z51rox

Yes I do...When the car is in Sport :wet, dry and sp1 and sp2 the car is applying abs in various degrees on entry and exit which in turn heats up the brakes. The eLSD is also apply varying degrees of torque/clutch engagement which again translates into heat. All of this heat that is being generated now flows through the entire driveline. Which cause all types of issues with the car on the track. That is why on a real race car there are ducts and louvers all over the place to rid the chassis of heat. When in "Race" mode most all of these nannies are turned off and a lot less heat is being generated throughout the drivetrain and chassis. This is my own opinion after numerous times on the track experimenting with all of the PTM settings. When left in Race the car never once heated up oil,water,etc. Brakes no fade even when late trail braking on entry.

OldJedi

Would you mind explaining what you did for a transmission cooler and is it working to keep it cool? Front or rear mounted?

Theta

I'll give you that - you're right on all accounts there.

From the perspective of the AFM valves, though, it's a matter of EGT and radiant temp in that immediate area. The design issues come more into play with them being at a rising high point, not being de-coupled, etc.

I do appreciate you expanding on your comment, though - too often we have posters here who will throw something out on a whim without any reasoning behind it. In this case, you're making a good point about the increase in heat/wear on the e-LSD, transmission, and brakes.

That being said, there have been [large amounts] of AFM actuator failures on track cars in full race mode (7-second hold, all assists off) from newly gathered information.

Personally speaking, as someone who generally races in Sport 1 or 2 due to the overwhelming power level of the car, I worry about the amount of wear and stress being placed on the e-LSD, but that's for another thread.

Greg00Coupe

Man you guys are into the technical aspects of these cars.........my hat if off to you all!!!

sxeC7

Am I correct in assuming that the only reason for the AFM valve is to change the exhaust sound when in 4 cylinder mode? If so, it would be simpler to use something like BMW's exhaust sound replicating system over the stereo to do it, IMHO.

FYREANT

It also controls the amount of back pressure in the exhaust which is important.

Theta

Beat me to it! To answer the previous question, though, this is to a lesser degree, and essentially regulates the 'irregular' pulses that essentially make the car sound like it's missing. I'm unsure of how fast the valves are moving, but at maximum speed, the actuators would not be able to match the speed of the exhaust pulses, so they generally just hold a specific angle while DoD/AFM (V4) is engaged.

They wanted to make it sound better on the outside, because it doesn't sound very good to onlookers in V4 mode. A bit silly, since the Z06 doesn't worry about this. For that car, they chose function over form, and I applaud that decision.

Having driven over here in my M with the ActiveSound 'fake' engine noise, I have to cringe at the suggestion. I'm totally fine with that if they would allow the user to turn it off. We can change/remove it on the BMW through coding, but I've been too busy to mess with it. Once move 6cyl performance cars hit the market, I'd expect this to become less unusual.

baron95

Just to let everyone know, my 2015 Z51 A8 also just had this fault. Car sounds horrible just idling and between 1,000-1,500RPM has this incredibly loud, continuous, metal banging noise coming from the exhaust. It is embarrassing.

Not only the C7 is the only car on track that overheats the tranny after 10-12 minutes on track (even at 39F/3C temperatures, and minimizing shifting), now it seems like my exhaust has self destructed.

Here are the codes that my car there:

P12F0 cylinder deactivation exhaust flow valve stuck open (seems to be the problem)

P26C8 chassis control module requested MIL illumination

Car is parked, while I wait for parts to arrive at the dealer (they said about 5 days to get them).

This notion that it is only one or two cars that this is happening to is absurd. If you drive the car hard, it overheats the transmission and apparently the entire rear transaxle area.

Even the instructors at Spring Mountain make you up-shift the automatic C7s at 4,500RPM in their Mickey Mouse track to prevent overheating.

So, to answer your question, I think the difference is actually driving the car hard. Do it, and it overheats and starts to get all sorts of failures. I am an HPDE instructor and occasional racer, and I have driven and instructed in every imaginable car. The C7 Corvette A8 has the worst thermal envelope of any car I've ever been in on a track. Period.

baron95

Just to let you know, my car does not have MagRide/PTM and I drive it on track exclusively in Track mode with traction control and stability control fully off, and my AFM is toast and dealer is waiting for parts to replace it. It failed in a 60C cloudy day, while I was simply playing on an autocross track for 5-7 minutes at a time with no significant braking and the whole time in an easy 2nd gear.

What ever it is that destroys the AFM is not related to PTM/traction control or rear brake overheating or high ambient temperatures or frequent shifting.

The car simply does not have the thermal envelope needed to even do 10 minutes on track if pushed.

leadville1

I run mine all the time at the track and have never had this issue but I have my pipes wrapped with DEI from the transmission back to the exhaust. I had one weekend where I put on 1000 miles on the track and never has any problems. I also use the Z06 ducts in the rear fenders.

Jack Be Quick Racing

okay, so what does Spring Mountain and others do to their fleet of 2014 and 2015 manual and auto Z51's that is different than this? Not every participant is doing parade laps during those schools especially in the level II courses.

Given the AZ and Las Vegas temps, 20 minute lapping sessions, ongoing use of the cars.... wouldn't the AFM failures been everywhere already? I didnt see it but some reported engine overheats on here, didn't they?

I know the first response will be something like they aren't pushed as hard as other track cars but, I find that hard to believe in all cases and the repeated, dedicated track time of the cars certainly is going to be more stressful in heat cycles and repeated use then a part time tracked street driven C7.

I would think it would be extremely visible in these track school environments.

baron95

I am told that on the A8 cars they make you up-shift at 4,500RPM.

I was signed up for Level 2 in October, but had to cancel due to work. I'm now doing it in December. I'll let you know how it is run.

In my experience drivers with less than several track days under their belt rarely of full throttle on track. Good advanced drivers, will go full throttle and stay full throttle whenever possible, and will do all they can to spend as much time as possible at full throttle. That is a big difference for a car with poor cooling.

Jack Be Quick Racing

well, yes, when I was there I saw several who were not using the car to it's potential. However, the 'fast' students are sectioned off and they run as hard as their skill and instructors take them. There were SCCA licensed drivers in my group who did have a good amount of track time. When we were sectioned off and our laps were quick.

Nothing beats direct experience, however, so I am very interested in following the thread to see where it goes.

descartesfool

The operations manager of the Spring Mountain school e-mailed me that they have AFM actuator failures when I asked him back in 2014 about what issues they were having with the cars relative to issues I was having. He told me the students do not overheat the cars as they drive slow, but that their instructors overheat the cars when they drive quick. He also said that cars were less prone to overheating when 2nd gear was not used. He told me related to their AFM actuator failures that GM knows about it. And just like my Z51, their manual transmissions overheat (300F +) as well when driven hard by instructors.


So you just have to ignore almost anything related to students driving the cars there as it relates to them not overheating any system on the car. Drive the car hard and fast lap after lap and the cooling is insufficient. My GM Customer care reps know about it, the GM Camaro and Corvette Brand Quality Manager knows about it, and the main contact at GM Jeff Strausser who deals with these issues knows about it, and they have absolutely zero solutions to offer for any aspect relating to overheating except to offer me a buyback. No technical solutions of any kind being offered. I just asked again last week to see if they have any solution, and I will be checking at the GM booth at the SEMA show this November.


It is not like some people think that some cars overheat and some don't and that there might be something different about the cars. It is all about the driver and their skill at keeping the car lapping close to the car's potential best lap times. The vast majority of drivers on track do not drive the car near the car's full potential, they don't run consistent lap times and that is why they don't overheat.

StingerBG

Sad thing is, they probably COULD fix the issue, with an exhaust option without AFM and a factory tune to accompany it, basically just make the car a little more simple. Only thing is, if they offered this to you or anybody else who has overheated and melted the AFM actuators (as a recall), then they would have to offer it to everybody that owns a C7 with AFM. And as of now, there are WAY more people not having this problem due to the fact that they don't drive the car hard enough, than there are people like yourself. Therefore, the cost to fix the few would far outweigh the oversight of the problem at hand and just work to fix this problem on future models. Is it bullcrap...YES! If they advertise a product as such, it should be capable of said advertisement. However, they know that most people buying this car will never push it hard enough therefore they aren't worried about really fixing it. Best bet is to say screw the warranty and move on to aftermarket set ups if and when they are available. I know LG has come out with quite a few cooling advancements...whether they are a complete solution or not is yet to be determined. I hate this problem as much as you, but it is simply the way the market works when it comes to mass production and larger companies. They would rather keep production costs down and keep pumping out product to the masses and just accept that they will lose a few customers to other brands due to such failures. That is really a problem caused by making a "race ready" product that is affordable to a larger population. Supply and demand...the devil of quality standards....IMO! (Just food for thought)

descartesfool

I think you are correct on all aspects there. That is what I have come to think about GM. Only point you make I am not sure about is to start modifying the car and forgoing the warranty. If I have had a failure each day I have taken the car to the track, and due to the failure I have limited how many days I have taken the car to the track and limited the total number of laps I have done, how reliable would the car be if I did 10-12 full days per season with 6 to 7sessions of 30 minutes each per day. Not confident car would be reliable at this point due to its current issues I have seen. What else did GM leave out of the engineering design other than cooling? Would adding cooling be enough, or would other stuff break over time with heavy track usage. I have a GT-R which I have been beating on track for 7 years and nothing has ever broken and thus I never used the warranty. That GT-R is dead reliable (with an added tranny cooler). Would my Z51 be as reliable with the same usage? Or should I just move on and get a different brand, AMG GT-S, new Acura NSX, or something else? I want to like my first ever Corvette, but I didn't buy it to wax it.

SBC_and_a_stick

Honestly, it is easy. GM can use an improved set of AFM valves in all cars upon developing one. A new OEM number would be assigned. Some can choose to purchase the improved model from the dealer and get it installed. There is no need to recall a vehicle to improve a part.

Whenver they have a bash or autoshow they can just announce some key parts that were updated. Not rocket science, and everyone would be happier.

StingerBG

I agree with you 100%! But I guess that's why the Corvette is still available for a fraction of the price of all the other cars you listed! With cut costs comes cut standards. I still enjoy driving my Vette, and for me it will subside...however if I wanted to track a car and do so constantly, I believe I would have to spend a little more and get a more track-ready vehicle.

Chets LS3

What takes place when adding an aftermarket exhaust that does not use afm. What has to take place with the afm valves?

Also DF when you have the afm failure is it just a cel? Or does the car go into limp mode. Aka can you still continue your track weekend?

johnglenntwo

8250 RPM Flat crank, and fiber wheels; was thinking about this yesterday