So i was just curious if the B5 Ko4 is needing back pressure to run right or can you just throw on stright pipes all the way back? I am about to take it to the track for the first time so i was just wondering if it would make any difference? How much if so either way good or bad. i know it wont pass emissions with stright pipes but i could just make a swap out 1 piece pipe if it works. any info?

 

As far as performance goes a straight 4" pipe would be great but its loooud. Id reccomend electric exhaust dumps before or after the cats that way you can be free flowing and loud when you want, and toned back for daily use.

 

yeah think of back pressure for a turbo like trying to stop a fan from moving the way it wants and turning it the other way. This is why turbos have wastegates so when the back pressure builds up it dumps to the air(that brass round looking thing on the turbo is the wastegate). So on turbo cars like hp said you can run as big as you want.

 

Wastegates are used to controll boost by working on the exhaust gas side(turbine side) of the turbo. They let some exhaust gasses bypass the turbo so it dosnt keep spooling and making boost. There is no mechanism for dealing with or adapting to back pressure other than exhaust modifications

"Compressor surge" happens on the compressor side of the turbo because the blades are still trying to force intake air into the engine while the throttle is shut. Here you use a BOV/DV to divert the air and prevent shock to the turbo. This dosnt happen on the turbine side, it would be analogous to sealing off your exhaust. Exhaust side its more like a windmill (its being pushed by exhaust gas) compresor side is like a fan (driven by a shaft and pushing air)

A more freefowing exhaust will give you better throttle response, faster turbo spool, and more power (all do to less backpressure and greater flow). You will notice the difference and probably love the sound. Also it dosnt have to be illegal, a nice set of downpipes (AWE, ASP, Labree, APR, Miltek) combined with some electric exhaust dumps and an aftermarket or custom cat back (i like dual 2.25 or 2.5) will give you just about all the performance and sound you could want and you might have a chance at passing emissions depending what state your in...