I've seen a couple of GT races with Porsches, Ferraris and the like. I've always wondered about 2 things.

1. Is EVERY aspect of the cars performance upgraded? (Transmission, suspension, engine, motor)

2. How are the manufacturers responsible for the car's performance? If most of the car is upgraded, then that means the manufacturer doesn't deserve the award for the car winning, instead the company that modded it should get the award.

Help would be appreciated.

GT cars (well some classes, anyways) have a rule that all specification must stay the same; ie you porsche MUST stay rear engined, rear drive (GT3), must use a tuned flat 6, etc. This brings out the strenghts and weaknesses of each car, meaning the viper still owns the straights, but still gets pwned by the porsches in the corners, the vettes are OK everywhere, the Lamborghini still spontaniously combusts, etc.

1 - the cars are re-built from the ground up, using all new technology, i'm not sure on the chassis ruling, but I thikn most of them are rebuilt with CF chassis rather than the standard chassis.

The Engine must remain the same as in the road car, although modifications are allowed to it.

2 - Alot of teams who tune the cars are factory based or sponsored, sometimes, like 911's are available from Porsche direct as well as making them yourself.

GT cars (well some classes, anyways) have a rule that all specification must stay the same; ie you porsche MUST stay rear engined, rear drive (GT3), must use a tuned flat 6, etc. This brings out the strenghts and weaknesses of each car, meaning the viper still owns the straights, but still gets pwned by the porsches in the corners, the vettes are OK everywhere, the Lamborghini still spontaniously combusts, etc.
Vipers have massive tires, I think they could still corner pretty good.