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Discussion Starter · #1 ·
Well I've got a 99 2.5rs with a full 04 STi swap. I put on an off the shelf stage 2 tune that works perfectly on my friends 04 STi but on my car I get knock up top and I'm also 2-3 lbs down on boost all the way through each gear.

Could it be that my top mount isn't getting enough airflow because of the small hood scoop and lack of splitter and causing this? Anyone else having issues?

ALSO, where can I find a front mount intercooler to fit a gc8 with an sti motor? I don't want to get one but I might have to.

Any input would help.
 

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2006 WRX
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611 Posts
You can get a larger scoop for the GCs. I'm not sure where, but there's a local guy with a huge scoop on his '01 RS with a monster turbo build. You can also use the STI splitter on the RS with a bit of modification.
 

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project blackbird.
'01 RS, '81 Fiat Spider
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3,396 Posts
Well I've got a 99 2.5rs with a full 04 STi swap. I put on an off the shelf stage 2 tune that works perfectly on my friends 04 STi but on my car I get knock up top and I'm also 2-3 lbs down on boost all the way through each gear.

Could it be that my top mount isn't getting enough airflow because of the small hood scoop and lack of splitter and causing this? Anyone else having issues?

ALSO, where can I find a front mount intercooler to fit a gc8 with an sti motor? I don't want to get one but I might have to.

Any input would help.
Try the splitter first. It will more evenly distribute the airflow over the intercooler, especially at high speed.
 

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2003 Outback Sedan H6
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2,274 Posts
I doubt that's the reason you're knocking. I've never heard of anyone having cooling issues with the stock GC8 scoop. A splitter would help though since it would direct air into the intercooler better, rather than pushing the air around it.
 

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BRP ver5 RSTi, Beater Leggy
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370 Posts
Every engine is a little different, even the exact same model make/year.

That being said, I don't think it's the lack of a splitter giving you trouble. I've seen plenty of 02+ wrx's running with sti IC and no splitters and they are fine.

I'd check for a boost leak. Make up one of those PVC pipe boost leak testers and hook it up and check - not more than 10 bucks to make and about 2 hours or so.

If you're getting knock, the ecu will retard timing and boost to keep your engine from blowing up also, which is probably what you're seeing. Probably not a good idea to run that off the shelf map if it's audibly knocking.

As for the splitter, one option I've seen for GC's to run GD+ sti TMIC is to get your hands on an 04+ splitter, hack off the top part and re-drill it to fit the GC hood scoop. This is probably what I'll be doing sometime down the line.
 

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Discussion Starter · #7 · (Edited)
Yeah, I'm not sure that I could change the classic look of the gc front end.

In my case doesn't it kind of make sense that the car would knock up top in 4th because of heat soak? And let me clarify, when I say it knocks what I really mean is the ECU is pulling 1 to 4 degrees of timing because it detected some form of knock. I was logging the runs.
 

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Discussion Starter · #8 ·
The reason why I am stressing is because I want to get a protune but I don't want to waste a $500 tuning session because my car has this problem on the dyno. I need to know if I should invest in a FMIC before the tune and pinpoint the problem beforehand. I can't just count on the tune curing the problem.

It's wierd that my car would pull timing for knock when it's never even hitting peak boost for stage 2.
 

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2003 rs2.5 BRP
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831 Posts
why don't you put your stock tune on it.. and see if it knocks. if it's knocking then it might be something other than your tune.. if thats what you are thinking, also check for boost leak as previously mentioned. Then again, you might also want to try resetting your ecu.
 
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