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| JSC Speed: WRX/STi Exhaust 101 |
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OVERVIEW:
Manifold & Uppipe -
Downpipe -
Cat-Back Exhaust - Turboback Exhaust -
Rear Muffler
Replacing the exhaust system on your 02-07 WRX or 04-07 STi is a great way to increase power. Unfortunately, there is a lot of misinformation out there, and the exhaust system is composed of many different components, making it difficult to fully comprehend. JSC speed has developed this informative guide, titled 'Exhaust 101' as a means of providing correct information and simplifying WRX & STi exhausts using visuals and summarized information.
NOTES ON CATLESS DOWNPIPES BY MODEL:
02-05 WRX OWNERS READ: On the 02-05 WRX there are no boost spike or creep issues in most cases with the use of an aftermarket downpipe or turboback.
06-07 WRX OWNERS READ: On the 06-07 WRX there are boost spike or creep issues in all cases with the use of an aftermarket downpipe or turboback. This is 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, the result is boost creep or boost spike. With the 06-07 WRX, unlike the STi, you cannot fix the problem by just porting the stock turbo wastegate, since the problem has to do with the actual size of the turbo. We suggest porting the stock turbo wastegate AND getting an engine management system to help fix the issue like a UTEC or AccessPORT. With the added costs this will entail, 06-07 WRX owners may want to consider waiting to get an aftermarket downpipe or turboback after they have upgraded there turbochargers or they may want to consider getting a cat-back exhaust only.
04-06 STi OWNERS READ: On the 04-06 STi there are boost spike or creep issues in all cases with the use of an aftermarket downpipe or turboback that uses a bellmouth or external dump tube design. This is 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, the result is boost creep or boost spike. 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) or you can get an engine management system to fix the issue, like a UTEC or AccessPORT. The upshot is that you will also pick up some more power with engine management.
2007 STi OWNERS READ: The improved turbocharger design on the 2007 STi eliminates boost creep with aftermarket downpipes.
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