Ask Tadge: Answer Thread - Page 3 - CorvetteForum - Chevrolet Corvette Forum Discussion

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 10-03-2016, 11:57 AM
  #41  
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Default 2017 Z06 Changes and Improvements

The original answer is here.

jvp asked:
Many of us saw the new 2017 Z06 on display at the Carlisle, PA show this past weekend and heard from various attending GM folks about the changes. Could you provide us with the full hardware details on the 2017 Z06 changes and the expected performance improvements?
Tadge answered:
For the 2017 Z06 we have modified the intercooler geometry quite substantially to allow improved cooling of the intake charge to all cylinders in the LT4. This will reduce the likelihood of detonation and retarded spark timing which in turn reduces engine output. In prior years that was typically the first sign of thermal stress under heavy-duty track work in very hot ambient temperatures. In addition, for manual transmissions, we have adapted the horizontal, “lay down” cooler used to remove heat from the automatic transmission for additional cooling in the engine coolant circuit. The extra cooler, plumbed in series with the radiator, as shown the diagram below, lowers coolant temperatures about 18 degrees Fahrenheit. Since we use coolant to extract heat from the engine oil in a dedicated heat exchanger, the engine oil temperature is lowered similarly.



Unfortunately, the horizontal cooler is still needed to remove heat from the automatic transmission cars and so can’t be used for this purpose. In our testing of the new set up in the manual transmission, pro-level drivers can run a full tank of fuel in temperatures of up to 100 degrees, a substantial improvement over prior years. Obviously, performance is highly dependent on driver skill and style. Most drivers will see no issues even at temperatures well above 100 degrees. The automatic transmission car can be driven on the track and is improved for 2017. But, because we need the lay-down cooler for trans lube cooling, the automatic’s performance is not improved as much as cars with the manual trans. As a result we are not claiming full-tank-of-fuel robustness above 85 degrees.

We will be working on continued improvement of the automatic transmission vehicles but, for now the best choice for customers wanting durable performance in high temperature, hard-core track work is the manual transmission. Torque converter automatics have inherently more heat rejection and will always lag manuals in thermal robustness. Just be clear, neither transmission has an issue in normal street driving, auto cross, or road course work at lower temperatures.

We are putting together plans for kits that would enable prior year owners to update their cars. More to follow on that. But, just to reiterate, those kits will do absolutely nothing for customers who drive their cars on the street. There is no horsepower change or other performance improvement.

Last edited by jvp; 10-03-2016 at 05:12 PM.
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Old 10-13-2016, 10:27 AM
  #42  
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Default Cold Air Intake

The original answer thread is here.

Rookieracer asked:
It seems like the aftermarket industry has found quite a lot of power with the various cold air intake systems. More than I would normally think possible on a modern day hot rod like the Z06.

Would you please share your thoughts on the possible restriction of the air intake system on the Z06 models versus the base models?
Tadge answered:

The induction systems for the Stingray, Grand Sport and Z06 are essentially identical. The only difference is that the supercharged engine has an off-center location for the throttle body that necessitates a different plumbing geometry downstream of the filter. Although one person on the thread speculates that we commonized the filter elements to save money, that is certainly not the case. We engineer all Corvette intake systems for minimum restriction and to meet many other requirements that aftermarket companies do not.

We do not routinely test aftermarket induction systems or any other aftermarket parts for that matter. We have our hands full designing, building and testing our production hardware. Although simple in concept, induction systems play an important role in many vehicle performance areas. Aside from the exhaust, there is no greater noise source on a performance vehicle. Induction systems generally have many tuning elements that ensure the quality of the sound emanating from it are pleasing and harmonious with the exhaust note. These tuning elements also dampen the sound energy to help with pass-by requirements. Aftermarket companies don't have to worry about it, but as the OEM, we must guarantee that our products are quiet enough to be driven at full throttle by a microphone by the side of the road and meet certain decibel levels. There are pass-by laws in many states and pretty universal around the world.

Another important element in the induction system is the mass air flow sensor or MAF. Engines can only run at their optimal efficiency if they have very precise data on the amount of air flowing into them. Although most people think of air flow into an engine as fairly continuous, it really is not. The opening and closing of valves and reciprocating nature of internal combustion engines means the air flow is really a series of pulses which make measuring the exact flow challenging. Intake engineers spend a lot of time optimizing the system to get excellent signal quality out of the MAF. In addition to efficiency, or fuel economy, the precise metering of air and fuel is directly correlated with tail pipe emissions, an area of extreme scrutiny by government agencies for we manufacturers.

There are some other areas of intake design that you might not think about right away such as water fording. We do tests where we drive the car at various speed through water troughs of depths between 2 and 12 inches. Most customers would never dream of doing such a thing, and, although I don't recommend it, we take due care to make sure the engine does not ingest water. In fact, as we get to the end of the trough, we go wide open throttle to maximize the suction into the engine. In case anyone is puzzled about why this is important, when an engine ingests water into the cylinder, it can hydro-lock resulting in complete engine failure. Most customers would return to the dealer and ask for engine replacement under warranty. This is one of the reasons installation of aftermarket intakes can void your powertrain warranty. In addition to water fording we do validation testing for extreme rain, snow and dirty environments.

Besides needing to be fed dry air, the induction system needs access to cool ambient air. This is why we breathe into a space behind the headlamp and under the right fender. The air inside the engine compartment is generally much warmer and, even though a larger, lower restriction filter could be packaged there, the hot air ingestion outweighs the filter restriction in terms of real world performance. Now some companies might make this choice and then optimize the dyno set up to minimize the effects such as running with the hood open or a strategically placed external fan. I have no specific knowledge about how the aftermarket companies operate, but I do know that dynos can be set up in many ways to demonstrate performance improvements that do not materialize in real-world driving.

The air filter itself is the focus of many discussions on low restriction. Its job is to keep foreign material out of the engine. Here again, there are many trade-off decisions balancing restriction with filter life (service interval) and filtration quality. Sacrificing either of the latter two improve the former. We tend to be conservative to make sure that our engines are very durable, so that does open up an opportunity for aftermarket system.

As with many of the questions on this forum, all vehicle design is a balance of trade-offs. We do what is legal and right for the vast majority of customers. Aftermarket companies offer products that strike a different balance that might appeal to some folks. I am appreciative of this opportunity to explain some of the thought behind the decisions we make.
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Old 10-31-2016, 12:35 PM
  #43  
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Default How are Colors Selected for Corvettes?

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Reason222 asked:
I'm curious to know what kind of process goes into choosing the colors that will be available for Corvettes. I may be the odd guy out, but I feel like the colors available for corvette tend to stay pretty generic. I'm sure Black, red, gray, white and blue are your biggest sellers and kind of standard. Why not use some of the extra color "slots" you have available to use something more vibrant and interesting.

You could make a lighter green, lime green, or a lighter orange, or a lighter shade of purple. Sure they might not be high sellers, but that's what your "standard" colors could be for. Why keep changing the shade of gray, or having multiple reds? Is the market you're missing for these lighter, more vibrant colors not large enough to offset the cost? or is there some other force that keeps corvettes in dark shades of pretty much everything.


Tadge answered:
Interesting question Reason222.

As your question reflects, customers are extremely passionate about color choices. We have an entire department here at GM dedicated to the determination of interior and exterior colors for all our vehicles. They study color trends around the world in automotive, housing, interior design, fashion clothing and other areas where color plays a role in customer delight. As you point out, there are some preferences that have reliable demand and other colors that are more "faddish", meaning they get hot for a while and then disappear. It would be a lot easier if we could pick a palette of interior colors and exterior colors separately. But they have to go together. We have seen some killer interiors that just don't look good with many of our exterior colors. So one of the challenges is to make sure we have many great combinations, not just great standalone colors. Despite all the new exciting colors, our top sellers are the three oldest colors in the palette: Arctic White, Black, and Torch Red. These are classic Corvette colors and we have learned from experience not to mess with them. These are staples and will continue to carry-on. The Blade silver is also a must-have for a sports car and our Corvette Racing Yellow is linked to our successful C7.R racing program. Recently we introduced four new colors. Two are inspired by historic colors: Admiral Blue and Black Rose. The other two colors are all new: Watkins Glen Gray and Sterling Blue. We always try to make sure we have a mix of conservative colors and expressive vibrant ones.

Another factor we consider when choosing a color is making sure it simply looks good on the body. Many colors that may look striking on a color sample simply don't translate into an attractive package on an assembled Corvette. By picking colors that accentuate the Corvette's crisp lines we can enhance the overall design theme. When incorporating metallic paints we consider how the color travels as it flows across the curves of the car's body. With a paint that demonstrates this color travel or flop (these are industry terms for a color's variation in hue when light is reflected off the painted surface at differing angles) we evaluate the finished product to make sure it is still appealing when viewed from different directions. By incorporating a tinted clear coat with some of our colors, we can add a depth and richness that is not readily possible with a basecoat alone further enhancing the beauty of the vehicle.

The reason we put so much effort into choosing colors is that it is an expensive, complex process to put a new color into production. Most customers assume we just order paint from a supplier and paint the car, but it is not that simple. Automotive paints are highly engineered chemical mixes that have to meet very challenging requirements for adhesion and durability in addition to looking pretty on all the different substrates (panel materials) we use. Every new color must spray out evenly and provide a consistent finish over the entire panel on every Corvette. Because Corvette is a composite car, every paint color we use is custom mixed for us. We do not share paint with any other car in the world. Even a standard color like black is unique for us. Paint color is not only sensitive to the substrate, it is highly dependent on the process used to apply it. Lengthy trials are typically required to get the color and quality right. Panels are painted over and over resulting in a lot of scrap material (cost). In addition to the work done in Bowling Green, all our suppliers from whom we buy painted parts (like mirrors) have to work their processes so the parts match perfectly. Once we have a color in production, managing low volume colors becomes problematic. Since the same robots paint every car, we have to clean the system delivering the paint to the robot every time we have to paint a different color. That is why when you visit Bowling Green you will see many cars of the same color coming down the line in a row - We group like-colored orders together. When the penetration of a color goes below 5% the costs become unmanageable so we look to replace it with something more customers will choose. We have done a lot of great colors that many people really like, but unless it is their favorite over all the others, it doesn't sell. A lot of people love Corvettes in yellow but in spite of the fact that the C7.R is yellow, few people actually buy it (Don't worry, even though it is a low volume color, we have no intention of getting rid of it any time soon).

Thanks very much for the question. We are keenly interested in picking colors our customers will love. Right now the trend is towards more expressive so your sentiments are in line with the way palettes are moving. I should also mention that our new paint shop currently under construction at our Bowling Green Plant is installing additional technology that will allow for expanded color choices in the future. Look forward to more exciting colors coming soon!
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Old 11-10-2016, 04:48 PM
  #44  
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Default Spats, Protective Film, and Splash Guards

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grcor asked:
Can you please tell us why you are not molding the fenders to eliminate the need for spats, protective film, and splash guards?
Tadge answered:
All Corvette exterior features and surface shapes are designed for maximum performance and great aesthetics. Around the front wheel openings, both the C6 (Z06, GS and ZR1) and C7 (GS and Z06) feature what you are calling spats arcing down the forward edge. These features create high pressure on the front/top and low pressure on the back/underside resulting in down force and evacuation of hot air from the wheel opening. The aerodynamic studies for both C6 and C7 independently proved their value. To work, they need to be a very specific shape - specifically a sharp break in the surface where the spat meets the fender. I have been asked many times why we couldn't just form that shape from the front fender so it would be all one painted piece instead of looking "tacked on". We looked at that and decided it looked pretty bad when painted bright colors. Your eye is immediately drawn to that feature and it does not look integrated or graceful. Naturally the question is, "If it is so important, why don't we see it on the C7.R race car?" The reason is that the race car sits so low to the ground it can take advantage of even more efficient aerodynamic features such as an "underwing" that sits beneath the front splitter. "Ok, then why don't we see it on other street cars?". Well, actually you do. There are several, typically very serious performance cars that have similar features such as the Porsche GT3RS.



On the question of why we don't pull the fender behind the tire outboard to completely cover the front tire, there are several reasons for that. The main reason is aerodynamic drag. The air flowing by the side of the car wants to re-attach to the smooth part of the body rearward of the wheel opening. The lowest drag cars in the world actually have a very large radius on the body surface making up the transition from the wheel opening to the body side. Bringing the corner of the bottom of the fender out flush with the outside of the tire creates a stagnation point for the air which generates high pressure on a forward facing surface - drag. That same forward facing surface also makes a perfect target for stones coming off the tire... It gets hammered. So most companies choose to bring that fender corner inward a bit and put some radius on it. Others add what looks like a small mud flap.

Stone throw mitigation is actually an interesting science. With slow motion video we know that many stones don't take the obvious path straight off the tire and into the body side. Some bounce between the underside of the car and the roadway more than once before contacting a part of the car where you might notice the damage. I mention this because the premise of this question is that we can solve the stone throw problem with fender shape. It is true we can help it at the cost of drag, but can't solve it completely.

The last point I would make is that the Corvette is a relatively compact car with massively over-sized tires. Like many sports cars around the world, the architecture and aesthetic choices give the car a very aggressive look. For decades the "coke bottle" shape has been a Corvette hallmark. We could help stone throw by making a slab-sided car with the body skin pushed out to the outside face of the tires, but it would look like a refrigerator on wheels. Instead we typically pull the body skin in as tautly as we can over the mechanicals giving it the lean, muscular shape most people really like.

Last edited by jvp; 11-10-2016 at 04:50 PM.
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Old 12-09-2016, 01:20 PM
  #45  
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Default Track performance GS MRC vs Z51 with T1 Suspension

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C7fasttoy asked:
I would be interested to know in between GS non Z07 and Z51 with T1 suspension which would have better track performance assuming both using same tire despite the fact GS has some advantage due wider tires.
Tadge answered:
The short answer to the specific question asked is, “The standard Grand Sport and the Stingray fitted with T1 hardware would be expected to have very similar capability on the track”.

But you were probably hoping for more than that.

Since the packages were developed independently of each other and at different times by different engineers we don’t have a lot of direct comparison data. Ideally we would run both cars on the same track on the same day with the same driver. The data we have is from our on-site Milford road course – a track few customers will ever drive. The T1 package was developed around the SCCA spec tire, the Hoosier A6. Since the tire was the starting point for chassis development, we had to optimize the rest of the components around the performance of that tire. The best solution included a very large stabilizer bar on the front and in the rear we used the same bar we would eventually spec on the Grand Sport. This bar combo gave us the roll gradient we wanted and very balanced handling at the limit. We wanted to make sure the cars had performance accessible to many drivers.

There is a question in the thread wondering why higher spring rates were not specified. We looked at that, but found no significant performance benefit, and in fact, are within 10 % of the C6 T1 spec (front slightly softer, rear slightly stiffer). Shock tuning migrated towards calibrations we loved on the track in development work for the Stingray Z51, but were not put in productions because the street ride was considered too harsh for most customers.

OK, how about some numbers…. Well, here is the best we have. On our track a Stingray Z51 has run a 1:56.3. With the T1 package we have a time of 1:53.9, an almost 2.5 second improvement. To be honest, we didn’t put huge energy into setting the fastest possible time on a track that is not comparable to others, so there could be a few more tenths in it. Ditto the standard Grand Sport – the times are right in that range, but we spent most of our track time with the Z07 package. Our best time with that set up is 1:52.6.
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Old 02-03-2017, 04:15 PM
  #46  
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Default Track day brake failures and warranty

The answer thread is here.

RS4EVA asked:
Many customers are reporting brake fluid leaking out of the bleed screws during track events... The brake fluid appears like it's being pushed out from the outer bleed screw, which introduces air into the system causing the fluid to boil, and the brakes to go away quickly. The inner screw and caliper seem to be largely unaffected and stay clean.

Since this is only able to be reproduced under track conditions, the dealers aren't able to diagnose or fix it. Can someone from your engineering team help by investigating the issue, diagnosing the problem and coming up with a resolution.
Tadge answered:
Many of the questions I get on this forum are from track folks who exercise their Corvette to the limit of its performance. We are very happy that people are using that capability and for the most part, there are very few problems. Our service folks and Brembo engineers regularly monitor vehicles being used on track. Properly prepared, we have had minimal issues with brake fluid leaks through the bleeder screws.

Since many people read my answers to these questions, I have to answer to a larger crowd, not just you, the specific questioner, RS4EVA. So I will include vehicle prep basics for everyone and I don't want you to be insulted, like I'm assuming you don't know what you are doing.

Although it is not always a popular answer, I can only testify to the performance of stock vehicles. We do our validation on factory spec cars. There is no way to account for the performance of the infinite number of after-market components. I talk to customers every day who swear their car is stock because they don't consider the use of slicks, racing coolant, or race brake pads to be modifications. Same with new shocks, trim height changes or alignment specs outside what is recommended in the owner’s manual. Even mixing and matching factory parts can lead to issues such as putting up-level aerodynamic components on a car with standard brakes. Adding downforce or tampering with brake cooling airflow can lead to reduced performance. Both tires and alternative pads can impact brake performance substantially. Neither Brembo nor GM can be responsible for the performance of other pad materials. Racing materials can cause elevated fluid temperatures (even boil) and accelerated rotor wear and heat checking, to say nothing of the adverse impact on the ABS and stability control calibrations.

Regarding the ‘weeping’ of bleeder screws: Typically that is the result of the person servicing the caliper not evacuating the small column of fluid (maybe 0.2cc) that remains in the bleeder after tightening. In road use this is a nonissue, but if the vehicle is taken to the track and the caliper gets hot, the fluid can expand and seep out.

The bleeder screw design and caliper interface (seat/port geometry) is nearly universal in Brembo aluminum calipers (including Brembo’s racing products) so it’s likely not design issue. Calipers are 100% leak tested for low pressure, high pressure and vacuum, both before and after painting. The bleeder screws must be properly torqued and only when the caliper is cool (very important even though it may seem like a minor thing). Keep in mind torque values are different between two-piece calipers (like JL9/J55) and monoblock calipers (J56/J57 front). Proper torque of bridge bolts in six-piston calipers that use them is also important. A squirt of compressed air or brake cleaner on the bleeder is a good idea after bleeding to purge any residual fluid that might weep.

Approved brake fluid must be used, appropriate for the intended usage (meaning DOT4 for track use). Some customers use racing fluids (Castrol SRF, Motul 600, etc) which have not been tested by GM or Brembo for seal compatibility with caliper, master cylinder or ABS unit. When replacing existing brake fluid with a qualified high performance brake fluid it must come from a sealed container. Brake fluid with a dry boiling point >279 °C (534 °F) is qualified. If high performance brake fluid is used, replace it with GM approved brake fluid before driving on public roads. If high performance brake fluid is in the vehicle and the age of the brake fluid is over a month old or unknown, replace the brake fluid before track events and competitive driving. Do not use silicone or DOT-5 brake fluids.

Finally it is always a good idea after any severe usage, to inspect dust boots and replace as necessary. Very hot temperatures can cause cracking or, in extreme cases, dust boot melting.

Thank you for the question RS4EVA. We are always interested in learning more about out hardware performance in the field. Brembo is an elite brake manufacturer, and like us, we are always interested in continuous improvement.
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Old 02-03-2017, 05:10 PM
  #47  
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Default What makes a Corvette a "Corvette"

The original answer thread is here.

Clairvoyantwolf asked:
Is a corvette a “Corvette” if instead of large displacement high torque V8 it instead came with a small displacement high revving engine of whatever configuration? Are such concerns a consideration when developing a new model or generation? And how would you characterize the corvette driving experience, especially how it relates to your competitors?
Tadge answered:
Corvette has stayed relevant for over 60 years by continually refining and improving the same basic formula: Powerful, responsive engine, intimate seating for 2, and a chassis tuned for maximum driving enjoyment. Couple that with exciting looks and reasonable attainability and you have a winning formula.

When we introduced the 7th generation car we used the words: State of the art performance technology, excellent power to weight ratio, and beautiful design. Although that mission has been consistent, the technology many details of the execution have evolved. The world keeps changing and the Corvette must as well.

Members of the Corvette team spend a lot of time with customers. We get plenty of input and some of it is conflicting. In a nutshell, we have to select the right combination of features and technology that we know will represent a good value proposition for our customers. That is the essence of our jobs. So, of course the character of the powertrain is a huge consideration when developing a new car. We have to balance the pressure from regulating bodies around the world trying to force manufacturers to do small displacement, high specific output engines with the desire of our customers who want lots of torque and the performance of a V8. Frequent readers of this section of the forum or attendees at many Corvette events around the country know we can't disclose any future product information. However you can trust me when I say we do everything in our power to right by our customers regardless of other pressures.

The question asks about the character of the driving experience versus our competitors. Our goal is a car that allows both track oriented high performance driving while also being accommodating for long road trips. We want an exotic driving experience without the exotic hassles. We want the car to be everything from a super-capable track machine and an easy-to-live-with daily driver. You could write a book on what makes a Corvette a Corvette (and some people have), but for us it boils down to creating a machine that gives many people the best possible driving experience.

Last edited by jvp; 02-03-2017 at 05:11 PM.
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Old 02-16-2017, 05:11 PM
  #48  
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Default Manual trans vs auto

The original answer thread is here.

FYREANT asked:
I am curious at how you and the rest of the Corvette team feels about the apparent decline in manual transmission vehicle production across the American auto industry and in particular, Corvette. Do you feel like the manual trans is no longer an important option for the Corvette buying market and do you think there will come a time that Corvette is only available in auto trans?
Tadge answered:
I hear this question a lot since people who love driving manual transmission vehicles are very passionate about it. Obviously there is no substitute for the level of engagement and control that you have when driving a manual. Believe me, I get it. In my 40+ years of buying and driving vehicles, I have never purchased a new vehicle for my own use that wasn't a manual trans.

Of course, the auto industry was started and for decades remained almost exclusively propelled with manual transmissions. Starting in the 1940's, automatic transmissions became available. GM, of course, was a principle change agent with the invention of the Hydramatic which signaled a sea change with two pedal cars becoming the norm and three pedal cars dropping in volume in a steady trend that continues to this day. In North America there are very few cars that even offer a manual transmission, and those that do see very low take rates. Customer preferences are changing even among sports car enthusiasts. Both the fifth and sixth generation Corvette Z06s were offered with only a manual and we heard from many customers that they would like an automatic. Now that we offer a choice, the automatic is running 80%. The value proposition for most people has shifted towards automatics. Even though manuals have gotten better with more gears, rev-matching and lower clutch efforts, automatics have gotten more engaging and capable with paddle shifters, quicker shifts than humans can make, and multiple modes of operation.

The manual transmission used to be the low cost option and therefore was standard equipment. High volumes of automatics have given us economies of scale and reduced costs. Manuals have experienced the opposite trend so now we are in a position where the traditional business model no longer works. Manual transmission suppliers face dwindling volumes making profitable production more difficult. This is why you see some companies eliminating manuals completely or packaging them in expensive models targeted towards serious enthusiasts. I don't know when, but eventually these market forces may make manual transmissions unavailable at any price, since there won't be manufacturers willing to make them. In the meantime, we are proud to be able to offer both transmission choices in all our models. Appreciate them while they are still here!
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Old 03-22-2017, 08:41 AM
  #49  
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Default GM Dealership Corvette Technician Training/Certification Process

The original answer thread is here.

slickstick asked
Is service quality and inconsistency an acknowledged issue by GM and, if so, what is being done to rectify it?
Tadge answered:
Thank you for the question, slickstick. Having talked to thousands of customers over the years, all Corvette team members are acutely aware of this concern. In addition, many of us or close family members own Corvettes and have more personal experiences with Corvette service – mostly positive but a few negative. Of course, the negative stories get far more air-play than the positive ones, but yes, this is an acknowledged issue because we hear the real-world stories.

To give everyone reading this some background: All Chevrolet dealers are independent businesses. By law, automakers cannot own dealerships, a rule Tesla is challenging in court. So, even though you can buy an Apple product in an Apple-owned store, the auto industry has been singled-out for different treatment under the law. The result is that we have limited leverage over the dealer operations. Dealers are as different as the markets they serve. For some, the Corvette is a huge part of their business and the way they operate it shows that priority. Others sell only a few Vettes a year and so don’t want to invest large amounts in Corvette service capability.

Here are some important facts to keep in mind:
  • Not all Corvette dealers are Corvette Certified
  • Certified Corvette dealers are required to keep their Sales and Service staff trained on both the product features and the technical functions of the vehicle. The training is updated each model year
  • Certified Corvette dealers are required to have all of the special tools necessary to repair the vehicle.
  • Dealers have access to all new service communications (bulletins and preliminary information)
  • Dealers are required to view Emerging Issues training. This keeps the technicians updated with the latest diagnostic information and repair procedures.

I can image the question being asked, “Why don’t you limit Corvette sales to known certified dealers with good track record for service?” We have done that in the past and we get lots of feedback from dealers and customers in smaller markets. Customers get quite upset if they can’t buy their dream car at their local dealer, someone they consider a pillar of their community and with whom they have done business for many years. The smaller dealer would like to get the customer the car, but that sale doesn’t warrant investing in the special tools and training to service the car for life.

Chevrolet has worked very hard to establish Corvette sales and service requirements for dealers. There are many very good dealers but to your point, it is not as consistent as it needs to be and is one of our focus areas as we try to continuously improve our customer’s experience. The Chevy service team works hard to send out dealer bulletins and over-communicate service procedures for Corvette. We even required every dealership to send a sales person to our official driving school at Spring Mountain to learn all about the seventh generation Corvette.

Although dealers are independent businesses, we do consider them our partners and will continue to do everything in our power to improve our customer’s experience. The effort has been paying off. Data from independent customer surveys has been getting better. In fact, Chevrolet is ranked the highest full-line manufacturer in service satisfaction by J.D. Power and Associates.
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Old 04-12-2017, 05:20 PM
  #50  
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Default 2017 upgrades for 2015&2016 model years

The original answer thread is here.

wstaab asked
Tadge we need a status on upgrades for 2015&2016 model year C7's.
Supercharger upgrades; tilted internal heat ex-changers and larger supercharger lid.
Auxiliary radiator for manual transmission cars.
Transmission cooling upgrades for automatic transmission Z06's Coolant temp as a pocket gauge in sport mode.
2017 PDR display upgrade.
Will they be available and if so when?
Tadge answered:

Let me take these in roughly reverse order starting with the cluster and PDR 2017 changes: The short answer is no, we don't intend to create a backwards compatible software set that can be reflashed into 2014, '15 or '16 models. From the outside, I can see why it would look like a simple matter to offer the 2017 software and calibrations for prior years. The truth is that it is anything but. Each year we strive to continuously improve the Corvette using hardware, software and calibrations. In cases where we simply make a cal change, it is usually backwards compatible. But those are rare. To add new features like PDR screen overlays or add a new pocket gage in the cluster requires software at a minimum. Anyone who has dealt with complex software will tell you that validating it for all situations and use-cases is not a trivial matter. The Corvette's (and most modern vehicles for that matter) electrical system consists of many complex interacting systems. Changes in one area can affect another.... Often in surprising ways. What this means is that there is usually a need for a specific software solution for each configuration. That means we would have to write and validate new code to provide the same functionality as new customers are seeing for 2017. More specifically that is a new code set for each of 2014, 2015 and 2016 model years. And if we wanted to the same thing for any 2018 changes, it gets worse with new solutions needed for 2014 - 2017. This an unmanageable demand on constrained resources when we are trying to focus our efforts on making each year better than the last and bringing it out with world-class reliability.

One area where we are going to try to offer upgrades is MR calibrations. Our magnetorheological shocks are ideal components to upgrade with calibrations because they have a large influence over the dynamic behavior of the vehicle. We have made some improvements in later models years and are planning to offer those upgrades to prior cars. Of, course it is not "free". We have to do work to check to make sure the new cal's are completely compatible with other systems such as ABS, Traction control and stability systems. More to follow on this.

The auxiliary radiator for the manual transmission has been available since last year http://www.gmperformancemotor.com/parts/84037858.html. What may be causing confusion is that it is currently on back order and is planned to be restocked next month under a new kit part number 84201727. We made some minor improvements to the hardware and installation instructions which required the part number change.

The question also references “Transmission cooling upgrades for automatic transmission Z06's”. We have a secondary trans cooler on automatic Z06’s already. The RPO is V03. It has been standard equipment on the car since it was introduced for 2015. There are no further upgrades available at this time. Based on our testing of 2017 automatic vehicles, the trans lube temperature is not typically the “weak link” on the track.

Finally, the 2017 supercharger upgrade kit: The hardware is already available piece-meal through service parts. We are working however, to assemble a kit that would make customer installation more straightforward. The kit would include the supercharger assembly, a new hood liner and a new calibration for automatic transmission vehicles (This calibration is not backwards compatible with 2015 and 16 cars but is important and is being re-developed for the earlier cars). We would like to offer the kit at a nice discount from the normal service parts cost to owners of 2015 and 2016 Z06's. Putting this all together is a fairly complex task, but we are making progress. Readers of the Corvette Forum won't have to ask me when it is available. I will post it to the Ask Tadge section as soon as I can regardless of the question being asked.
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Old 04-12-2017, 05:21 PM
  #51  
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Default Valet Mode: Why Not Limit the Car?

The original answer thread is here.

Vyper340 asked:
Why can't the valet mode also limit the performance of the car and not just activate the PDR? It is possible on some other vehicles since it is an electronically controlled feature. Given the nature of these vehicles, wouldn't it provide piece of mind for the owner to set and know the vehicle cannot be used to its capability when a feature like this is activated?
Tadge answered:
Thanks for the suggestion Vyper340.

Valet mode is a GM corporate feature shared by many GM cars. It was not developed specifically for Corvette like the PDR (which was subsequently shared by a few other vehicles). We spend a lot of time with customers, and we didn't have a lot of requests for a feature like this. Most customers abhor the idea of a stranger taking their baby out of sight (or ear shot).

Once we decided it might have some value, we explored ways to make it even better for our customers. We did the work to integrate the PDR function into it and I believe are the only manufacturer in the world to have this ability to bring back video evidence of how the car was driven in its absence. We also talked about limiting performance but that quickly escalated into massive complications. Once you involve the Powertrain, all EPA, CARB, and global emissions regulations including diagnostics now have to be validated in both modes. It would have postponed introduction of the feature quite a bit. Yes, it is possible to do and yes, a few other manufacturers have done something like it (Including us on the C4 ZR-1). Like all customer suggestions, we will carry it forward and try to implement them when reasonable and practical. Thanks for the question. All customer feedback helps make the Corvette better and better.

One interesting side note on this topic. How much performance should remain in Valet mode? Pull out too little and you still have a really fast car that an inexperienced driver can get into trouble in. Pull out too much and safety critics will say the car doesn't perform as expected so the driver may not have the acceleration expected when he or she needs it. Where do you draw the line?
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Old 04-26-2017, 02:02 PM
  #52  
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Default Manual Transmission Gearing

Original answer thread is here.

Nosferatu asked:
On the manual transmisison Corvette (C6 & C7 included), what thought goes into how the specific gear ratios are spaced? I used to own a C6 and currently own a C7; both manual. In both generations, the Z51 package has short gearing for 1st thru 3rd gear. When you get into 4th gear the RPMs drop considerably as it is such a long pull.

On both models 3rd gear hits red line at approximately 100 MPH. 4th gear then makes a pull all the way to just under 150 MPH. As speed builds, the aerodynamic drag increases exponentially.

With that said why are there so many overdrive gears? I understand using the top most gear in their respective generations as an overdrive gear for fuel economy but closer spacing to match the lower gears would have likely gained better acceleration in the 100-150 MPH range.
Tadge answered:
Good observation, Nosferatu. A true "gearhead" question.

Before I worked in car design, I assumed that transmission gearing would be a lot like gears on a bicycle - you could match a set of gear teeth and get most any torque multiplication you wanted. Automotive transmissions are a lot more constrained. For several generations we have used 6 and 7-speed boxes from Tremec. There are few manual transmission suppliers left in the world and Tremec's unit is the one that fits best in a Corvette and is durable behind our engines. If you study all the ratio sets we have ever used with that transmission, you will notice that 4th gear is always 1:1. That is a foundational aspect of the transmission's architecture, essentially a fixed gear that we have to work around.

Gear selection involves a balance of performance, fuel economy, driveability and other metrics. Typically the standard car is biased towards taller ratios, better fuel economy and easy driveability. On more serious performance models we get more aggressive with the ratios to get higher performance off the line, better 0-60 and 1/4 mile times and quicker lap times on auto cross and most race tracks. If we could change 4th gear and get more even drops, we would, but that is just not possible. In the end, we decided not to ignore the performance potential of aggressive gearing in 1st - 3rd just to avoid a larger than optimal drop on the 3-4. Fifth gear is rarely used on the track but the major considerations there are optimization for top speed and end-of-straight speed at the Nurburgring.

Another way to accomplish the same end is to change the final drive ratio in the differential. Here again there is no free lunch. We use a variety of final drive ratios from 2.41 - 3.42 with the manual at 3:42. We already spec at the aggressive end of the range for all manual transmission cars. Why no 4:11, or more aggressive gear set? Durability and packaging. The final drive ratio is set by the relative size of the ring and pinion gear. To get more ratio, we would have to go down in pinion gear size or up in ring gear size. Smaller pinion gears are just not durable enough to stand up to a life in a Corvette. Larger ring gears make the whole differential larger, adding mass and making the whole transaxle longer. Since the location of the transaxle in the rear is pushed as far forward as it can be already, the impact of a larger differential actually make the wheel base and whole car longer! That would add even more mass. So you see, as usual, what we have in production is a carefully selected balance of competing constraints.

The question also specifically refers to "overdrive" gears. From a technical standpoint all that means is that the ratio is less than 1:1. Architecturally our manual transmission must have all gears above 4th as overdrive gears, but that is not a bad thing. Theoretically you could have a transmission with all overdrive gears and still have a perfectly driveable car - you would just need an extremely short final drive ratio. Mechanically, that is not practical or efficient so you don't see it in production on any mainstream cars.
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Old 05-12-2017, 07:07 AM
  #53  
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Default Track Testing/Validation

The answer thread is here.

Clairvoyantwolf asked:
It was mentioned in a previous Ask Tadge response that the Corvette Team had never tested at Willow Springs, and after testing there the "Rough Track Calibration" was created for the Magnetic Selective Ride Control. What tracks does the Corvette Team regularly test at and what unique insights does each venue bring?
Tadge answered:
There are hundreds or tracks in North America and perhaps thousands around the world. We pick tracks based on more variables than most people would imagine. Here are a few:

Availability: Most track owners want to keep the facility as busy as possible so booking can be a challenge. We need to find tracks that have openings when we believe we will have a vehicle ready to test. So we tend to reserve time well ahead based on long term planning. Weather plays a role here too. We don't get a lot of second chances to test based on our tight timelines so the weather outlook based on the time of the year has to be good.

Facility particulars: Quality garage and work spaces are important since much of our work involves on-site data analysis and mechanical and electrical work on the cars themselves. Product security can be important too - We are often testing vehicles that have yet to be announced.

Distance from Michigan. Our "home base" for development work is Milford, Michigan. We test there year 'round, but track work cannot be done in the Winter. Traveling great distances to find warm weather tracks is inefficient (cars sitting on a truck are useless assets) and expensive.

Historical testing data: Once we start visiting a track with some regularity, we accumulate an enormous database of vital statistics. Having those reference data is extremely valuable as we assess new model's performance vs older cars. When you are in the business of continuous improvement, high fidelity historical data is mandatory.

Of course the point of this question is the character of the tracks themselves. Each track will have unique characteristics that challenge the vehicle dynamics in different ways. A car optimized at a single track will likely perform poorly at certain others, so over the years we have developed a portfolio of testing venues that do a good job of helping us develop a well-rounded car that performs quite well at almost every track. Obviously this is not a perfect science as the Willow Springs example shows. We put together a list of our most frequently used tracks and the learning from each. We do occasionally use other facilities, but the vast majority of our testing occurs on those listed here:

Our home track, the Milford Road Course: The MRC has a remarkable density of corners. The car is rarely going straight. Also, almost all the turns have elevation or camber changes mid-corner. It was intentionally designed this way.... We tried to bring the most challenging sections of the most challenging tracks around the world together in our backyard. As a result, we can make very good predictions about how the car will behave on tracks our customers are likely to run. The correlation is especially good between the MRC and VIR (also pretty good with Road Atlanta).

Virginia International Raceway: VIR is our primary outside development track. Some of the unique features here are the high speed S's which have significant elevation change and rapid throttle movements at very high speeds. These S's combined with many lower speed corners make this a very diverse track that helps us develop both suspension, braking and chassis control systems.

Road Atlanta - Road Atlanta provides a couple steady state higher speed corners which allow us to do more thorough aerodynamic tuning. It also has a very long straight to challenge powertrain robustness.

Willow Springs - Willow is now a priority and has the fastest average speed of any western track. Turns 8 and 9 are well over 100mph and are the best opportunity we have to spend time working on aero tuning. It also has a pavement texture that is unique to the west coast that requires unique compromises to suspension calibrations.

Spring Mountain - Spring Mountain offers two main track configurations. The older 2.2 mile is very good for lubrication robustness with two long duration corners in quick succession. These corners are so good for lube system testing that we duplicated them on the MRC. Their East course provides very high brake energy and is used for brake thermal development.

Laguna Seca: The famous Monterey track provides a similar surface as Willow Springs but with much slower cornering speeds. It is challenging to Performance Traction Management (PTM) calibrations and MR tuning. It is the highest brake energy track we have ever used for testing.

Grattan - As well as being close to the proving grounds, Grattan provides a well-controlled jump where we can calibrate ABS and MR behavior with the car fully in the air. We duplicated this jump at the MRC as well.

Nurburgring - We use the Nurburgring since it has more road input (bumps, crests, dips, jumps, camber changes, etc.) and more high speed corners than any other track in the world. Obviously it's length is unique but even if it were shorter it would provide tuning opportunities that can't be found on any other racetrack in the world.

One might also wonder why we don't use the recently opened National Corvette Museum Motorsports park. Corvette Racing has already tested there with good results so we may add it to the menu someday. In the meantime, it has been received very well and is quite busy already!
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Old 06-09-2017, 02:51 PM
  #54  
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Default Why can you not just disable the AFM?

The original answer thread is here.

mountainears asked:
Why is there no option to just disable the AFM / V4 mode on the cars.
Even if it reset and had to be selected on each start up, the driver should have the choice to turn it off completely.
Tadge answered:
I am going to start by assuming this question pertains to automatic transmissions only since AFM is turned off in all modes except Eco on the manual. I also assume folks know that when the auto is operated as a manual (i.e. "M" mode on the shifter), AFM is not operational.

As with many things in automotive design, we are not free to simply engineer cars to what each customer might want. We have many other constraints. Government regulations play a huge role in how we execute vehicles. Automobiles are the most heavily regulated consumer product in the world with every major economy in the world governing their design and sale in various ways.

Although it may seem like a simple matter to have a " turn off switch" to allow customers to choose between maximum efficiency and full time V8 operation, it is not. We use AFM (Active Fuel Management, or 4 cylinder mode) to enhance fuel economy under light load conditions. It only takes 12 - 40 HP (depending on model and speed) to push a Corvette down a flat road at highway speeds. Producing that small amount of horsepower with all 8 cylinders firing and then practically closing the throttle is not as efficient as running on 4 cylinders with the throttle blade more open. There are very measureable real world economy benefits in addition to fuel economy label, federal fuel economy standards (CAFE) , and gas guzzler tax benefits. The EPA sets the fuel economy and greenhouse gas emissions test procedures for our cars. They are very sensitive to possible customer "work-arounds" that would let customers quickly and easily by-pass efficiency mechanisms. There are even special test protocols that keep manufacturers from claiming a fuel efficiency performance that few customers will actually see. The way this is done is to require testing in a variety of the vehicle modes that customers are likely to use. If there is any question, manufacturers are required to actually survey customers to find out which modes they are using. Test procedures have also gotten more conservative to lower label values in response to customer complaints that they can't achieve the fuel economy printed on the label. This has not been an issue on Corvette, but we have to follow the new procedures along with all other manufacturers. That is why you have seen fuel economy label reductions even though the car hasn't changed.

OK, so if customers demanded it, could we put in an "AFM off" switch, and just let the label values and gas guzzler taxes fall where they may? We could, but that is where CAFE (Corporate Average Fuel Economy) becomes an important consideration. General Motors must achieve fleet average fuel economy targets or face stiff financial penalties from the government. It is true that Corvette volumes are but a small part of GM's total fleet, but every tenth of a mile per gallon matters when trying to balance the entire fleet. Further complicating Corvette's contribution to GM's fleet average is the fact that fuel economy regulations are a function of a vehicle's size. The fuel economy target is set based on wheelbase multiplied by track width (if they are different front to rear, you use the average). In the eyes of the government, Corvette is a very small car. It has a compact wheelbase and even though it is fairly wide, the track width is narrow because it has wide tires and track is measured at the tire centerline.

I hear from many customers that they are happily surprised with Corvette's fuel economy, especially on long trips. The Corvette is often the most fuel efficient vehicle they own. So even though the Corvette gets outstanding fuel economy given its performance potential, that doesn't help us on corporate CAFE. As far as the regulation is concerned, based on the vehicle's size, the target fuel economy is about 40 mpg - and that is combined, meaning average city and highway. Because of this, Corvette does have an important effect on our fleet average. We have to do everything in our power to minimize the penalty. That is why we use AFM everywhere we reasonably can on the automatic transmission which is about 80% of Corvette sales.

Of course these trade-offs are nothing new. We have used skip-shift on manuals for decades despite some customer's preference against it. Most of our competitors now have start/stop. Start/stop is not so bad in a traditional car with a quiet idle, but for cars where the engine has a lot of character, it can be very disconcerting to have the engine stop every time you come to rest. Customers have expressed extreme distaste for that feature on a Corvette and so far we have avoided needing to implement it. So, like many of the questions I'm asked, it comes down to how we must balance tradeoffs. We know what customers want and do the best we can to minimize any negative implications arising from government requirements.
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Old 06-28-2017, 01:10 PM
  #55  
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Default Run-flat, EMT, ZP Tires

The original answer is here.

[email protected] asked:
Could you tell us about the evolution of run-flat/ZP tires, the reason why they are standard equipment on Corvettes, and the challenges faced from an engineering stand point?
Tadge answered:
Good question, Nate. Your thumbnail history in the question is quite accurate. I was working on C5 in 1993 when we did not know how well the extended mobility tires would work in the field or be accepted by customers. Most people appreciate the extra luggage room afforded by not having to carry around a spare tire all the time even though it is rarely used. But for a relatively compact car with large wheels and tires, the important issue is where do you put the that big rear wheel you took off after installing the space-saver spare? It would be quite unsatisfactory to have to leave the wheel behind, especially nice Corvette wheels. One of the reasons the C5 had such a large trunk with a deep center well, was that we still had to package for a removed road wheel. To accommodate that deep well, we had to design for less muffler volume than we would prefer. Low volume means increased back-pressure and less tuning flexibility for sound quality.

Many manufacturers use a sealant/inflator kit as an alternative to a spare tire. It saves room in the trunk and you don't have to carry a replaced wheel in the car. As you mentioned, we did that for the C5 Z06. The feedback we received on these kits from our Corvette customers was mixed at best. The sealant may not always seal 100% and it is only a temporary solution as we recommend that the punctured tires be inspected and permanently repaired. I found myself stuck roadside with a flat once in a C5 Z06 because I couldn't get it to seal. The sealant is only effective with punctures in the tread area up to a 6mm diameter and it cannot repair tires with punctures in the sidewall. At that time the sealant also interfered with the tire pressure monitors (mounted on the valve stem) that customers really like. Obviously, there are lots of personal safety reasons we do everything possible to keep our customers from being stranded. The sealant did provide many customers the ability to continue their drive to where they needed to go, but we believe the zero pressure tires are a better solution for Corvette customers.

When Extended Mobility Tires were first introduced on the C5, they were very conservatively designed. Goodyear wanted to make sure that the zero pressure performance was good both in terms of vehicle handling and flat tire mileage. The compromises you cite were very obvious in those days because the tire sidewall had to be designed stiff enough to support the weight of the car. Since then, technology has advanced considerably for both run-flat and conventional tires. Corvette has essentially the highest performance street tires in the world. Together with Michelin, we have been pushing the performance envelope far beyond what many thought possible with street tires. We have worked with them extensively to minimize the mass and ride penalty to get ZP performance we need. The truth is, even without ZP capability, a conventional tire needs very stiff sidewalls to manage the lateral loads and our required steering response. So in the realm of super high performance tires, the designs for ZP and non-ZP have converged to where the mass and ride penalties are very small. The same is also true for noise and cost. Tires are the single most important component in vehicle handling performance. We and Michelin pay a lot for development and construction, making every effort to offer the best performance tires in the world. Conventional or ZP, they would cost more than lesser performing tires.
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Old 06-29-2017, 05:51 PM
  #56  
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Default Characteristics of Brembo Calipers

The answer thread is here.

spearfish25 asked:
How do the Z06 Brembo brake calipers compare to Brembo's retail offerings? Are the calipers altered or engineered by GM in any way to tailor them specifically to the Z06? Are there any specific differences between the OEM supplied Brembos and the retail versions?
Tadge answered:
Most questions I get are specific to the Corvette design as we build it in Bowling Green. This one is asking about comparing our factory design vs an aftermarket execution. Since we (GM) don’t routinely test or evaluate aftermarket hardware or software, I usually can’t offer any assessment. In this case, Brembo is the supplier for both the factory and the aftermarket hardware, so I have asked them to provide the response:

While the Corvette Z06 brakes and Brembo High Performance (retail) brake kits may appear similar, they are actually very distinct products. The Corvette calipers and discs were designed from scratch to meet the specific requirements of GM Engineering and the Corvette program team:
  • Direct compatibility with all suspension hardware and a variety of production wheel profiles
  • Robust product performance and durability, validated to a multitude of GM test procedures including extreme environmental conditions, life-of-the-car durability and consistant all-around braking performance for both track and street
  • Reasonable levels of noise, dust and wear—an area where considerable development is done
  • Specific paint color options which match or compliment the Chevrolet color range
  • Compliance with US Federal Motor Vehicle Safety Standards for production vehicles
Even though the Corvette is relatively low volume, it is still a mass-produced product that must have a reasonable business case to exist in the GM portfolio. As a result, both Chevrolet and its suppliers (including Brembo) have cost targets to shoot for. However, both companies agree that no compromises will be made to the brake performance to lower cost. The radiated pistons on the Z06 front caliper are a good example of a component that you wouldn’t normally find on a production caliper, but Chevrolet chose to use. For those unfamiliar with radiated pistons, they are made with a fairly complex manufacturing process (expensive) that reduces the thermal conductivity of the pistons, this reducing heat transfer from the friction surface.

The Brembo High Performance Kit (HPK) offerings exist to fill a niche beyond the original equipment hardware. In many cases the HPK systems are larger than stock, offering higher performance and style, but may require the customer to buy new (larger) wheels and tires as well. Many HPK packages offer friction materials that provide higher performance than the stock hardware, but at increased levels of noise/dust/wear than wouldn’t be accepted at an Original Equipment (OE) level. A few HPK packages offer exotic products that would be impractical to produce at an OE level, such as the billet-aluminum nickel-plated “GT-R” calipers. In general, the High Performance Kit product line exists to serve customers that want a higher degree of customization and/or performance, albeit with a few acceptable compromises.

Regarding questions about the brakes or any other part of the vehicle, your Chevrolet dealer is the best authority to answer them. Generally suppliers (like Brembo) are prohibited from providing direct support for Original Equipment products, in order to avoid potential conflicts with Chevrolet Service.
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Old 08-09-2017, 10:39 AM
  #57  
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Default 2015+ water pump housing discontinued, not available anywhere

The answer thread is here.

FYREANT asked:
It appears that the water pump housing for the 2015+ C7 is listed as being discontinued (all part numbers for it) and no dealer in the country is able to get this part. There are members that are looking for this part and have their cars down for service waiting for this part to become available with no known ETA for a fix. Would you be able to shed some light as to why the current part is discontinued without a replacement being immediately available? I am sure that C7's are still being built everyday in Bowling Green, so perhaps the part number got changed and due to a clerical error, nobody knows the new part number? Thanks
Tadge answered:
Thanks for the question, fyreant. I can understand the confusion. We have made part number changes as we continuously improve our production and service parts. Your question asks about 2015 and later cars, but I thought I better talk about 2014’s also. We also have to distinguish between the water pump kit (pump and gasket) and Crossover assembly which includes the water pump and manifold (what I think you are referring to as a housing). For 2015 and later cars the most current part numbers are 12681259 (crossover assy) and 12683013 (pump). The pump and gasket are actually back-serviceable to 2014 model Corvettes as well. Although we may have had part shortages for these part numbers in the past, our system is currently showing availability for both right now. Note also these part number are good for both LT1’s and LT4’s.

For 2014 Corvette owners wanting the full crossover assembly, that part number is 12688645. This part is replacing the previously available 12679050. We have sold out of the old part number, but expect deliveries of the new part number next week. Based on outstanding orders, we will have more than enough stock to cover everyone.
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Old 08-18-2017, 01:28 PM
  #58  
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Default How to Decipher eLSD Display

The original answer is here.

jcthorne asked:
Can you tell us what the information in the eLSD display screen means and how one might make use of it or understand what its trying to tell us.
Tadge answered:
Good question, jcthorne. Many people have asked about that display. Electronic limited slip differentials (eLSD) have only been introduced relatively recently, so many are unfamiliar with the details of their operation. The Corvette is a very sophisticated machine and we try to provide instrumentation that is accurate, readable and informative about the hardware. When we first decided to add eLSD to the 7th generation Corvette, we started thinking about how we would inform drivers about its operation and decided an added display might be interesting to some customers.

Generally speaking, we try to calibrate our chassis controls so that they are virtually invisible to the driver. The idea is to integrate our electronic and mechanical systems to the point where the Corvette just feels like a naturally great handling car - intuitive and benign without unwanted interventions that take the fun out of driving.

Normally I write answers on the forum myself and check in with appropriate experts for additions or suggestions. I can't take any credit this time. Our eLSD integration engineer, Jason Kolk, provided a detailed answer below. He is one of several chassis controls engineers who calibrate the chassis controls to great effect on the Corvette.

Also, I would be remiss if I didn't remind everyone that the eLSD does some of its most important work in some pretty aggressive maneuvers. That is not the time to be looking at the display.... First priority is to keep eyes on the road!

Jason Kolk answered:
eLSD is standard on all Stingray Z51, GrandSport, and Z06 models. The eLSD display (the bottom page in the Performance display group) was added in the 2015 model year to Corvettes equipped with eLSD. There are two pieces of information on the display, eLSD clutch coupling percentage value on top in yellow, and the slip percentage of the rear wheels on the bottom in white shown in the bar graph.

eLSD Percentage in the top/middle:
In the center there is an image of the car, two wheels and the differential. The differential lights up as the eLSD coupling increases. The value shown is a percentage of the full locking coupling capability, and it is the actual value reported by the actuator. When we calibrate eLSD, we work in units of torque. 100% corresponds to 2000 Newton-meters (1475 ft-lbs) of break-away torque (every 1% is 20 Nm (14.75 ft-lbs)). Said another way, while holding one wheel stationary it would take 2000 Nm of torque on the other wheel to make the clutch between the two wheels slip if the display read 100%. For reference a C6 mechanical differential clutch pack was roughly 120 Nm (88 ft-lbs). The actuator is very quick to respond and is able to change from open to locked (0 to 100%) 150 ms (.15 sec) in order to respond to any dynamic situation.

There is a lot going on behind the scenes in the software to come up with the eLSD coupling that you're seeing here. There are a number of algorithms that are running at the same time to collectively decide how much coupling is needed for the different vehicle dynamics situations that they each monitor and control. We have some logic to decide which one of them wins out or which ones add together to deliver the final command that you see on the display and feel in the car.

At the most basic level, the eLSD can have a subtle but profound effect on the handling of the car. We really consider it to be a 'base chassis' component. It's something that plays a big part in setting up the character of the car.
  • Off-throttle, more eLSD coupling adds stability, but too much can be a bad thing. The eLSD is connecting the two wheels so in a turn it's trying to slow down the outside wheel and speed up the inside wheel. In other words the eLSD clutch coupling is trying to oppose the direction that the car is turning, so setting this off-throttle level is pretty important to keeping the car feeling agile. In a steady turn this can help tune the amount of understeer the car has. In highly dynamic maneuvers, this results in something that we call yaw damping where it will reduce the rotation rate of the car.
  • When the driver is on-throttle, the eLSD clutch can shift torque from the inside wheel to the outside wheel. This has the combined effect of minimizing or eliminating inside wheel spin, but it also controls how much it feels like the car turns with the throttle. More torque on the outside and less on the inside will help the car turn - to a point, but that's the balance we're constantly searching for while we tune the software.

Each package is tuned individually so a Z06 won't have the same values as a Stingray Z51, for example. Automatic and Manual transmissions have different calibrations, and even suspension and tire packages like FE3 and FE4, FE6 and FE7 do differ from each other.

eLSD is fully integrated with the stability control and Performance Traction Management (PTM) systems.

Note that changing from Tour to Sport to Track has no effect on eLSD mode. eLSD mode does change automatically when the Traction Control button is pressed. No unique input from the driver is required.
  • eLSD Mode 1 is the standard mode when the vehicle is started. It is optimized for how torque is delivered with Traction Control active and off-power there is an emphasis on vehicle stability. Mode 1 is also used in Performance Traction Management Wet mode.
  • eLSD Mode 2 is engaged when both Traction Control and Electronic Stability Control are turned off. This calibration provides more nimble corner turn-in, and is optimized for traction out of corners.
  • eLSD Mode 3 is engaged when Performance Traction Management is in Dry, Sport 1 & 2, and Race modes. Off power this is a nimble calibration with similar functionality as eLSD Mode 2, however, it is integrated to work with Performance Traction Management when the driver is on power.
  • eLSD Mode 4 is engaged when Traction Control is selected off, but stability control remains on. Vehicle stability is still the priority, while allowing for optimized traction out of corners.
Here are some examples of what you may see if you watch this screen. I'll talk generally, so the numbers may not match exactly what you see, but the trends should be there:
  • Bleed events. The actuator needs to bleed small amounts air out of the hydraulics every few keys cycles to keep things operating consistently. As a driver you may see a couple of spikes to 100% at very low speeds while going straight. This is totally normal and can only happen in a relatively small range of steering on-center so you won't feel it in tight parking lot maneuvers.
  • Driving straight down the road, we have some speed based preload to add stability and on-center feel. This is going to be relatively small and you will only see a small amount around 10-15% at highway speeds. You'll notice that when you do steering inputs and simple lane changes that it drops down slightly and then pops back up when you are going straight again. This strategy is to improve steering feel and agility. We can be more open at low speeds than previous fixed clutch packs (C6 was fixed at 120 Nm (88 ft-lbs)), and then add more at very high speeds to add stability.
  • On larger throttle applies you will see eLSD clutch torque grow, and these could be the largest amounts of eLSD coupling that you'll see under normal circumstances. On track this could go as high as 40-50%. The goal of this algorithm is to maximize rear traction while cornering and tune the feel of how much the car is turning while you're on power.
  • The largest eLSD coupling will happen under very extreme lane changes and slaloms where we can nearly lock the eLSD clutch to add stability at just the right moments, but open back up to allow the car to steer through double lane changes at just the right times.
  • If you were to drive your car in the winter and start with one wheel on ice and the other on bare pavement, you may see clutch torque build in response the wheel on ice slipping to keep it under control and to maintain smooth acceleration.

Wheel Slip percentage on the bottom of the display:
The important thing to know here is that this slip display is not directly connected to the eLSD software. This wheel slip display has its own calculation and it's showing the average rear wheel slip compared to the average front wheel slip. It's not showing how much slip is occurring across the eLSD clutch (between the two rear wheels), even though I can see how a driver could make that connection. ` Think about this as showing how much rear wheel spin you're getting at the drag strip in a burn-out box, for example.

There may be rare instances where you see this display flicker when you first start to move or when you come to a stop. Don't be alarmed by that, it's function of the math behind the display when the numbers get really small.
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Old 08-31-2017, 12:42 PM
  #59  
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Default Indexing Spark Plugs

The answer thread is here.

grcor asked:
Every year or so the topic of indexing spark plugs comes up on the Forum. Some say don’t bother as it makes no difference at all, others say it will add a couple of horsepower and to position the spark plug gap towards the intake valve or position the spark plug gap towards the exhaust valve. I know that when you are designing a new engine a lot of super computer time is dedicated to combustion chamber design and spark plug placement. Could you please ask the engineers who are involved in combustion chamber design if they would comment on indexing spark plugs? We would like to know if it makes a difference, if so how much of difference (a few, 5, 10 horsepower?), and what is the correct orientation of the spark plug in the combustion chamber. If possible a picture or drawing showing the correct orientation of spark plug in the combustion chamber would go a long way to eliminate any confusion coming from a written description.
Tadge answered:
This is not a Corvette specific question, but I did exactly what you asked and consulted the experts on combustion optimization. Here's what they had to say:

Indexing the spark plug has been a topic of discussion for decades now. Theoretically, you would think that the spark plug position would have some impact on combustion and performance, and it may have had an affect years ago on poorly developed combustion systems and low energy ignition systems. However on modern engines, like the Small Block Corvette engines, significant engineering work is done to develop the combustion system. We use Computational Fluids Dynamics, Combustion Performance Analysis, Single Cylinder Engine combustion development, and engine testing to optimize combustion performance. This significantly decreases the benefit, if any, of indexing a spark plug in the chamber. In effect the combustion system's design ensures thorough mixing of the air and the fuel in the chamber rendering indexing to be of little benefit. Since the plug initiates flame propagation from near the center of the chamber and all other parameters are optimized around that location, complete combustion of all the air and fuel occurs in the minimum amount of time. Once you have achieved that, there are no more benefits to be gained through other design or geometric changes.
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Old 09-14-2017, 11:15 AM
  #60  
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Default Corvette Seat Care

The answer thread is here.

Maxie2U asked:
There is much debate among C7 owners whether the seats in addition to periodic cleaning need to have leather conditioners applied periodically to the leather portions of the seats and vinyl conditioners applied to the "leatherette" portions. Many owners say the seats have a protective coating so the seats only need to be cleaned occasionally but not treated with conditioners because these treatments will damage the protective coating.

What is the real story on interior care?
Tadge answered:
Corvette, like all GM products uses interior materials that are extensively engineered to meet some very tough requirements. Seats in particular need to be resistant to abrasion, wear, ultra-violet radiation, intense thermal cycling (it can approach 200 degrees inside the car when parked in the sun in the Arizona desert or Mid-East. We also have to consider the Canadian or Norwegian customer who's car may experience 40 degrees below zero) in addition to soiling and stain resistance. The materials we use are treated and coated to meet these requirements. Aggressive cleaners will make the car look better in the short term, but can damage the protections, so it will be more susceptible to wear and soiling over the long term.

Our recommendations are the same for leather and other leather-like materials. If at all possible, do the cleaning with a damp micro-fiber cloth. If that doesn't work, add a little of the mildest soap you can find. Do not use products like Fantastik, liquid detergents, or bar soap. GM offers a leather, vinyl and plastic cleaner (Part number 88861401) that has been validated to be compatible with our interior materials. Any car that is used regularly is going to get dirty. Staying ahead of it and avoiding build-up is the best strategy. If you clean more often, it is more likely that the least aggressive technique will work. Think about using the damp micro-fiber cloth on the interior every time you wash your car.

One final point: There are numerous companies that provide professional cleaning services for vehicle interiors. We can not make any specific recommendations here other than our cumulative customer feedback is mixed at best. We have seen many cases where customers' cars have been permanently damaged by caustic chemicals and aggressive cleaning methods. If you want to use one of these services, make sure you talk to previous customers and look at their cars after multiple times through the process.
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