51 package, the tradeoff was favorable and the cooling adequate for the operating envelope of the LS2 engine.

With the introduction of the C6 Z06 we had a chassis and tire package that allowed us to put much more power to the ground, compounded by an LS7 engine that loved to spin. Those elements drove us to add a much higher oil cooling capacity (roughly 16Kw) than an end-tank cooler could provide, so an air-to-oil cooler was selected as a ‘big hammer’ solution for the dry-sump motors, chosen for its ability to cool better at higher vehicle speeds. We made a conscious decision to go that route, as there are several downsides to air-to-oil coolers. They add airflow restriction, which reduces the effectiveness of the main radiator and impacts AC performance. There is unwanted oil-side restriction which takes some pressure potential from the main bearings. And as you mention, on cold days the oil will always be somewhat over-cooled. (Overcooling oil isn’t the worst thing, but it costs some fuel efficiency as colder oil has higher viscosity and more friction loss.) But for a car as track-oriented as the C6 Z06, this was the right trade-off to make, using a balanced take-off valve to bleed just enough oil to the cooler to satisfy cooling needs.

In the spirit of continuous improvement, in the 2009 ZR1 we increased oil cooler capacity further. We also needed to maintain higher main bearing oil pressure to support the huge horsepower increase of the LS9. That drove us to integrate the oil cooler as a liquid-liquid heat exchanger mounted as part of the engine assembly- a triple benefit, with more kW of heat rejection (almost 20Kw), reduced oil-side restriction, and elimination of the front-end airflow blockage of the previous air/oil cooler. This option also reduced the plumbing complexity, with only one small coolant circuit leaving the engine block to return to the main radiator coolant circuit. The downside is that the main radiator has to reject the heat extracted by this cooler, but the tradeoff is overall a net positive. We’ve been very happy with the integrated liquid-liquid oil cooler ever since we adopted it, as it has been a win-win over all of the previous alternatives in terms of capacity, restriction, and the ability to better regulate normal operating temperatures.

The Z/28 Camaro presented a unique challenge, with higher mass and gear ratios selected to carry very high RPM on track. It required a capacity increase in the liquid-liquid cooler system, and the team added a supplemental air/oil coolant radiator dedicated to providing colder water to the engine oil cooler. This had a double benefit of reducing bulk coolant temp and oil temp, but with a tradeoff consequence of added complexity and added mass.

As the Corvette chassis improves and continues to drive more lateral loads through the lubrication system, we are challenged to keep up with the increasing demand of racetrack use. We’ve gone from 3.5kW of oil cooling in the C6 Z51 to 21kW in today’s C7 Z06. You can be confident we’ll continue along this path as Corvette performance improvements dictate it.

Last edited by jvp; 08-08-2016 at 09:22 AM.
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Old 08-19-2015, 05:03 PM
  #18  
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Default How do the Various PTM Modes Change Parameters When in Track Mode

Original answer thread is here.

descartesfool asked:
There are 5 modes which can be selected on any C7 equipped with MRC when it is put into Track mode. The owner's manual and a few other documents already released provide some very brief descriptions of the changes to the car's various systems, but it would be very informative to learn more about how the different systems are affected for each mode, and how all the various systems interact. A more detailed explanation of each PTM mode would be very informative for people who drive on track. As well it would be good to know when all the nannies are turned off, which ones are still operating if any. And finally which mode should be used by which type of driver, and is it possible to have a dash display showing which PTM mode the car is in?
Tadge answered:
Although we have talked publicly many times and published quite a bit of documentation about PTM (and other chassis controls), there continues to be additional questions. Assuming this section of the forum attracts a very tech-savvy audience, we are going to give a more technical description than our usual public statements. At the risk of helping our competitors, I have asked Alex Macdonald, our lead Corvette development engineer and expert in chassis controls to provide the definitive treatise on PTM. So, thanks for asking….

Performance Traction Management was first brought to the market on C6 with the 2010 ZR1 and was available on C6 Z06’s with MR from 2011-2013. It has evolved with each new model of Corvette since then but still retains the same functions and philosophy as when it was introduced. All of this discussion applies to any Corvette with PTM, not just the C7. For C7 any Z51 with MR dampers and all Z06’s are equipped with PTM.

The first important part of PTM is the traction control function. This is the core of PTM. Later I will describe the other adjustments it makes to the chassis but the fundamental change in each mode is the logic and calibration of the traction control.

It will help to understand how the standard TCS system works when not in PTM. See Fig 1 for an example of a C7 Z06 turning left at 25mph and approximately 0.8G lateral acceleration (a spirited left turn). The driver steps to 100% throttle (point #1) which causes the rear wheels to start spinning. Prior to spinning up the tires, the TCS system doesn’t know much about the road surface conditions. It could be wet, dry, gravel, coarse concrete, smooth asphalt, etc. To determine the surface condition the engine torque is allowed to increase until the wheels start slipping a certain amount (point #2). They would continue to slip at this torque level so torque is quickly reduced to stop the slipping (point #3). The initial engine torque that caused the wheels to slip along with how much torque needed to be removed to reduce the wheel spin are used by the TCS to calculate the type of surface the car is on. Once the surface grip is known the torque is added back in to maintain an amount of slip that’s appropriate for that surface (point #5).



The drawback to this method is that the wheels have to over-slip past the ideal target at the start. This disturbs the cornering of the vehicle and requires the driver to adjust the steering angle. Further, bringing the wheels back down from the initial over-slip with a torque reduction dramatically reduces acceleration in order to regain stability.

The use of the PTM switch tells the car that it is definitely on dry asphalt (or wet asphalt in in mode 1) and that the driver is prepared for some amount of wheel slip. Since the surface is known the PTM system can make a good approximation of the maximum possible engine torque that will not over-slip the tires based on how hard the car is cornering and how fast it’s going. This torque estimate is used as a starting point (since no new information about the surface is needed in PTM) and then depending on the amount of slip that results more fine adjustments can be made. As the driver unwinds the steering wheel the tires gain grip and torque will be fed back in due to the lower slip. See Fig2 for the same maneuver described above but using PTM mode 2 this time.



As you look at these two examples one thing to note is how much more gradually steering and lateral acceleration can be reduced on corner exit in PTM vs normal TCS (Red and Tan lines). The initial over-slip in normal TCS is what prompts the driver to make this abrupt steering adjustment.

Each of the Traction Control modes in PTM are differentiated in two ways. First, the target slip levels are lower in the lower modes as you would expect. Second, the estimate we make for the starting torque is lower. In DRY we err on the low side with our estimation and may have to increase torque to reach the target slip. In RACE we err on the high side and the driver may have to use more steering correction to manage the extra slip in the rear until the target slip can be recovered.

Along with the traction control, the other chassis subsystems are modified for the conditions expected in each mode. The following is a chart of the status of each subsystem for each PTM mode:



Mode uses:
WET: This mode is intended for any driver who is on a wet track. The track should be wet enough to be glossy, not just damp. A damp or drying track will require the driver to decide between WET and DRY modes to get the best performance. Standing water is not recommended as hydroplaning is possible and no TCS system can accurately control a tire that is hydroplaning.

The slip targets are very low, lower than in standard TCS. The MR is in tour mode to maximize mechanical grip since the lower cornering forces don’t require the extra control offered in Sport or Track. ESC is on and uses the normal calibration, not the competitive calibration.

DRY: This mode is for a novice driver on any track or an experienced driver learning a brand new track. I also use it to warm up the tires or run the mold release off of new tires, especially if it’s cold out.

Slip targets here are very similar to normal TCS but will feel very different due to the entry prediction. MR is in Sport to compliment the usage we expect in this mode. ESC is on but uses the competitive calibration.

SPORT 1: This mode is for any driver who is ready to run very competitive lap times while still having stability control on in the background. I use this mode whenever I have a passenger, possible distractions such as data collection, or as I am continuing to become more familiar with a new track.

Slip targets are higher here than in normal TCS. MR is in track mode and ESC is on using the competitive calibration.

SPORT 2: This mode uses the exact same traction control settings as SPORT 1 but turns off ESC completely. This mode is designed as a way to turn off ESC while maintaining a fairly stable TCS calibration. I use it very often. Basically any time where tenths of a second are not critical to my testing or when the tires are getting too hot or wearing out. After 10 to 15 consecutive laps it is likely that your fastest times will be achieved in SPORT 2 rather than RACE.

Slip targets here are the same as SPORT 1. MR is still in track mode and ESC is turned OFF.

RACE: This one is pretty self-explanatory, it’s as fast as we know how to make the car go. This mode is for a well prepared car on relatively new tires with an advanced driver that is completely familiar with the track. The track should be somewhat warm and the tires should be up to temperature.

Slip targets are 100% optimized for forward acceleration, any small variances in the track or tires can result in momentary overslip that will have to be managed by the driver.

A few notes about RACE mode: I approach this mode as a tool to go faster meaning that I think specifically about it when I go to WOT and I try to change or optimize my throttle application point and steering to help the computer do its job. It can do the job better than me but only if I give it good information. A specific example is how I unwind the steering wheel mid corner and as the corner opens up. When learning to drive on track it is good practice to automatically unwind the steering wheel as you apply throttle regardless of the vehicle response (a string tied from throttle toe to steering wheel is the analogy used by some instructors). The problem in RACE PTM is that by doing that you are telling the car you are ready to go straight. It will add power and drive you to a wider line. The best results are found by holding the wheel as steady as you can and pointing the car to corner exit only when it’s time. Obviously you have to be ready to correct for overslip but as you gain trust you will find this is required less often than it feels at first. It is very useful to practice using PTM in the lower modes where you can focus on letting the car go where you point it and not correcting your steering too early.

We find that the calibration settings that achieve the fastest lap times often result in expert drivers feeling like they are being held back slightly on corner exit. Most of the time that extra little bit of slip that an expert driver wants is over the traction peak of the tire and may feel good but is wasting forward acceleration. The restrictive feeling is not there as a safety net, rather, it’s as close as we can operate to the peak capability of the tire in a robust way.

Other notes: The eLSD “PTM mode” is only a slight alteration of its normal track mode. This alteration is required since it is likely to see engine torque values that would not occur without PTM. However, the philosophy of what it’s trying to do and how it’s controlling vehicle dynamics does not change between PTM and TCS/ESC OFF mode.

As for the nannies, that term is a big gray area. I would personally call TCS, PTM, ESC and active rev match nannies but would not call the eLSD or MR dampers nannies. ABS is very gray. ABS, TCS, PTM, ESC and active rev match are trying to do a better job of something you normally do as a driver, steering, throttle, brake or shifting. However, no driver ever controls a differential directly or a shock absorber directly. They are part of the base chassis tuning and can be thought of as a calibration component like a spring or anti roll bar.
ABS is more of a gray area but it is not allowed to be shut off because the capability of the vehicle is so limited without it. You may need 200 bar of brake pressure to get max decel from a wheel that’s on the outside of a corner but the inside wheel would be totally locked at 50 bar. Unless you want a lot of flat spotted tires you need ABS in that situation. Also, somewhat like eLSD and MR, individual wheel brake pressure is something even the best driver can’t physically control without the electronics.

That’s a long way of saying you can shut off TCS, PTM, ESC and active rev match but you can’t shut off MR, eLSD or ABS.

Last edited by jvp; 08-08-2016 at 09:23 AM.
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Old 09-16-2015, 10:36 AM
  #19  
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Default All Season Performance Tires

Original answer thread is here.

b4i4getit asked:
Would it be possible to make an all season performance tire available for the Corvette ? Certainly GM has enough pull with the tire manufacturers to get one of them to develop a runflat that would be usable all year and would have some level of performance. This would be beneficial for those that like to use their cars all year and have no track aspirations and would also eliminate the tire cracking issue that many have experienced.
Tadge answered:
As we, our competitors, and tire manufacturers push the edge of the envelope on performance tires, the focus on dry traction tends to compromise traction in wet, muddy, cold and snowy conditions. Although we validate the corrosion, durability and performance of the Corvette in all weather, most customers are extremely reluctant to expose their cars to bad conditions. I've seen the majority of cars at a show disappear with just a prediction for rain. Some customers even rented local garages to keep their babies dry through a storm! Although one would assume we have some influence over the aftermarket offerings of our tire suppliers, we wouldn't be very good business partners if we forced companies into money-losing businesses. It is very expensive to put a new tire into production. The tooling costs are quite high (with unique tools for front and rear on Corvette due to our staggered sizes) and then there are design, development, and distribution costs. Since Corvette has tire sizes not shared by many other vehicles, our customers tend to be the sole source of business to pay back the cost of developing the tire. Our history is not good here. Years ago we encouraged Goodyear to make winter tires available in C5 sizes. Goodyear did just that and the only customers who bought the tires were our own GM development engineers who wanted to keep their Corvettes on the road through the Fall and Winter. Needless to say, with just a handful of sales, that was not a good business for them.

Although this sounds pessimistic, all is not lost. We are still very motivated to enable customers to use their cars for more of the year and have had quite a bit of feedback along the lines of this question. As the original equipment tires become more performance-focused, the argument for a good all-weather tire alternative becomes stronger. Michelin has been an excellent partner and already offers All-Season tires in Stingray sizes (Pilot Sport All-Season ZP's for the standard suspension and non-ZP's for Z51). We have further agreed with Michelin leadership for the additional offering of All-Season ZPs in C6 Grand Sport and Z06 sizes, in addition to the C7 Z51 sizes. The development of those tires is underway and the current plan is to have them available next year (third quarter at the latest). That leaves the C6 ZR1 and C7 Z06 uncommitted at this point. Michelin is currently studying adding those to the A/S portfolio as well.

Interested customers can check http://Michelinman.com for all the latest Michelin Corvette tire offerings.

Last edited by jvp; 08-08-2016 at 09:23 AM.
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Old 10-02-2015, 03:29 PM
  #20  
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Default How Does No-Lift-Shift Work

Original answer thread is here.

BJ67 asked:
Exactly how does NLS work and exactly what mode do you have to be in? and what other settings are required. Also does rev match have to be on or off or does the system work the same regardless of rev match. Non z51 base car. I know how to power shift but the technical details are important.

Tadge answered:
No Lift Shift (NLS) works in all driver modes and with rev match on or off. In other words, all the time. Many manufacturers seek to reduce the stress in their drivelines by sensing the conditions for a power shift and close the throttle regardless of what the driver is doing with the throttle pedal. The problem with closing the throttle is that when the next gear is selected and the clutch is re-engaged, the intake manifold has very low pressure. The throttle then has to re-open to fill it and feed the cylinders. Although this all happens very quickly, there is a delay for the engine to back up to full torque (and these effects are magnified in charged engines where intake manifold pressures are higher). Although I can't share the calibration details, the NLS algorithm looks for the conditions where the driver is requesting maximum performance and, within certain bounds, keeps the throttle fully open during the shift to keep the manifold pressure relatively high. In this way the engine is ready to provide full torque upon completion of the shift. The performance difference is easily measured in our straight line acceleration testing. And of course the Corvette is designed for and fully validated for this usage.

Last edited by jvp; 08-08-2016 at 09:24 AM.
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