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Patman asked: I'm curious if the algorithm is exactly the same for the oil life monitor on the dry sump equipped cars as it is for the wet sump equipped cars? With the extra 3 quarts of oil in the dry sump (30% more oil), in theory the oil should last longer between changes and therefore I wonder if the OLM allows for that extra mileage possibility? Also, how does the OLM take into account both the time factor and the mileage factor?
Tadge answered: Great question, Patman. This is one I bet a lot of people are curious about. Obviously, maintaining the quantity and quality of the oil in your engine is paramount for long term durability and performance. There are many things that work to deteriorate the quality of your oil and we make the oil life monitor (OLM) as accurate as we can to predict oil life in consideration of all of those variables. The simplest variable is the length of time the oil is in the engine. As you surmise in your question, this is an important variable. Oil ages sitting inside your engine differently than in a sealed container. It is exposed to more oxygen, humidity, various sealants and a variety of metals in your engine. Also, time causes things you might not expect to have an influence such as oxidation of your oil filter. To account for this variable there is an OLM clock that begins a year-long count down every time it is reset. So that is the best you can do…. Change your oil and filter once a year.
You also surmise that mileage should be a factor. We could use mileage, but it is more accurate to actually count combustion events. Every time the fuel and oxygen ignite in the cylinder a tiny quantity of contaminants slip past the piston rings and gets into your oil. Over time, these contaminants build up and hurt the oil’s lubrication capability. You can see this effect as the oil darkens over time.
OK, but all combustion events are not created equal, right? There is a big difference between cruising down the highway under light load and tearing it up on the track. On the highway, the coolant and oil stay relatively cool and there is little stress on the engine. On the track, when oil temps are high, oil molecules actually fracture and that hurts lubrication performance. We handle that buy adding a multiplier that compounds the number of combustion events that occur at higher temperatures. The hotter the oil, the more heavily we weight those events and the shorter the life prediction. On the other hand, running your engine at low temperatures stresses the oil as well. So we also have a multiplier that over-weights combustion events when it is cold. People who drive in cold climates and take relatively short trips are going to find they have shorter oil life. The display in the cluster is regularly updated to the lesser of the time-based or use-based metrics.
Lastly, to get to the first part of your question: No, the dry-sump cars do not use the same algorithm as the wet-sump. As you theorize, having more oil dilutes contamination and distributes thermal stress across a greater quantity of oil. Those are both true and, even though you get some life extension, it is not in direct proportion to the total quantity of oil in the system. Why not? Well the time-based degradation is very insensitive to oil quantity. And don’t forget the oil in dry-sump cars get more exposure to air and system metals (and other materials) because of the tank and plumbing. The extra oil quantity helps roughly in proportion to volume for contamination, but not quite in proportion when it comes to thermal stress. Since dry-sump cars are more likely to see track duty or hard street driving we tend to be a little conservative to make sure oil is changed before it falls below a performance level needed to assure perfect operation of your engine. Bottom line is that, depending how you use your car, the dry sump will have at least the life of wet sump, and probably somewhat more.
Poor-sha asked: In the past you have answered questions about the center rubber deflector that is only present on C7 base and Z06 cars without the stage 2 or 3 aero. However, what is the aerodynamic effect of the smaller side deflectors that hang under the splitter in front of the front tires (seen below)? They have been described on the Camaro as there to increase front downforce but it appears as though on the C7 ZR1 these are only present on non-ZTK cars. Do the deflectors increase or decrease downforce and can they be used to tune front aero grip? Also, is there a likely aero benefit to using helicopter tape or an equivalent to cover over gaps in the front underwing like the recessed bolts and the radiator supports? As always, thanks!
Tadge answered: The ZR1 has, by far, the most downforce of any Corvette we have ever built. Getting that much downforce on a street car is very challenging and it is quite rare in the auto industry. Some auto makers talk about the downforce of their aerodynamics aids as independent features. They say things like “this spoiler generates XXX lbs of down force”. The entire vehicle may actually generate lift, but the impression is left that the car has true down force. When we talk about the ZR1 ZTK package generating 950 lbs of down force, we are talking about the whole car as a system. The most visible part, the big wing, is only part of the story. Sometimes that subtlety gets lost in some of the descriptions of the car.
When we start designing an aerodynamic package for Corvettes, we start with the front of the car. Down force on the nose is is the toughest to get. We developed a structural under wing similar to what the C7.R uses and tuned it to get maximum performance. Then we tuned the rear wing size, height and shape to precisely balance the car. We shoot for a pitch moment (think of the relative power of the front and rear aero aids) that keep the car stable and easy to drive all the way up to top speed. Too much down force on the rear relative to the front makes the car understeer and vice versa makes it oversteer at speed. This is obviously a gross simplification since we are simultaneously working driveline and brake cooling as the surfaces develop. We generally start with the max down force configuration (ZTK in this case) because it is easier to de-power aero aids than find more performance once they are designed. The image below on the left shows the underwing pressure distribution on the ZTK package. The blue color indicates low pressure or downforce. On the right you see a very different looking pressure distribution created by the tire deflectors, or air dams. Despite being relatively small, those features de-power the underwing by disturbing the flow pretty dramatically. High pressure in front of the dams causes the effect, but because they keep air from impinging on the front face of the tire, the net effect is actually a drag reduction. We can then pair the de-powered underwing with a smaller wing at the back of the car to yield a package that trades some downforce for drag reduction. This is why the standard ZR1 has the highest top speed.
As to the question on taping gaps…. You are right that creating smoother transitions will help drag and downforce performance. The effect is very small, but because it is more likely to improve front performance, it is in the less conservative direction for pitch moment – it will tend to make the car oversteer. We optimize the car for the real construction coming from the factory, so we don’t recommend additional sealing. Also, since we don’t test with those gaps completely sealed you may cause other problems. For example, hot soak issues where we count on convection drawing cool air from below the car after it stops moving or splash drainage when you drive on wet roads.
black_c7 asked:
In previous thread tadge answered Fyreant that all c7 manual cars have the same axles, but I found that base c7 have a different axles parts number (20977316 left side + 20977317 right side ), for c7zo6 and c7zr1 (23301162 left side +23301163 right side), pricing is different from both part numbers.
My question is why there is different part numbers and different pricing if they are the same axles?
Also: is the transmission in c7zo6 is the same as the c7zr1 for manual trans?
Tadge answered:
In reviewing my answer to Fyreant on ZR1 hardware upgrades, what I said was: “The half shafts and prop shaft assembly are carry over from Z06”. That was and still is true. There are a number of part numbers in our service catalog because left and right half shafts are different in diameter and there have been continuous improvements over time. We traditionally use half shafts of different stiffness’s on either side of the car to help with power hop. Power hop occurs when spinning the rear tires on surfaces with friction characteristics that create a stick/slip condition. The stick/slip phenomena alternately winds and unwinds the driveline like a big spring preventing smooth acceleration and creating quite a disturbance in the car. Having a very stiff half shaft on one side will break that tire loose sooner than the one on the other side, creating an asynchrony that helps dampen the resonance of the system. The part numbers you quote for the base C7 are in fact parts that were released for the 2014 model year Stingray. They have a unique interface and so can not be replaced with the newer part numbers. All manual transmission Corvette since the 2015 model year use the 62/63 part numbers. You do see some minor price changes between the older and newer part as our suppliers change the price to us, but the big difference is left to right. As I describe above, the stiffer half shaft is designed with a larger diameter. There is more material and a more complicated construction, that is why the right side parts cost more than the left.
The answer to your final question is, yes, the manual transmission assembly number is the same for Z06 and ZR1, we build both cars with the same trans.
The HACK asked: With DEXOS 2 oils widely available on the shelves, are there any harm in using non-Mobil 1 5W-30 weight, DEXOS 2 approved engine oil for street use? For mixed track and street use, can 5W-40 DEXOS 2 motor oil be used in place of Mobil 1 0W-40 ESP for any C7 Corvette, especially in warmer climates where operating temperature never dips below 40 degrees for a non ZR1?
Actually, the real question is, can non-Mobil 1 or AC Delco motor oil that meets the DEXOS 1 or 2 standard of the proper weight (and what IS the proper weight?) be used in place without voiding warranty on a C7 Corvette?
Tadge answered: All Corvette engines have been engineered using GM Dexos approved engine oil, so any use of non-approved oils could, over time, result in sub-optimal engine performance. Many engine functions, including cam phasing and AFM (cylinder de-activation), rely on the correct Dexos approved engine oil to function, while providing the driver with the optimum drivability and ownership experience. Of course, your owner's manual has the best information relative to your specific car. Since it is impractical for us to test all customer-available oils, we can't make any blanket statements on which are ok and which are not. Oils we do have confidence in are listed here: www.gmdexos.com So the answer to your questions on the risk of harm to your engine is not a simple yes or no. Honestly, you probably won't have an issue using alternative dexos-spec oils, it is just impossible for us to make a definitive statement. There is more to worry about than warranty coverage, inferior lubrication could harm your engine over an extended period resulting in problems long after the warranty expires. With something as important as your engine it is better to be safe than sorry.
You ask about Mobil 1 specifically. We have had a long and productive relationship with Mobil lubricants. Corvette Racing uses Mobil 1 products in their quest to remain America’s premier production-based sports car team. Because of the great racing heritage and success of the Corvette and small-block V8, GM recommends Mobil 1 engine oils that show the Dexos approved logo for its dry sump-equipped engines. For the LT1 and LT4 engines only, if a 0W-40 Dexos 2 engine oil like Mobil 1 ESP is not available, a SAE 5W-30 Dexos1 Gen 2 engine oil may be used for street use above 45F. For aggressive usage, such as the race track, the oil weight and capacity is more critical, so you will want to be sure to use the recommended oil weight and capacity as specified. The recommendation varies depending on your Corvette trim. However, 5W40 could still be substituted for 0W40 as long as it is Dexos approved and above 45F degrees.
ZMMMMM asked: I have a perception that Corvettes (and all cars) nearly always fishtail to the RIGHT. I’m wondering if Corvettes are engineered to do this (different shaft sizes, (e)LSDs, alignments, etcetera), OR, is there some physics explanation (road crowning, differences in weight, etcetera), to explain my perception.
Perhaps, it is a safety feature designed to prevent cars from fishtailing into on-coming traffic. Thx!
Tadge answered: Interesting question, ZMMMMM.
I can tell that by design, we try to make the car handle the same whether turning left or right. I am assuming by "fishtailing" you are referring to oversteer, or the cars tendency to rotate, or yaw, more that the driver's request based on steering inputs. We design the car as symmetrically as possible: The suspension geometry is mirrored left to right and of course the tires are as perfectly symmetrical as Michelin can make them. There are limits however. Some manufacturers have gone to such extremes as placing the driver at the center line of the car, but that makes entry/egress a real chore. With the driver positioned on the left side, we are forced to place instrumentation steering, brake and throttle controls on the left as well. When added to the driver's mass, it makes for a pretty significant left-bias in the weight distribution. We can do things about that too, such as placing the battery and other heavy components on the right side. The fourth gen Corvette even went so far as to move the engine and trans to the right of center, but that resulted in a very small passenger footwell. There are other asymmetries too such as the gyroscopic forces generated by a spinning engine, but I believe they are too small to explain a general tendency to oversteer to the right (i.e. when turning left).
I think you guessed the major factor in your question: Road crown. Although barely noticeable on many roads, virtually all have some degree of crown. Road engineers put 1-2 degrees of crown in roads to shed water efficiently and avoid hydroplaning. That may not sound like much or even be perceivable from the driver's set, but 2 degrees gives a side load of over 120lbs on a 3500lb car. That means even when driving straight, dynamically the car is behaving like it is cornering about 0.035G's. The probably seems trivial, but when you are approaching the vehicle's limits, say 1.0G, that can make the difference between gripping and slipping. Compounding the asymmetry, when you are rounding a right-hand turn, the road crown acts like a banked turn and you have the same side load as a starting advantage making the car feel more secure.
I have to be honest, we do not have data validating the premise of your question, and I certainly can not speak for other manufacturers, but this is the most plausible explanation I can think of. Thanks for making me think about it.
ArmchairArchitect asked: Makes it very difficult when searching for parts. There are thousands of other possible combinations of 3 characters (or more) to use...why reuse the same engine names?
Tadge answered: For many decades, General Motors has used 3 character alphanumerics to denote regular production options (RPO's). Although it might seem like there are a virtually infinite number of combinations, they are not simply random letters and numbers. Starting in 1963, RPO's were organized to convey information about the type of option they represented. Not just on Corvette, but across the company, a convention was established that made the RPO's more logical. I can't tell you why, but engines fell under an "L" categorization, so for 1963, L75, L76 and L84 engines were offered. Transmissions fell under an "M" category and for '63 we offered the M20 and M35. Similarly, braking systems started with "J" and suspensions with "F".
Over decades, certain RPO's became brands of their own having special meaning to dealers and owners (Think L88 in '67 or the LT5 in the C4 ZR-1). There are times we will re-use an RPO when we feel like the brand equity conveys the mission of the modern hardware. It give people a reference of what they are getting when the check the option box. Todays ZR1, also featuring an LT5 is a good example. Sometimes it is not a specific RPO but groups of engines sharing a common origin that guide our choices. The LT and LS designations have been used on a quite a number of small block V8's and so are logical choices.
I appreciate that it might make it somewhat easier to track content if every engine had its own designation versus having to know engine RPO plus model year, but customers tell us they have more than just a passing interest in the engine in their cars. We see a lot of people investing in additional badging for their vehicles trumpeting their engine RPO. It is that passion we are trying to respect with our choice of engine option codes.
jvp asked: I got to spend a lot of time at the Carlisle show back in August, crawling through the various engineering displays that the team brought down from MI. Thank you for that, as always. I heard you say this a few times during interviews, and even on the fairgrounds, "It turned out even better than we expected." Was there an "Ah HA!" moment? A point in time, or a development cycle that happened, where you and the team just knew you'd got it? Can you share that with us, in allowable details?
Tadge answered: Over the course of a long vehicle development you face many challenges and have many small victories. Four things stand out as "Ah Ha" moments.
The first one is when we got engine, trans and exhaust tuning close to final calibrations. In our collective minds, the combination of small block torque, horsepower and sound quality mated to a world-class DCT was going to be magical. It is. And feeling it and hearing it for the first definitely qualifies as "Ah Ha".
A second time was when we got the latest generation of our magnetorheological dampers working well on the new, super-stiff architecture. Placing the occupants center of gravity right on top of the car's plus the superior responsiveness of the new dampers gave us ride quality unheard of in sports cars, and very close to the best cars in the world in any segment. Early reviewers are confirming this seemingly implausible observation in their 3rd party assessments.
Third, late in the program, a number of us had the privilege of spending half a day on an autocross course comparing the seventh and eighth generation cars. We had a variety of driving skill levels represented in the group, and a lot of familiarity with the current car. Although the current car has gotten excellent marks for handling and driving dynamics, everyone came away with the eye opening contrast between the cars. The new car was so easy to drive right up to the limit that it made us all feel like heroes behind the wheel. I know some of the earliest reviews are talking about too much understeer at the limit, but that is not how we tuned the car. We are confident drivers of all skill levels are going to love the way the new Corvette Stingray handles.
Maybe the biggest revelation of all was the day we could drive the new Stingray for the first time without camouflage on the interior or exterior. It was like seeing in color for the first time. The whole world opened up with the panoramic view through the windshield and unfettered access to all the vehicle's controls. That was a joyous day for everyone on the team.
Can AFM be turned off by putting the car in manual mode? How long before it goes back to auto mode?
Assuming I purchase a Z51 with magnetic ride, can I disable AFM by putting it in PTM?
Tadge answered:
We know some customers are not fans of AFM (Active Fuel Management, otherwise known as cylinder de-activation). They worry it will sound bad, or feel bad as it transitions in and out of V4 mode, or just don't like that the engine doesn't always run on all cylinders. Manufacturers around the world are being put under tremendous pressure to reduce fuel consumption and greenhouse gases. As a result, you see a massive move to electrification, hybridization and small displacement charged engines. General Motors is fully embracing the initiative and has a stated goal to get to a zero emissions future.
So how does Corvette fit into this picture? Even before global greenhouse gas concerns became mainstream, Corvette prided itself on efficient operation. After all, low mass, low drag and efficient engines make for a better sports car. There are a lot of ways to get fuel efficiency and some of them negatively impact the driving experience. Our manual transmission skip-shift we had for years was not a customer favorite, but it helped economy and kept us away from gas-guzzler taxes. The bottom line is that we have to make choices that balance the owner's experience (including operating cost) and our impact on the planet.
Our AFM system is very effective on the small block V8. It lets us close the valves on the de-activated cylinders so the cylinders act as air springs. When the engine rotates we get energy back as the compressed air in the cylinder expands. Other manufacturers just stop fueling the de-activated cylinders and so don't get much fuel savings. The reason 4-cylinder operation is more efficient is that the active cylinders are worked harder with a greater throttle opening. That's like taking a restrictor out of the system saving pumping losses. On Corvette, AFM saves more fuel than start/stop, a feature becoming very prevalent in the marketplace. For many cars, start/stop is a great choice because it is almost transparent to the occupants. Not so on a Corvette. Our engine has a lot of character, so when it stops running it is very noticeable. We have received a lot of very strong input from customers that they would not like it.
One of the innovations on the 2020 Stingray is the integration of AFM with a DCT. We a quite proud of how seamless we've been able to make it. We believe we are getting the efficiency benefit with virtually no compromise to the driving experience. Numerous drive impression articles have been written and I do not remember reading any negative comments about it. Bottom line is that we must balance conflicting demands and make smart choices so we can continue to offer the driving pleasure of a naturally aspirated V8 engine.
So now to the heart of your question. Yes, when you are in manual mode the engine stays in V8. That is true either by hitting the "M" button or by entering "temporary tap" by pulling one of the paddles. Temporary tap will revert to "Drive" after about 5 seconds if you don't request an additional shift in that time. AFM is also de-activated in "Track" mode. Since PTM is only available in Track mode, the answer is yes to that one too. If you are in PTM, it will be V8 only. New for 2020 is the "Z" mode which will come from the factory set up as an extra sporty mode including shift schedules pulled from the "Track" mode, so that will be V8 only. Of course, you can customize "Z" mode any way you want, so if you elect another shift pattern, AFM will return.
jvp asked: During your recent interview with Jay Leno on his Garage show, you mentioned that the new car will be in a reduced torque output mode during the car's initial break-in period. Can you elaborate on the purpose for that, and explain to folks what happens at 500 miles? Does the engine's full output happen automatically due to programming or is it something that will require a maintenance visit?
Tadge answered: Thanks for the question JVP. This is a good opportunity to clear a few things up. For as long as I can remember we have recommended a 500 mile break in period for new cars. Not just Corvette, all cars. It has been emphasized in the owner’s materials with further definition around brakes and driveline.
Why is this important? Any machinery that has moving parts, whether they have point contact, a rotational interface or slide against each other will “bed-in” over time. What that means is, no matter the manufacturing process, two interfacing parts will find their own equilibrium. You can think of it as mutually refining each other’s surface texture until they reach a steady state. This steady state condition generally minimizes noise, vibration and wear. Although manufacturing has improved to a point where break in effects are minimized, they are still at play despite claims to the contrary. And the truth is, there may be additional minor benefits to a longer break in period. If it was my car, I would try to be patient for 1,000 miles.
Starting with the 7th generation Corvette we established a variable red line on the tach to give drivers a visual indication on when it would be advisable to take it easy on the car. We used it for the first 500 miles of driving and when the engine was coming up to operating temperature after break in was complete. Our reconfigurable display enabled us to to that. We didn’t actually limit torque, horse power or RPM, it was just a visual indication. Despite the tach and owner’s instructions, some customers use the full capability of the car immediately. We have too many videos of people doing burn-outs off the dealer lot or showing up to a track (both road course and drag strip) with near zero miles. Taking any green and cold engine to max torque and speed can cause undesirable wear patterns that could affect engine operation over the long term. Running full torque through the trans under the same conditions can score gears, especially those in the differential after the engine torque has been multiplied. We have had examples of customers not observing the break in guidelines and then returning the car to the dealer with complaints of gear noise or differential whine.
For the 8th generation Corvette, we have taken it a step farther. With more weight on the rear, the car has more traction and we take advantage of that with more aggressive gearing. That translates into more torque multiplication and more loads in the driveline. We decided for the first 500 miles to limit maximum torque in first and second gears. The torque reduction is roughly 25 to 30% depending on which transaxle (standard or Z51) and which gear. That may sound like a big reduction, but in reality the car is still really fast. In fact, you could easily spin the tires on some surfaces. Engine speed is not limited at all – it will wind out to redline. So the torque reduction limits the worse of potential break in wear, but is not a panacea. We will still be asking customers to stay well off max torque and speed for the first 500 miles. We know it is hard to stay patient when such performance is available, but it will pay off in the long run.
Batman 357 asked: Will the C8 with the Z51 option run a 20 minute session on a track day without overheating. Can you address cooling issues with the mid engine car in general. I would think you would need to put the water pump and AC compressor on steroids to move coolant around to all the radiators.
Tadge answered: Thanks Batman 357. Sorry I'm so slow to answer this one. I missed it in my email until last week. This is a question I really want to answer!
The C8 with Z51 option was designed to be capable of running back-to-back tank-of-fuel sessions (substantially longer than 20 minutes) without overheating any vital fluids. Our Z51 mission is to allow an expert driver to perform unlimited max-effort hot laps at a typical road-course racetrack at ambient temperatures up to 38C (100F)... All while keeping the AC on. Drivers who push the car even a little bit less will find the car capable above 100 degrees with the A/C on.
Our development testing has proven on a number of different tracks, that the Z51 cooling system is capable of maintaining stable temperatures with A/C On at 100F. Our drivers have noted that the most comfortable place to be at the racetrack on a 100F day is behind the wheel, turning continuous hot laps.
The Z51 cooling package can be pushed beyond 100F if the AC is switched off, but in that case we recommend use of a cool-suit, as the human becomes the weak link in the capability chain.
With the Mid-engine car, track cooling was given a strong priority with a distributed system of four cooling fans and two parallel-flow radiators up front plus a third radiator in the rear quarter inlet of the Z51. The water pump was designed to be a high pressure/high flow system and the A/C system is very robust with a dual series-condensing package. The plumbing to and from the heat exchangers are large diameter to enable very high rates of flow. The Engine and Transaxle each have dedicated liquid-to-liquid oil coolers sized to meet the needs of high-ambient track day use.
GRX2009 asked: One of the greatest things about Corvette is the continuous and generational improvement process. There's a lot of product integrity and listening to the proverbial "voice of the customer". MY by MY, Corvettes reflect lessons learned and new content. Can you detail how those efforts are put into practice? Specifically, how does Corvette collect suggestions from inside the team and from customers that are off the initial product roadmap, and then run them through a vetting process for production? Who's the keeper of the "suggestion box"? For example, if a bunch of customers wanted the front and rear cameras to perform security monitoring while parked, or a transparent or photochromic panel in the convertible hardtop, how would these suggestions flow through the organization and get considered? How fast can you do most elective changes?
Tadge answered: First of all, thank you for the recognition that "voice of the customer" is readily apparent in Corvette execution and continuous improvement. In most large companies, customer input is gathered via surveys or clinics where customers are invited in and asked questions. Most of the work is done by third parties and aggregated into formal reports for digestion by the company insiders. Sometimes the insiders participate in the clinic remotely or by closed circuit video. We don't do much of this kind of work on Corvette. We get our information mostly face to face.
We have the luxury of our customers gathering in large numbers at their own expense at car shows, Corvette-specific events and races. All we have to do is show up and talk to people. Of the hundreds of these type of events each year, we actively support more than 30 of the largest. We typically talk about the most recent product news, but are also there to listen and observe. When we hear a number of people asking for the same kinds of things, we really take notice and try to figure out whether there is a technical solution at a reasonable cost. In some ways, that is the essence of our jobs. Dozens of people with various responsibilities participate in these events. One of the weakness of typical survey and clinics is that sometimes, customers tell you what they think you want to hear. We are very careful to observe how people are actually using their cars, how they are customizing them and how they are integrating the car into their lives. The truth lives there. After most events we talk a lot together about what we saw and heard. No matter what our team member's specific responsibility is, everyone gets to talk about what they think customers want. None of us is shy about suggesting things that relate to other team member's responsibility.
Many of us on the team are Corvette owners as well and we all have strong opinions on what a dream car should be.
We also gather input on-line. Although there is a lot of noise and clatter on the various forums, we do pay attention to what people are saying and occasionally spot a nugget or trend. There is no one person responsible for canvasing the entire internet, but many people frequent popular sites as part of their job or at home. We also have so many connections throughout the Corvette community, that if something good or important crops up, someone is bound to bring it to our attention.
OK, so that sounds like a ton of input, how do we sort though it and decide what to implement? The core group responsible for managing the whole Corvette program consists of about 20 people from different functional areas (Program management, engineering, marketing, purchasing, finance, service, quality, manufacturing, etc.). We are a tight knit group who spend a lot of time together at work, after hours and on the road for various Corvette events. We are constantly talking about what to do that would make customers happy. Many things can be rejected or accepted quite quickly with a minimum of analysis. Others take a long time and requires that we involve our supply base. Typically a business case has to be prepared that shows whether it is worth the investment in engineering development and tooling cost. There is no one person who you would say is the keeper of the suggestion box, but the closest to that would be our Program marketing manager, Harlan Charles. He has the lead role and responsibility for defining customer features. Also worth a special mention are our people from interior and exterior design. Since part of our annual product introduction includes appearance packages, new colors or new wheels, Design is always on the lookout for a cool trend our customers might appreciate.
Part of our job on the program team is to not only sift though product ideas and assess them for viability, but convince the larger organization that those ideas are worth pursuing. In a world of finite resources, that is always a challenge.
Finally, to your question on how long does it take to implement: It varies tremendously. Simple things with minimal technical risk can be done for the next model year. These are rare. Even new colors take a long time to develop and validate. Some good ideas take longer than to do the entire car. A good example of this is our performance data recorder. We had that idea at the start of C7 but since that is not a traditional vehicle feature, it took a long time to organize and execute, so it came out the second year of production.
Tool Hoarder asked: First line of the track prep guide states "Vehicles without Z51 package should not be used for track events and competitive driving." I Notice it doesn't say cannot be used... I track my cars so got a Z51. However, I know a lot of folks who buy base cars and like to do 1-2 weekends a year in HPDE1. If the car were to suffer a mechanical failure would coverage be denied? I understand if the car suffered overheat issues and/or brake fade issues. Thank you
Tadge answered: This is a tricky one, Tool Hoarder. You are delving into a gray area where everything depends on the specifics of any particular vehicle use.
Let me start with the basics.... Corvette is a sports car. Why don't we just harden them all for the track to avoid this question? The truth is many customers use their Corvette for road driving only and we don't want to penalize those owners unnecessarily. Aside from cost and mass, making our car "track certified", has other trade-offs. We have had a lot of customer interest in more well-rounded rubber. We have had a great reception for our ultra-high performance all season tires. Nobody likes brake dust, but unfortunately the aggressive pads we must use for track durability and performance throw off some dust. That means cleaning your wheels more often. Also, our standard pads are compatible with rotors treated for reduced corrosion. The Z51 pads are not, so the rotors will have more tendency to show some cosmetic rust if the car is not driven. Then there is efficiency: Low drag is achieved by routing air cleanly around the vehicle. Taking air and running it through a tortuous path to get more air on the brakes adds drag. Forcing air through finned heat exchangers adds drag but it is the only way to keep engine, trans and A/C temps under control on a hot day at the track. Front splitters and rear spoilers add down force, but they add drag too. Our Z51 option has a lot of content precisely because it takes all of it to keep the car performing great the hands of a pro driver on a 100-degree day. Some third-party reviews have already validated this performance lap after lap, tanks of fuel at a time.
So, do we just not care about non-Z51 performance? Of course not. The standard Corvette must be a great sports car. We design it for very well-rounded performance, and it can still be driven very hard and fast. The reason we do not recommend it for the track, is that the driver may notice a few things because it wasn't optimized for that usage. All season tires don't use the rubber compounds that can stand extended periods of high-stress, high-temperature use. Therefore, you may get accelerated or uneven wear. As you mention in your question, brake fade could become noticeable as well and this is one area where the C8 driver needs to understand the effects of the cooling airflow balance I described above. With our electro-hydraulic apply system brake fade will appear both in higher pedal effort and in progressively more intrusive warning messages to the driver. Eventually the vehicle speed will be limited if brake pad or rotor damage is occurring. If the early warnings are ignored and the car is pushed to this speed limitation it will need to be serviced at the dealership prior to going back on the track. The car’s powertrain will act to protect itself, so mechanical failure is unlikely although the driver may notice performance pullbacks as the car senses impending thermal stress. For the 2020 Stingray we made a dry sump engine lube system standard ensuring an extra measure of confidence in that area. Bottom line is that most people would not have any serious issues driving an FE1 (non-Z51) car on the track, but GM does not recommend it because the car is not equipped or validated for that use. There are also variable driver skill levels as well to consider. That is why it is a grey area. Thanks for the question.
ZR1Bob asked:
Curious why the C8 requires 7/8" lug nuts and 140 ft. lbs. of tightening torque up from 13/16" and 100 ft. lbs. for the C7 --Bob
Tadge answered: Thanks for the question ZR1Bob. Our move to a mid-engine architecture shifted mass rearward so that the Corvette's weight distribution is 40F/60R. We take advantage of that traction with more torque multiplication through our new DCT for improved acceleration. The wheel stud size, pattern, and stud count is based on the needed wheel attachment clamp load to account for vehicle axle load, tire grip and other loads that the wheel-to-bearing joint must endure. These calculations drove us to the M14 wheel stud size for the rear axle. Many generations of Corvettes have used 5 studs on a 4.75 inch diameter bolt circle. It was a very standard pattern for the industry. For this generation we are moving to the metric standard of 5 x 120 mm. This change has nothing to do with the loads, in fact they are very similar patterns. So much so, that some people may try to use wheels designed for one pattern on a bearing with the other. That is very ill-advised. I'm glad this question has been asked because we need to let people know about the potential mismatch problem.
Although not needed for loads, we elected to use the same design on the front axle to keep a common lug nut, similar bearing design, and aesthetics.
Why not include a transmission factory fill of the 2L necessary to make the transmission track reliable under hard driving conditions? Or make it an extra cost option. I would much rather pay to have proper fill for the track easily added at the factory rather than make the dealer pull the trunk, air cleaner apart to add the 2L of the correct transmission fluid.
Tadge answered:
Hi GTS Bruce. Like many of the questions I answer on this forum, the answer involves tradeoffs that might not be obvious. Ideally, we would customize each car to the customer's intended use. We have to be mindful of driving huge manufacturing complexity and cost into all cars because we are trying to keep the Corvette as affordable as possible. This question, like other track-prep questions, involve balancing the needs of the time the car spends operating on track versus the majority of time it is driven on the road. If we added the extra trans lube to all cars we would be penalizing all cars with additional cost, mass and reduced fuel economy. The fuel economy reduction is small, but quite measurable and affects our label values, GM's CAFE status and the real world economy. Your question recognizes this problem by suggesting that we only over-fill the transmissions by customer request. This is where the manufacturing complexity comes in. We don't fill the transmission in Bowling Green. We receive the transmission from Wixom, Michigan where it is fully assembled, filled with oil and made ready to install in a car at BG. There is no variable-fill equipment in Wixom that could customize lube levels and if we did have, we would create different transmission part numbers based only on the amount of oil inside. Outside the transmission would look identical creating an error-proofing challenge. So, what is so hard about toping off the trans on the line at BG? Handling specialty lubes inside our plant requires complex fill equipment with elaborate environmental and safety protections. Many of these are required by law. Impossible? No, just expensive.
I appreciate the question and acknowledge the request from you and other customers intending to track their cars. The good news is that we don't recommend that you remove the excess oil when you head back to the street. There is no harm other than the small fuel economy penalty. We pride ourselves on the Corvette team on listening to our customers very intently. We will take this input and see if we could incorporate some sort of custom fill in our process in the future.
11-15-2018, 03:28 PM
Oil life monitor calibration same for dry and wet sump?
