spdkills

I was thinkin bout gettin the Perrin Down Pipe w/o cat and a perrin up pipe w/o cat but then this would make me emissons illegal? Then I started to think bout the stromung down pipe with the high flow cat and the 3rd cat remover while still getting the perrin up pipe? How much would the 1/2 in pipe size hurt performance? Also I have a 3 inch greddy evo cat back.

Thanks for the help.

wrxboxer4

I would say it depends on what your HP goals are. Depending on whether you want to eventually get 400HP or is 300HP enough. If you plan on changing the turbo or not. If your not planning on a turbo swap then the 2.5in downpipe is good enough. It will give you better low end torque than a 3in. Like I said it depends on your goals.

GLwagon

I have heard that unless you have a rigerous visual inspection the 3rd cat alone will make it.

BUT, all of the Perrin down pipes replace the down pipe & 3rd cat... If you buy the version with cat it should make emmisions with minimal hp loss...

If you live in an area that has any kind of emmisions insp. you will need a cat some where in the system...

Bosal, Scooby Sport & some others are direct dp replacements that keep the factory 3rd cat.
I would recomend a bellmouth or twin dump design VS. the factory & old Stromung dp designs with the flat plate over the waste gate.
If you don't care some go totaly catless

As far as 2.5" - 3"
If you want torqure, plan on keeping the factory turbo 2.5 is perfect...
If you want top end & have plans to upgrade a lot of things inc. Turbo you'll want to start on a 3" system

I belive at this point Perrin is the ONLY mfg. with a true 3" down pipe... I havent looked at the systems that are "turbo back" someone else may have one.