My buddy has a 01 eclipse GT with k&N typhoon intake, centerforce dual fricton clutch. Recentley he had a exhuast system
put on. He had them cut my cat and run 2 1/2 from the collecter
back out to a dnx muffler. Since then his car is slower. At the track his car runs 3 mph slower than it use to. So what did he do wrong? Does he need to get a adjustable fuel regulator or does he have too much flow. I know it had 3 cats, I know he's got some kind of back pressure right?

 

he probably lost way too much back pressure and is causing him to run slower

 

does he need to put a stock cat back on there or get a high flow cat