MustangsEatSi

so i just installed 2.5 flowmaster american thinder on my car with a catless H pipe, and now it backfires in upper RPM, and has no pull in upper RPM either. It is a stock motor with a lumpy cam and GT40 upper/lower intake. Tommorw I am gonna put the stock H pipe back on, can anyone tell me if this is the best idea? thanks

roundman

changing the H-pipe should not have caused this. try resetting the computer by removing the negative battery cable for a few minutes and then reconnect it and drive the car and see if it still does it.

jeep45238

Re-set computer.....then be a man and get an X pipe.

Anyone saying it'll make your car sound like an import is *jacko voice from southpark* just ignorant *jack voice off*. I'd actually pay to find someone be able to take a modern day "big displacement" V8 sound like a nasty *** 4 banger.

gmkilla

Make sure there are no exhaust leaks...sounds like I have a similar setup to you, and after installing an h-pipe w/no cats I had a small leak between my header and h-pipe, and the thing would back fire every time i let off at higher rpm's. Fixed the leak and it was gone.

VertStangGT86

When you're looking for the leaks check for soot marks around the joints. Or spray some soapy water on the joints then start it up and look for bubbles.