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Old 04-15-2009, 09:55 PM   #1
Zac86
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Member#: 136919
Join Date: Jan 2007
Chapter/Region: W. Canada
Location: North Pole
Vehicle:
2005 Legacy GT Wagon
ABP

Default Questions about EJ25/EJ22 Hybrid High Compression engine

looking at doing this build myself in the near future. Can use any EJ25 bottom end? is there a better one? Also about the EJ22 heads? what year is the best? I also heard you can use a EJ25 ECU to raise the revlimit another 500RPM? This engine will be going into my 98 legacy which currently has a EJ22. Will using a phase 2 EJ25 ECU remove my need to have a MAF sensor?
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Old 04-15-2009, 10:06 PM   #2
PhilSine
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Join Date: Oct 2006
Chapter/Region: MWSOC
Location: Superior, WI
Vehicle:
02 WRX Wagon (WRB)
98 OBS-T, 91 Legacy SS

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Compression could be around 10.6:1 depending on which pistons you use. If you used a thin enough Cometic head gasket you could get as high as 11.9:1 or so.

I don't know enough about head gasket particulars to offer any pro vs con advice with respect to thickness.

I think the biggest problem you'd run into is the fact that the EJ22 SOHC heads may not flow enough air to really be able to accomodate the increase in compression in NA form. I have no data on this so it is something you'd have to explore further.

For all those wondering, I have a compression ratio calculator spreadsheet made up by Matt Jones (of NASIOC) but I am uncertain of just how accurate they are. I have run the math to check his calculations on various set-ups based upon information I found published and my numbers were often very close to his.

Also...

You can raise the rev limit in your 98 EJ22 ECU by soldering in a larger crystal that controls the rev limit. It's very easy to do and cheap too.
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Old 04-15-2009, 10:10 PM   #3
Zac86
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2005 Legacy GT Wagon
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Quote:
Originally Posted by PhilSine View Post
Compression could be around 10.6:1 depending on which pistons you use. If you used a thin enough Cometic head gasket you could get as high as 11.9:1 or so.

I don't know enough about head gasket particulars to offer any pro vs con advice with respect to thickness.

I think the biggest problem you'd run into is the fact that the EJ22 SOHC heads may not flow enough air to really be able to accomodate the increase in compression in NA form. I have no data on this so it is something you'd have to explore further.

For all those wondering, I have a compression ratio calculator spreadsheet made up by Matt Jones (of NASIOC) but I am uncertain of just how accurate they are. I have run the math to check his calculations on various set-ups based upon information I found published and my numbers were often very close to his.
I'm aware of the heads not being able to flow properly so I'm ready to learn how to PnP properly so the heads flow well all the way up to 7000RPM.
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Old 04-15-2009, 10:13 PM   #4
PhilSine
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02 WRX Wagon (WRB)
98 OBS-T, 91 Legacy SS

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I edited for the rev limit raising so please re-read the bottom of my first post.
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