I would suggest staying with the stock headers, and spend your money on a real 3" down pipe that clears ATR headers. The Kirban down pipe is a "slight" improvement over stock, but the stock elbow is the real restriction. Buy the headers if they are reasonable in price, and use them when you approach the 650+ hp mark. THEN they will be a gain, but NOT until then. I have built cars that run 11's with a stock down pipes, but a well built 3" pipe would have gained the cars a few tenths/mph. Good luck.:smile: