For those of you wondering about previous issues with AFM valves and changes for the 2017 Corvette, the following is from Corvette Chief Engineer, Tadge Juechter:
Tadge Juechter said:Corvettes have long pushed the technology envelope to make a car that is both supremely fast and remarkably efficient. That often means we are doing things no other manufacturer would try. The combination of true cylinder de-activation (meaning keeping cylinder valves closed, not just turning off fuel injectors as many others do) in a track-ready car is an example. We did do our normal 24 track testing with the AFM valves in place without issue. Perhaps the way we run our test can help folks running on the track avoid problems.
A few important points: The valves are very sensitive to air flow under the car. Anything that restricts that airflow could increase the chance of an issue arising. These would include any aftermarket aerodynamic or cooling aides. Also, lowering the standing height (which many folks are tempted to do to lower the center of gravity) of the vehicle below spec has a measurable negative effect. We always run at least one complete cool-down lap before pitting. This is super-important because the relatively cool exhaust gases running at part throttle cool the AFM valve quickly. Finally, some tracks have noise regulations that cause people to run in stealth mode. That is a relatively recent trend, so we did not validate track durability in stealth mode. It was always intended to be a street feature.
The question cites the “plastic” actuator with the implication that we used non-robust materials in such a hot area. Although the accompanying photos show thermal distress in the glass-filled nylon case, that is an effect of the internal thermal failure , not the cause of it. Actually the internal magnets and electronics are the thermal weak link and there is no material substitution in the world that can be used to fix it.
So what can we do about it? For the 2015 model year we added insulating content into the muffler head to reduce the thermal load on the valve. That was a continuous improvement, but not a “clean kill” for every situation. For 2017, we have eliminated the valve on Z51 and Grand Sport (manual transmissions only). Manuals still have AFM, but the torque levels are low relative to the automatic so the N&V issues are manageable without it. Also, the AFM only works in Eco mode, so it is easy to avoid if you want to. The 2017 manual transmission hardware set is not an easy “bolt in” for prior year cars, so we are studying how to make that solution available. The automatic is likely to need the AFM valve for the foreseeable future. The great thing about this “Ask Tadge” activity is that it lets us hear very directly from customers. We will ramp up our efforts both in our mainstream engineering and our performance parts activity to see if we can have better solutions available in the future.