by capev86 » Wed Sep 24, 2008 4:26 pm
if you have a naturally apsirate 2.2 or 2.5 - don't go over 2" diameter pipe - you will sacrifice low end response and torque for the sake of high end breathing. better idea is to replace the stock catalytic converter with a high flow unit and get a low restriction muffler. these engines like efficiency of flow over volume of flow - you want to keep exhaust gas velocity high.
on a mitsu turbo equipped car - 2.5" exhaust all the way. the downpipe is 2.5" as of 1989 but the rest of the exhaust is smaller and restrictive. go to fwdperformance.com and get a 2.5 inch mandrel bent system (available in stainless steel too). the kit for a spirit is correct for atleast a 4 door/wagon k car. consult them for other applications
if you have garret turbo (especially intercooled applications) the ultimate setup is a 3" fwdperformance.com system with a 3 inch swingvalve from turbosunleashed.com. the bigger swingvalve will give you 5 more hp and 30 more ft-lbs of torque over a factory 2.5" swing valve. its pricy at $250 but worth the added power with no compromises relief it brings!