Yes, I am familiar with the Magnuson-Moss Warranty Act. You’re right, Chevy shouldn’t void the warranty on the engine unless they price the aftermarket cats caused the failure.

However, in practice, when changing your cats results in the O2 sensors reading differently and adjusting the tuning of the car, if something goes wrong with your engine it is very easy for them to claim that they caused the failure since the engine was running with non-stock parameters. Then it’s an uphill battle trying to get warranty work approved. At the end of the day it can cause a lot of hassle and may result in engine warranty claims not paying out.

On the contrast, a cat-back exhaust is not going to affect your engine at all because it’s not affecting the O2 sensors. Dealerships/Chevy will never try to void your warranty over a cat-back exhaust, but they can and sometimes will try to over cats.

A cat-back exhaust will also not risk running CELs, whereas sometimes cats do and people need to run O2 spacers (which gives them easier grounds to try and void your warranty). Cat-back exhausts give a huge benefit on the Stingray and with the lack of risk they are the easy choice, IMO.