Originally Posted by Asahi
Based on your other parts 2.25" is fine. But 2.5" is proving to be the real power maker. You should consider a 2.5" collector header and 2.5" exhaust (Custom since 63mm is the largest brand name size I know of before 3").
A test pipe won't make more than 1 to maybe and it's a big maybe 2 hp over a high flow cat. If any power at all. the cost is the true justification.
The only thing that I'll be upgrading my header with at this point is a turbo manifold and downpipe
. I like my Comptech stuff, and as proved by the "Great Header Test" it performs just as well as anything with a bigger collector. So based on my situation, where my only modifcations are bolt-ons, I feel like my bottleneck is the cat. I'm not going to be replacing either the header or the exhaust so I thought that a test pipe would be a good next step. Don't get me wrong I'd love to upgrade those parts, but it's not something that is feasable at this point. With cost indeed being the true justification it's looking like it will be cheaper to go with a test pipe and o2 simulator than to buy a CarSound High Flow cat.