I have a s-5 n/a motor, and i currently am running a header back to flex pipe back to the y to some hollow cans. around 2.25 inch except for the stock y pipe.

I picked up a high flow cat to shut my car the hell up. and the only problem is its 3 friggin inches inlet and outlet. will that cause a major issue to use with my set-up, I understand that changing id size on an exhaust system is a big deal, but givin this is a cat which impedes airflow, may the extra size actually be a good thing?

opinions?

 

A rapid change in diameter causes some loss. If the smaller pipe size is large enough (probably is) then the exhaust velocity will be low and it shouldn't be a problem. In fact, it is very difficult to screw up on the piping. Large pipe and smooth bends are just hype. It is neither hard nor expensive for the OEM maker to make the pipe plenty large enough. And if the pipe is big there's little need for smooth bends. What is difficult to design, without losing power, is noise control and the cat.

 

Probably shouldn't mess you up TOOOO terribly bad, but why are you putting a cat back in?

 

oh, nvm. i can't read. What mufflers are you using? and how old are they?

 

they are some kind of knock off hks or greddy style cans. they look good and sound good, but when you hit a hill all bets are off, it sounds like im drag racing the van beside me at 25% throttle.
plus hopefully this will give me enough backpressure to open the 5/6 ports i plan to reinstall.
and im pretty sick of looking shady hanging outside of inspection stations with a $20 for a inspection sticker.

pic of the cans

back when she was still in s4 trim