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stock wrx exhaust vs sti

25K views 32 replies 15 participants last post by  mosc 
#1 ·
Sorry to bother but what is difference between stock wrx exhaust system and the sti one?
 
#3 ·
Actually not much difference. The downpipe is the same. It doesn't change until the axel back portion. The downpipe has two cats and is 2.5 inch diameter. The axel back on the STI is still 2.5 inch with a nice sounding muffler. The WRX goes to a 2.25 inch diameter with a really quiet muffler. So if you want to switch to the STI exhuast just get the axel back portion but even then you are only gaining .25 inch in diameter.
 
#5 ·
the axelback itself will yield 0 performance difference, just a different tone. the sti one has an extra resonator in the muffler which coincidently reduces hp gains by a very small margin. and considering the axelback only gives marginal gains, it makes no difference.
 
#15 ·
You should look into replacing the Up and Down pipes. The up has a cat that you dont really need. This is different starting in 06. The 06-07 Up pipe does not have a cat. If you replace the Down pipe, you will notice a big difference. Here, you can go catted, or catless, but the catless is usually considered "race only" and illegal for street use in many states. The STi axle back is basically just going to give you a sound and a different tip. You wont notice that much difference between the STi vs. the WRX axle back power wise. The bottle neck is the Up and more importantly the Down pipe.

WTF?

intake = no restriction Should be good up to several hundred HP before you need to do any significant modification to the intake, You would need to look into this when you are looking at a new turbo, etc.
Catback = no restriction None that is noticable
Up pipe = no restriction This is where I have read different. I have read that the Up will give you quicker spool times, and thusly get you into the power band more quickly. Please correct me if I am wrong.
downpipe = huge restriction YES!!!
(02-07 WRX/STi)

It's that simple. The downpipe is a major restriction. Just switching that out and NOTHING else gives noticeable gains. The rest of it does virtually nothing.
 
#16 ·
the dyno charts I've seen always show little to no gain. The ones that I've seen that show gain are often in conjunction with tuning which is misleading. They remove the cat and then raise the boost and then sight the increased boost as the gain from the cat removal when they aren't really related.
 
#18 ·
I might have been misleading in my assertion. I dont think that you will get HP gains out of the Up pipe cat delete, but you stand a chance to gain better flow out of it, and you also reduce the risk of your cat disintegrating and going into your turbo and then into your engine (I understand that it is not a very common occurrence, but it is still possible).
 
#20 ·
From what i've researched, usually aren't aftermarket UP's the same diameter as even the stock one? Or barely larger? If you gain HP out of the UP it's going to be hardly squat, sure it MIGHT spool sooner, but it's not going to be noticeable; right? Maybe 1/2 a hp? With a tune.

And YES! the DP is probably THE singlemost restrictive peice in the system! Some vehicles can gain up to 30-50whp (with or even without tunes)
 
#21 ·
Not all UPs' are the same. Especially if your getting the 3" inlet for a turbo that needs that upgrade. SPT SRI's claim to give about 1 extra PSI if I'm not mistaken and slightly quicker spool. But, I don't think it's going to convert to any real gains...because its just the turbo spooling quicker.
 
#22 ·
How would an intake raise the boost on it's own? It's going to magically hold the wastegate shut? If they claim that, they're idiots.

awd4life said:
I might have been misleading in my assertion. I dont think that you will get HP gains out of the Up pipe cat delete, but you stand a chance to gain better flow out of it, and you also reduce the risk of your cat disintegrating and going into your turbo and then into your engine (I understand that it is not a very common occurrence, but it is still possible).
This is true. It is a mod that needs to be done prior to getting a larger turbo for the 02-05s for sure. It's just not going to deliver gains on it's own on an otherwise stock WRX.
 
#23 ·
ok, correction. I think they're claiming it acts like a 1 psi increase. Not that it actually makes a psi change because of the quicker spool. Sorry, if I didn't explain that properly.
 
#27 ·
nope... didnt bother then. but ive had a remap since. that MIGHT have been what it was... but i have no idea. It was weird because ive read countless posts of people saying the Downpipe makes a huge difference, and when i did mine, i was just like... wtf? but maybe thats what it was...
 
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