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Discussion Starter #1
Will the JDM Intercooler fit on the USDM STI motor?

I know some will rant and rave at how this is such a waste, and that I should try other aftermarket intercoolers if I want performance gains, but I am not looking for substantial gains. I may upgrade my ECU software down the road and install an APS exhaust, but that is it.

If I retain STI branded parts, then I will be less likely to be subject to scrutiny or harassment about modifications by a dealership. I would even be willing to wager that the dealership would not be able to distinguish the subtle difference between the USDM and JDM intercooler (which I think is about a 15% size difference).

Anybody know for sure whether it will fit?
 

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Discussion Starter #2
It is wierd posting an answer to your own question, but it seems like it will work:

RalliSpec.com @ [url said:
http://www.rallispec.com/product-engine4.htm[/url]]The JDM STi intercooler has a 40% dimensionally larger core size then the stock WRX (and 15% dimensionally larger core size then the US STi). The result is a 14% improvement in intercooler efficency (on WRX). This improved cooling provides a denser charge and allows more agressive tuning without detonation. Note: requires some modification to the routing of the A/C lines along the firewall of the LHD WRX & STi models. Also A/C lines should be carefully protected against damage due to chafing against the intercooler.

In order to make full use of the intercooler it is necessary to replace the intercooler inlet piping, the hood scoop air splitter (duct), and the intercooler seal with the STi parts. We have packaged these items together with the intercooler in one low cost kit. It is also necessary to install the larger STi hood scoop which we have available separately.

RST-0720kit -- STi Intercooler Conversion Kit for MY02-03 WRX -- $795
RST-0722kit -- STi Intercooler Conversion Kit for MY04 WRX -- $795
(Emphasis added)
 

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Discussion Starter #3
Assuming everything remains constant in determining intercooler efficiency, then upgrading from a USDM to JDM STI intercooler may produce a 5.625% increase in intercooler efficiency. I am inclined to think that even this number is overstated, and actually lower, because the USDM intercooler is already efficient (in contrast to the WRX one) so any increase in size over the USDM unit may not not reflect the same sort of improvement seen in the WRX application (taking the size increase into account as I did when I came up with the 5.625%). I will defer to others who know more on the subject.

My rudimentary calculation comes from the following:

40% increase = 14% increase in efficiency
15% increase = X% increase in efficiency

If we solve for X, X = 5.625%

My math could be off and this calculation may not actually be correct for determining intercooler efficiency.

Any thoughts?
 

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would it be worth a 5% increase? Rerouting your AC, changing your IC piping? I'd just as well save up for an FMIC or an aftermarket TMIC that fits the stock setup... very good find (especially since it could be used under warranty and backed by subaru), but Im not sure how much of a price/power gain it'd be. Kinda wierd how we have more displacement, yet we get the smaller intercooler... granted we arent running as high of boost, but... still. Also sorry not trying to post steal, but what turbo (and psi) do the JDM stis use?

Robert~
 

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From the measurements I took and the measurements I saw on the Jap Spec STi TMIC it seems the USDM STi TMIC is about ~1/2-3/4" shorter (top to bottom) than the jap spec. When I installed my knocklink sensor I took off the TMIC and it was quite tight between the AC line and the TB hose. I think our TMIC might be a bit smaller to accomadate for the larger/longer/taller DBW TB (drive-by-wire throttle body). As such I think the USDM TMIC is smaller to accomdate for this and fitting a jap spec STi TMIC might be a bit tough.

Just my thoughts on this.
 
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