What was done to the Champion RS4 Race Car to get 500HP. I know it had a stock aribox and straight
 

pipes but what else?? I am thinking about having a valve connected to the sport button so i can either drive with the stock exhaust or straight pipes, what do you think?

I believe that car had custom headers and engine tuning

probably no cats and tuning for race gas.

You're both right, scroll down to details about the RS4 challenge car.
 

<ul><li><a href="https://www.audiworld.com/news/07/alms-vitesse-rs4/content.shtml">https://www.audiworld.com/news/07/alms-vitesse-rs4/content.shtml</a</li></ul>