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Old 02-02-2011, 03:17 PM   #1
qtr_wrx
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Default PII ej25 hg thickness?

hello guys

I'm looking for a simple way to increase my na ej25 CR without going into pistons/shaving heads stuff! So I was thinking about a thiner hg

I was woundering what the oem hg thickness?
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Old 02-02-2011, 07:56 PM   #2
T Wrex--OH
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Stock head gasket thickness is 0.030 inches

Sti head gasket thickness is 0.020 inches
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Old 02-03-2011, 06:49 PM   #3
qtr_wrx
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thanks for the help. Do you know by how much points the CR will go up using sti hg?
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Old 02-03-2011, 10:59 PM   #4
T Wrex--OH
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From 9.88 to 10.15.

That is according to my TWE compression calculator.
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Old 02-03-2011, 11:26 PM   #5
ballitch
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IIRC the sti gasket is thicker. The N/A SOHC Phase II EJ25 HG is .60mm thick. If i'm not mistaken, the STi HG is 1.0mm thick. Anyone know for sure? Search button here I come...



~Josh~


FYI, sti gasket apparently is .60mm thick.

Last edited by ballitch; 02-03-2011 at 11:37 PM. Reason: found info, .....
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Old 02-03-2011, 11:37 PM   #6
T Wrex--OH
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Quote:
Originally Posted by ballitch View Post
IIRC the sti gasket is thicker. The N/A SOHC Phase II EJ25 HG is .60mm thick. If i'm not mistaken, the STi HG is 1.0mm thick. Anyone know for sure? Search button here I come...



~Josh~

Sorry man, I know this info is accurate.

0.75 mm for Phase II SOHC

0.50 mm for EJ25 STI

I know lower compression ratio of STI engine would suggest otherwise about the gasket thickness, but this is how it is.
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Old 02-03-2011, 11:38 PM   #7
T Wrex--OH
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....But, the EJ25 DOHC on the other hand

1.50 mm thick head gasket.
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Old 02-04-2011, 12:14 AM   #8
ballitch
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Quote:
Originally Posted by T Wrex--OH View Post
....But, the EJ25 DOHC on the other hand

1.50 mm thick head gasket.
Well I knew that one...lol.

Not trying to say you're wrong, but just to be sure i'll throw my digi calipers on a new set of Phase II HG's and see what it says.



~Josh~
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Old 02-04-2011, 12:44 AM   #9
T Wrex--OH
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I'm getting conflicting search results now.

I know the STI head gasket is indeed thinner, but by how much, I dunno.

Please, I'd like you to measure the gaskets with a caliper, I'm curious now.

I would do it, but who knows when I'll get my hands on them.

If you do measure the phase II gaskets, please include the part number.
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Old 02-04-2011, 12:19 PM   #10
Bluefoton
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I changed my stock HG 11044AA633 for an STI one - 11044AA642. Forgot to asked the tech to measure but he said the crushed thickness of the STi one is greater

Would love to get actual values though and see how my CR changed

Last edited by Bluefoton; 02-04-2011 at 12:45 PM.
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Old 02-04-2011, 02:23 PM   #11
qtr_wrx
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Quote:
Originally Posted by T Wrex--OH View Post
From 9.88 to 10.15.

That is according to my TWE compression calculator.
wow thats almost half point using oem parts.
Comteic make custom hg, right? I wounder if they make 0.010 inches to bump the CR up
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Old 02-04-2011, 02:45 PM   #12
T Wrex--OH
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Quote:
Originally Posted by Bluefoton View Post
I changed my stock HG 11044AA633 for an STI one - 11044AA642. Forgot to asked the tech to measure but he said the crushed thickness of the STi one is greater

Would love to get actual values though and see how my CR changed

I wonder if the tech just looked at it and assumed it was thicker because it's multi-layered steel, as compared to the original, which is only single layered. I highly doubt he actually measured it.

I do not think the STI gasket is thicker. Possibly the same thickness, but definetely not thicker.
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Old 02-04-2011, 04:12 PM   #13
Bluefoton
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Found info! Bottom of the page...

http://www.b4et.com/docs/090618_ej_c...tio_matrix.pdf

Number crunching: If my HG went from 0.65 to 0.56mm for a stock CR of 10:1 my new CR is...?
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Old 02-04-2011, 07:19 PM   #14
T Wrex--OH
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Quote:
Originally Posted by Bluefoton View Post
Found info! Bottom of the page...

http://www.b4et.com/docs/090618_ej_c...tio_matrix.pdf

Number crunching: If my HG went from 0.65 to 0.56mm for a stock CR of 10:1 my new CR is...?

Nice find! What engine you have? SOHC EJ25?
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Old 02-04-2011, 10:51 PM   #15
T Wrex--OH
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So if I plug in the bore and thickness of the gasket into the EJ25 SOHC, I get a final compression ratio of 10.19:1.

Not a bad bump in compression.
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Old 02-05-2011, 12:44 AM   #16
Bluefoton
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Thanks! Yes, I have a SOHC EJ251, 10:1... now raised to 10.2 :

Curious though ,where the heck do you plug these numbers in?
I'll have to do some logs soon to check if, with the increased compression, running 89 octane instead of 87 affects timing. Oh and some random online calculator stated that a .2 compression increase = +1hp....
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Old 02-05-2011, 01:42 AM   #17
ballitch
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Google search "compression ratio calculator", take your pick. I use a site named not2fast.com Has a bunch of other links and info on the site that's fun to read up on.



~Josh~
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Old 02-05-2011, 03:12 PM   #18
T Wrex--OH
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I have a .2 increase in compression too, yay! I'm plugging my numbers into an excel sheet made by Tech Works Engineering. Just google "twe compression calculator". It works great.
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