Question about Bellmouth and turbo - Subaru WRX Forum
 
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#1 Old 07-20-2005, 06:00 PM
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Question about Bellmouth and turbo

I was told that if you are using a "Bellmouth Downpipe" you need to port the turbo to take full advantage of the pipe. Has anyone else heard this or done this? What kind of results did you get if so?
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#2 Old 07-20-2005, 06:53 PM
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No, you don't need to. Some people say you need to on the STi turbo (which is different from the WRX turbo) but I have heard just as many people say you don't need to.

And, no, you don't need to on any other aftermarket turbo that I've heard of.
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#3 Old 07-20-2005, 09:01 PM
 
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Many people get boost spike to about 20-22 psi w/ a bellmouth on the STi. Porting the wastegate fixes that, but like Cosmo says, for some reason it doesn't happen to all STi's w/ bellmouth DPs.
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#4 Old 07-24-2005, 01:02 PM
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My STi is currently stock, but within the next week or so I will be hopefully be installing a TBE and maybe a new up pipe. The shops in my area do not have much experience with STi's and therefore I'm sorta concerned by talk about boost creep and cat or no cat (emissions testing) recomendations. Does anyone have any advice for bellmouth (like the Invidia) or separated (like the Perrin) downpipes to prevent creep and cat or no cat for MN?
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#5 Old 07-26-2005, 06:20 AM
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just do bellmouth and why bother changing your uppipe when you don't need to. It's already catless and u won't gain anything from changing it...
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#6 Old 07-26-2005, 11:02 AM
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Quote:
Originally Posted by gingertooth
just do bellmouth and why bother changing your uppipe when you don't need to. It's already catless and u won't gain anything from changing it...
You are not correct. Unless the WRX is different than the STI there is a cat in the up-pipe. It is a 'pre-catalytic converter'. Changing the UP therefore will eliminate the first of 3 cats in the stock WRX and STi exhaust system and therefore I should get faster spooling and better flow just to name a few advantages. Anyone else have more insight and good info to help with this question?
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#7 Old 07-26-2005, 05:49 PM
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are u positive. i thought the sti didn't come with one in the uppipe.
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#8 Old 07-26-2005, 07:32 PM
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Quote:
Originally Posted by gingertooth
are u positive. i thought the sti didn't come with one in the uppipe.
Thats what I thought too?

My turbo's fixed and a lot better =)
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#9 Old 07-26-2005, 11:07 PM
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i could have swore there was no cat in the up-pipe of an STi.
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#10 Old 07-27-2005, 07:34 AM
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Quote:
Originally Posted by PrimeTimeSTi
You are not correct. Unless the WRX is different than the STI there is a cat in the up-pipe. It is a 'pre-catalytic converter'. Changing the UP therefore will eliminate the first of 3 cats in the stock WRX and STi exhaust system and therefore I should get faster spooling and better flow just to name a few advantages. Anyone else have more insight and good info to help with this question?
You are incorrect. The STi and WRX uppipe are different. The WRX uppipe has a cat. The STi uppipe doesn't.
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#11 Old 07-29-2005, 12:23 PM
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Quote:
Originally Posted by Cosmo
You are incorrect. The STi and WRX uppipe are different.


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