[Guess]

It was a 5.0 Mustang, supercharged

I have never removed plates while tracking my cars, why? Because nowhere in the warranty does it state that a vehicle may not be driven fast in a straight line. I have had Mazda try to deny warranty on that basis on my tranny a while back, and got nowhere with it really fast.

A dealer will only deny your warranty claim if they are out to get you or if your gullable enough to believe that they can. BMWNA would not post 1/4 mile and 0-60 times on their website if they didnt want their cars tracked. Their cars are very performance oriented, and they know they attracked enthusiasts of this nature.