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#2: 02-27-2013, 11:44 PM
DOHCEJ22E1's Avatar
Title: Monkey
Location: Brooklyn, CT.
Car: 1996 Subaru Legacy LSi.
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I've noticed that there are many questions regarding hybrid engines & while I'm not going to go into full detail, I am going to explain the hybrids that I know will work with the stock Phase 1 ECUs that we have here in the United States. If anyone has more info on their hybrid builds, please feel free to chime in. Also, the use of different sized head gaskets will determine the end ratio. I'm just explaining the different types of hybrids on stock head gaskets & head gaskets MUST AT ALL TIMES match the bore of the block. If you have an EJ22 block, the EJ22 head gasket must be used & so on.

Dual Overhead Cam EJ22:
Done by installing EJ25D heads on an EJ22 (E or T).
There is no need to change sensors on the heads of the block since they are the same.
This hybrid has lowered compression (Es have 9:1 while Ts have 7.5:1) from it's original SOHC variant & is better for turbocharging, since it has pretty deep chambers combined with dished pistons.
The DOHC 22Es can be used as they produce a little more midrange power than the SOHC 22Es but the 22Ts should not EVER be used without turbocharging.
The best DOHC heads to use are the 97-99 heads as the chamber is enclosed in the bore of the EJ22's cylinders while the 96 25D chambers are cut to the bore of the 25D & should not be used on any EJ22 block.
This engine can be safely run on 87 octane.
Any Phase 1 ECU will run DOHC heads, even the first generation Legacies.

"Big Valve" EJ22T:
This is done by bolting EJ22E heads on an EJ22T block.
The compression ratio doesn't change much but the 22E heads have bigger valves, so this helps out w/tq delivery as a little more air is brought in to be compressed.
The heads are essentially the same as the turbo heads but they have to be drilled & tapped for turbocharging.
You must also use the 22T camshafts in this build as they have profiles for the turbocharger.
The 22T computer will run these heads without an issue.

Single Overhead Cam EJ25D:
This is any 25D block w/EJ22 heads on it (the EJ22 heads have small chambers, which contributes to the high compression).
Again, no need to change sensors.
However, the compression ratio increases tremendously (approaching 11:1), which necessitates 91+ octane be used at all times to keep detonation at a minimum to zero.
There are reports of this hybrid produces 180+bhp & nice tow-end tq.
This would probably be an engine good for rock climbing, mudding, rallying, & "dirty" situations.
The 97-99 25D block provides a lower compression than the 96 block, which has flat top pistons designed for max compression.
Using a 96 25D block may cause some issues with compression being TOO high & require more depth of control, like installing a stand alone ECU.

High Compression DOHC EJ25D:
This is made by installing 97-99 25D heads on a 96 25D block.
Compression is about the same as the SOHC 25D variant & it must be run on 91+ octane also.
The powerband is pretty much an exaggerated version of the 97-99 EJ25D.
This hybrid can run on the stock ECU.

Low Compression DOHC EJ25D:
This is made by installing 96 25D heads on a 97-99 25D block.
Compression is lowered to about 8.8:1/9:1 & makes this engine good for turbocharging but on the flipside, the heads do not allow very high revs.
Power produced is more or less that of a 96 25D.
This engine can run safely on 87 octane & on the stock ECU.

I only have pictures of my DOHC EJ22E hybrid but I have seen the hybrids I have mentioned (haven't seen a 96 25D SOHC yet) & they all seem to work well but the SOHC 25Ds grant the most power & low-end tq out of all the builds & are easier to maintain, since they have the simplicity of the SOHC design.

Hope this helps anyone who wants to have general info on EJ hybrids.
I am also going to explain this.
When using 2.2 heads on a 2.5 block, MAKE SURE that they are ported & polished (at the very least ported) or you will not be able to get the power you're expecting from the high compression combo.

Last edited by DOHCEJ22E1; 02-28-2013 at 07:01 PM..
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