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Old 03-17-2008, 12:31 PM   #1
irascible
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6SPD Cornfed GT30R

Default piston/rod combo

I have an '06 WRX, and i'm trying to find out what vendors sell a long rod combo with an offset wrist pin for the best price.

I'm not too concerned if they are 4340 or 2618, but if the price difference is marginal.. i'd of course go with 2618.

And yes, i've been reading the FAQ's, and searching this forum for a while. The vendors I found don't seem to supply them anymore or aren't listing them on their sites, cobb being one of those.

Thanks
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Old 03-17-2008, 03:48 PM   #2
Devan M
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Make sure you get the correct dish volume for your 06 WRX heads, they are different than the STI
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Old 03-17-2008, 04:12 PM   #3
irascible
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Originally Posted by Devan M View Post
Make sure you get the correct dish volume for your 06 WRX heads, they are different than the STI

Thanks, but why would that matter?
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Old 03-17-2008, 04:41 PM   #4
MartinSTi05
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The WRX has a smaller combustion chamber volume. If you were to use pistons for an STi app, your compression would be raised significantly over stock. In order to main ~stock CR you need a larger dish than a standard STi piston if you are using WRX heads.
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Old 03-17-2008, 04:46 PM   #5
irascible
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Originally Posted by MartinSTi05 View Post
The WRX has a smaller combustion chamber volume. If you were to use pistons for an STi app, your compression would be raised significantly over stock. In order to main ~stock CR you need a larger dish than a standard STi piston if you are using WRX heads.
I can't find any piston manufacturer that has pistons with a different dome cc for the wrx vs STi? To the best of my knowledge, both are inset dome pistons, and the STi is -22.2cc, i'm uncertain what the wrx is. Theoritically, that would mean it would actually lower the compression if I used the STi pistons, correct?

I'm still looking for a long rod/piston combo, or if anyone can help point me in the right direction on where I can buy the parts individually... that would be great as well. I'm not savvy enough to order custom pistons/rods.

Last edited by irascible; 03-17-2008 at 05:28 PM.
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Old 03-17-2008, 05:46 PM   #6
MartinSTi05
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NO, the STi piston uses a smaller dish volume piston, because it has a larger combustion chamber than a WRX head. If you were to use a small dish volume STi piston with a small volume WRX combution chamber the compression would go up.
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Old 03-17-2008, 06:17 PM   #7
bluemax189
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in 06/07 its basically the same internals as an STI. Both are 2.5liters. From the factory in 06 and 07, the wrx had a slightly larger Compression ratio, so.......using 2.5 sti pistons should be fine. Maybe for the 02-05 the wrx 2.0 engines, it might cause some problems, but you will be fine on your 06. Im assuming this is what martinSTI05 is thinking of.
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Old 03-17-2008, 07:25 PM   #8
irascible
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Originally Posted by bluemax189 View Post
in 06/07 its basically the same internals as an STI. Both are 2.5liters. From the factory in 06 and 07, the wrx had a slightly larger Compression ratio, so.......using 2.5 sti pistons should be fine. Maybe for the 02-05 the wrx 2.0 engines, it might cause some problems, but you will be fine on your 06. Im assuming this is what martinSTI05 is thinking of.
I agree, I think that's where the confusion is too. The pistons are the same in these years from what I can find. This would also explain why all piston manufacturers list them as ej25 and only have one design.

Now, the heads are different and have a smaller CC than the STi which is why they have a higher CR.
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