Thats all a moot point, McLaren denied his warranty claim without following the law. Straight from the Federal Trade Commission website:You have no idea. For example, how do the modifications affect the resonant frequency of the exhaust? How does this interact with the waste-gate control algorithm?
As for lowering the car, the suspension geometry is optimised around its normal equilibrium position. Changing that risks premature wear and invalidates some of the active suspension's design parameters. I would be suspicious that the previous issue wasn't fully fixed, so wouldn't have risked a mod.
Modern Engineering is complicated. You cannot trust your gut feeling on how modifications will affect the complete system.
1. "Simply using an aftermarket or recycled part does not void your warranty."
2. "Magnuson-Moss Warranty Act makes it illegal for companies to void your warranty or deny coverage under the warranty simply because you used an aftermarket or recycled part."
3. "The FTC says the manufacturer or dealer must show that the aftermarket or recycled part caused the need for repairs before denying warranty coverage."
OP says "McLaren denied my warranty claim because my car has a catless exhaust system and said that it voided my engine warranty." Which is illegal. McLaren needs to do more than that before they can legally deny his warranty claim. You people need to learn your rights and realize that sucking McLaren's cock won't get you anything.
OP, they already have bulletins for the issue published? Get that and give it to your attorney, go sue them. You may have a case.