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Old 07-26-2007, 12:55 AM   #1
boostedscooby2002
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Default JDM V7 heads mated to USDM 2.5 shortblock.

I was just thinking of a possible future setup for my 02 wrx. I tried searching but have not come up with any info. Is this do-able? Or will compression ratio get screwed up? I might have a lead on v7 heads including the ecu.
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Old 07-26-2007, 08:03 AM   #2
chaos311clarity
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it will raise the compression ratio... huff has v8 heads on his 2.5 block and i think hes up around 9.2:1 or something like that.
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Old 07-26-2007, 09:49 AM   #3
ejh25
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Quote:
Originally Posted by boostedscooby2002 View Post
I was just thinking of a possible future setup for my 02 wrx. I tried searching but have not come up with any info. Is this do-able? Or will compression ratio get screwed up? I might have a lead on v7 heads including the ecu.
You will definitely bump up the compression. Somewhere in the 9.2 to 9.5:1 range. I have V8 Spec C heads on a built 2.5L and they flow really well. I have a Helix valvetrain to go along with the Spec C cams and I am using AVCS. These heads are a total PITA to get parts for and when you are in a pinch they can be costly and or not available.

The valve covers and their associated gaskets are specific to the JDM heads. rallispec.com typically has the best price on the gaskets.

The USDM fuel rails, even most aftermarket ones will come into contact with the AVCS on the JDM heads if you are using a USDM manifold and risers. Do yourself a favor and get a one piece JDM intake manifold riser combo so that you get yourself more clearance for the fuel rails.

If you want a great flowing head with AVCS it is a good option but I would think the simplicity of the USDM WRX head with good cams and maybe a mild port job would be the route I would take if I were to do it all over again.
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Old 07-26-2007, 01:00 PM   #4
boostedscooby2002
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Thanks Guys. I think I will pass up on taking this route, going by the information that you have given me. It sounds like too much of a hassle. I don't know if I like the idea of running such a high compression ratio. Maybe I will find some Usdm 2.5 sti heads with the avcs adapters from Gruppe S. My last choice would be to stick with the wrx heads.
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Old 07-26-2007, 02:41 PM   #5
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Quote:
Originally Posted by boostedscooby2002 View Post
Thanks Guys. I think I will pass up on taking this route, going by the information that you have given me. It sounds like too much of a hassle. I don't know if I like the idea of running such a high compression ratio. Maybe I will find some Usdm 2.5 sti heads with the avcs adapters from Gruppe S. My last choice would be to stick with the wrx heads.
Sounds like a plan..although don't discount the increased compression, it does wonders for torque.
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Old 07-26-2007, 10:15 PM   #6
boostedscooby2002
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ejh25.... How hard was it to wire the avcs from your v8 heads to the ecu on your 02 wrx? I assume you had the matching v8 ecu and tuned. Or did you have aftermarket engine management like Hydra?
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Old 07-26-2007, 10:19 PM   #7
ejh25
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Quote:
Originally Posted by boostedscooby2002 View Post
ejh25.... How hard was it to wire the avcs from your v8 heads to the ecu on your 02 wrx? I assume you had the matching v8 ecu and tuned. Or did you have aftermarket engine management like Hydra?
Hydra
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Old 07-26-2007, 11:33 PM   #8
LeoNYC
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what happens to the cr if u use cometic head gaskets with this setup?
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Old 07-27-2007, 08:05 AM   #9
ejh25
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what happens to the cr if u use cometic head gaskets with this setup?
My guess is that you could get a head gasket that lowers the CR or raises it depending on what you want to do...I'm sure there is a limit as to how much the CR can be manipulated.
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Old 07-28-2007, 09:58 PM   #10
jaxscuby
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you could always take off the avcs...
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Old 07-29-2007, 09:14 AM   #11
ejh25
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Quote:
Originally Posted by jaxscuby View Post
you could always take off the avcs...
True...but at that point why not start off with the WRX heads and get some nice cams and a valvetrain...maybe even a mild port.
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