02-07 Subaru WRX & STI Downpipes
02-05 WRX NOTES: The 02-05 2.0L WRX has no boost spike or creep issues related to catless downpipes.
06-07 WRX NOTES: The 06-07 WRX has boost spike or creep issues in all cases with the use of a catless downpipe because the 2.5L engine pushes so much air. Even with the internal wastegate fully open, not enough air can exit to stop spinning the turbo, resulting in boost spiking. This problem cannot be fixed with wastegate porting alone; we suggest wastegate porting and engine management to remedy the situation. Due to this, 06-07 WRX owners may want to consider waiting to get an aftermarket downpipe or turboback until after they have upgraded their turbo or they may want to consider getting a cat-back exhaust only.
04-06 STI NOTES: The 04-06 STI has boost spike/creep issues in all cases with the use of an aftermarket downpipe or turboback that uses a bellmouth or external dump tube design. Even with the stock internal wastegate fully open, not enough air can exit to stop spinning the turbo due to the flow of the 2.5L engine, resulting in boost creep / spiking. You can fix the problem by porting the stock turbo's wastegate passage (any exhaust shop should be able to do this or it can be done at home if you know what you're doing) or you can get an engine management system to fix the issue, like a UTEC or AccessPORT.