I'm planning on getting around 300-350 whp at 15-17 psi. What size of exaust should i go for? I now have a 2,25 inch exaust, is this good inough. Or do i realy need a 3inch exaust

 

What engine are you running? 3 inch would be ideal, however, it would also better if you can match the exhaust with a 3 inch downpipe and cat/testpipe.

If you search around you can probably find some people running 3 inches as well as 2.5 and you compare their results. I pretty sure there are some dyno charts floating around as well.

 

I was gonna do a custom setup for mine, then i decided the Thermal would be the best choise for myself. So I say Thermal 3"

 

Ideal would be 3" downpipe, 3" cat or straight pipe, 3" exhaust. That would yield you the most power and quicker spool time.

From my experience and reading its best to get the same exact size all the way from downpipe/cat/exhaust. But thats just from opinions, etc. The bigger the better if your making good power

 

If you can weld or have somebody weld it for you go with http://www.kteller.com and get 3 inch exhaust from your turbo to tail pipe.