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Old 05-10-2003, 07:22 AM   #1
Cusco
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Member#: 6220
Join Date: Apr 2001
Location: Gresham, OR
Vehicle:
99 ej25sett/TEC II
-:GaraGe ChimEra:-

Default Will this work? MY99 Block w/ MY00-01 RS or 02+ WRX DOHC head swap???

I have a MY99 RS and I wanted to change over to the MY00-01 DOHC heads and rear LSD. I was wondering how feasible it was to change the heads on the engine. I am running a TEC2 so engine management isn't and issue. I was guessing that all you had to do is replace the heads, get new timing belts, set timing correctly and run engine? I may be thikning in to simple of terms but I thought the only issue of going from SOHC to DOHC was that the MY99 ECU was not compatible with the MY00-01 ECU since both ECU;s are programmed to run differnet engines. Since I am running the TEC2, timing as well as all Engine management is controlled by the TEC 2, right? As long as the engine it self is built right and the timing is correct the engien should run?

The second question is if it is feasible to add the WRX heads on a MY99 EJ25 short block. DO they even match up? The reason I want to do this is so that I have heads that are capable of revving higher then the 6400RPM rev limit on the MY99 SOHC engines. I know the heads are not built for revving over 6500RPM max on stock head internals.

I guess my quesiton is which is better swap for flow and high revs, the MY00-01 DOHC RS head or the 02+ WRX DOHC. Do I swap or is it cheaper to just go with aftermarket valves, valve springs, and retainers?

If aftermarket is the way to go which is best? COBB? Any suggestions?

Thank you so much.

John

Twin-turbo EJ25 (aka ej25sett) @10 psi
blown headgaskets...
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Old 05-12-2003, 12:52 PM   #2
Jaxx
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Join Date: Aug 1999
Chapter/Region: NWIC
Location: Boise,Idaho,USA
Vehicle:
The 93 Imp W/EJ20K
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Quote:
I may be thikning in to simple of terms but I thought the only issue of going from SOHC to DOHC was that the MY99 ECU was not compatible with the MY00-01 ECU since both ECU;s are programmed to run differnet engines. Since I am running the TEC2, timing as well as all Engine management is controlled by the TEC 2,

the cam position sensor is not a big deal as you are using the tec 2 which does not use it ..
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Old 05-12-2003, 03:26 PM   #3
OBSbug
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Join Date: Feb 2001
Chapter/Region: NESIC
Location: The 'bury of Tewks
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2011 Legacy 2.5i
Hot Tamales Red

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Not to nit pick, but the DOHC heads were only on the 98 RS as far as imprezas go. As far as WRX Heads vs DOHC 98 Heads vs Upgraded SOHC heads, it depends on what you want to do. Not 100% sure about WRX heads matching up with EJ25 shortblock. If you want to go high revving then you're going to have to upgrade the cams as well as springs, retainers, and possibly valves on the SOHC and DOHC GC8 heads. Again, I have zero experience with WRX heads so I cant comment on how high you can go.

Hope I helped a bit.

-Aaron
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Old 05-12-2003, 07:07 PM   #4
stimpy
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Location: Austin, TX
Vehicle:
2008 STI

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What you need to do is hunt down the old posts by Trey Cobb regarding their EJ25 in their Conebasher. They used a built EJ25 shortblock and then bolted all the other Ej20 components back on. If I remember correctly, they had to massage the quench area on the heads to get them to mate up properly to the larger bore of the EJ25.

-Jon
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