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Old 03-07-2003, 05:41 PM   #1
wackie
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Question JDM WRX 9:1 CR Piston Design

Does anyone know what the top of the piston looks like on the JDM WRX with a 9:1 compression ratio? Is it flat like the STI or have a dish? Anybody happen to have any pics?

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Old 03-08-2003, 12:49 AM   #2
zaxrex
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Default Don't know about the comp ratio, but


that was from a post here
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Old 03-08-2003, 01:15 AM   #3
wackie
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Thanks for the comparison, but I was looking for the JDM WRX that is a 9:1 compression ratio. If that's a piston from the USDM WRX it's 8:1. The reason being, the shape of the top of the piston is going to have a lot of effect on how much money I'm going to have to spend on gas with my new motor.
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Old 03-10-2003, 12:05 PM   #4
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Check that link,

"the internals as compared to an EJ207 2002 JDM STI block "
for sure not a US spec STi.

Again I can't say anything to the Compression Ratio for the EJ207.

If worse comes to worse, you can contact the guys that did the write-up for more tech info.
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Old 03-10-2003, 12:11 PM   #5
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I believe the compression ratio on that STI is 8:1. The reason I asked for the 9:1 CR version is there is a version of the EJ20 in a WRX (not STI) in Japan that runs a 9:1 CR along with the TD04 turbo. I just wanted to see what the piston design looked like.
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Old 03-10-2003, 02:44 PM   #6
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Quote:
Originally posted by wackie
Thanks for the comparison, but I was looking for the JDM WRX that is a 9:1 compression ratio. If that's a piston from the USDM WRX it's 8:1. The reason being, the shape of the top of the piston is going to have a lot of effect on how much money I'm going to have to spend on gas with my new motor.
If I'm reading this right, you're having custom pistons made to produce a 9:1 static ratio, and you're concerned about the frame propagation within the chamber, i.e. efficiency vs. detonation? If money were no object, I'd tell the piston manufacturer I wanted a copy of the crown of the STi pistons, yielding a 9:1 cr, then run alcohol injection. Done.
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Old 03-10-2003, 02:54 PM   #7
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Quote:
Originally posted by n2xlr8n
If I'm reading this right, you're having custom pistons made to produce a 9:1 static ratio, and you're concerned about the frame propagation within the chamber, i.e. efficiency vs. detonation?
Well, you're close. I just purchased a JDM WRX engine for pretty cheap (with 9:1 CR from the factory) and I was curious about efficiency vs. det. in that particular engine. I was just trying to get a gauge of where I would end up while tuning (and hoping the piston was designed like the STI one). The engine is being used for temporary pleasure while I build up a custom 9:1 engine that's sleeved, closed deck, forged pistons/rods, yadda yadda.
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Old 03-10-2003, 03:04 PM   #8
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Quote:
Originally posted by wackie


Well, you're close. I just purchased a JDM WRX engine for pretty cheap (with 9:1 CR from the factory) and I was curious about efficiency vs. det. in that particular engine. I was just trying to get a gauge of where I would end up while tuning (and hoping the piston was designed like the STI one). The engine is being used for temporary pleasure while I build up a custom 9:1 engine that's sleeved, closed deck, forged pistons/rods, yadda yadda.
Well, I hate pat answers, but it would depend heavily on whether or not the JDM WRX combustion chambers are the same as the ones you plan to use on the nastie. Short answer: run alcohol and love it.
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Old 03-10-2003, 05:33 PM   #9
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Hey wackie,

We have the same engine going into one of our cars. Though like you said we are not sure about the internal work of the engine, wether it is similiar to that of the USDM WRX or that of the JDM STi. Though We would really love it if it was similiar to that of the STi.
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Old 03-10-2003, 05:37 PM   #10
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Yeah, Adam told me you were getting one of those. You've actually got my car (and my new flywheel) sitting at your shop. My engine should be there this week. If you want to find out what the engine looks like inside, feel free. Just don't charge me for the labor.
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Old 03-10-2003, 06:39 PM   #11
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Well I don't think we will be taking it apart. But as soon as I get mine in I will be tuning it with the EcuTek. Yeah AVCS... So if you were thinking of tuning it even though you are going to be upgrading to another block I will probably have a fairly good map for it.

Bill
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