I know that they make 2 1/2" and 3" high flow cats. I just bought a apexi N1 cat back and i don't know the sizing on it. Does it matter what high flow cat i should get? Please let me know what you think. Also, how hard is the intall of the high flow cat? -thanks

 

I'm almost certain your catback is 2.25", and yes they do make hi-flo cats with a 2.25" collector.

Shingo

 

If you put a piece of 3" tubing onto a piece of 2.5" tubing, you will get turbulent flow, which is bad and will create backpressur you are trying to avoid, and probably sound funny.

 

Another thing is what header do you have???? That plays a part in what size hi flow cat you can get...

 

right now i don't have a header. i am saving for the b18c5 swap.:naughty: I will eventually go with the dc header. thanks for the responses