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Old 05-10-2009, 05:53 PM   #26
HamFist
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Member#: 2112
Join Date: Aug 2000
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2000 Impreza 2.5RS
BRP

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Does this combo survive over 18psi of boost?
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Old 05-10-2009, 05:57 PM   #27
sniper512
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Ummm yes its a USDM STI block I should hope so .

Well I guess it would also depend on which turbo is providing the 18psi as well lol.
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Old 05-10-2009, 06:13 PM   #28
HamFist
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No guessing. Does it live...or does it crush pistons due to ****ed up quench and detonation?
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Old 05-13-2009, 12:54 AM   #29
Marnix
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With correct gasket thickness (ie. matching pistons rather than compression ratio) quench will be OK with these heads, combustion chamber design is not far off from EJ257.
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Old 10-23-2012, 10:59 AM   #30
kimokalihi
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91 Legacy SS EJ20G
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Old thread but I'm curious how this would apply to 97 jdm forester ej20g heads? What gasket do I use for these heads? I think the CC of these heads is different from the wrx heads. I've already got them though and I have a 257 shortblock so I'd like to rebuild it with forged pistons and put these hads on and see how my robtune handles it. Rob said it'll be fine and the ecu won't know the differemce. It'll just see more airflow and add more fuel accordingly. Its tuned for 550s and td05.
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Old 10-24-2012, 02:43 AM   #31
Marnix
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You will need the forged pistons for EJ205 WRX heads then compression ratio is acceptable. If you go for EJ257 STI pistons compression ratio is too high to run even moderate boost.
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Old 10-24-2012, 01:45 PM   #32
i_c_the_light
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I'm curious about the 25D gasket. I can't remember for sure but is it quite thick because the 25D piston pokes out above the deck at TDC? So that would be the gasket to go for when mating a 25D to 20H heads?
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Old 10-24-2012, 03:30 PM   #33
kimokalihi
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Quote:
Originally Posted by Marnix View Post
You will need the forged pistons for EJ205 WRX heads then compression ratio is acceptable. If you go for EJ257 STI pistons compression ratio is too high to run even moderate boost.
Ok cool. Which head gasket?
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Old 01-30-2013, 11:57 AM   #34
eph
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Kimo, Looks like we'll both be in for a 257. Subscribed!
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Old 01-30-2013, 10:16 PM   #35
RallyColtTurbo
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If you haven't rebuilt the shortblock yet, why not go with custom pistons? The cost over an off-the-shelf piston is marginal (+20%ish).

That way you can use a standard off-the-shelf head gasket and choose your exact desired compression ratio. All it takes is a bit of math.
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Old 02-10-2013, 03:23 PM   #36
Subbiespeed
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you should look up the thread i had posted about this it should answer a lot of questions
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