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Hybrid engine build questions


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I am planning a hybrid engine build. I plan to use an EJ251 short block with EJ25D heads to swap into my 97 Outback. Which intake manifold should I use? The manifold from the DOHC engine or from the SOHC engine? Will this run on a stock computer or is a custom tune needed? Are there any other quirky problems I may stumble across? Any known problems I should address while the engine is apart? Thanks for any info.
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Man, I have been wanting to do this build for a long freaking time.... Lame.

 

Okay, well, you obviously have to use the intake manifold for the 25D heads. It will run on the stock computer but I would at least try and get a 2.5 ECU from somewhere.

 

When you put the engine together, make sure you use the EJ25D MLS gaskets (preferably OEM or Cometic) ONLY. The 251 gaskets are different and not MLS. Just make sure you use quality parts, and do the job right the first time. I'd replace the timing components and water pump while your in there, as well as the rear oil/air separator plate.

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Lol, I knew you'd say that. Those were prices quoted to me by a well known local shop that builds high hp subaru engine for sand rails, racing, airplanes. The $700 for each head is crazy expensive. They know what they are doing though but you have to pay for it.
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I work for a salvage yard so I am getting the short block, heads, and intake for $100. I plan to do all the standard timing related stuff as well as all the gaskets and seals. I want to build the engine without spending a huge amount of money. And as soon as my pocket book allows, I will do a full exhaust then have a custom tune done.
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I am planning a hybrid engine build. I plan to use an EJ251 short block with EJ25D heads to swap into my 97 Outback. Which intake manifold should I use? The manifold from the DOHC engine or from the SOHC engine? Will this run on a stock computer or is a custom tune needed? Are there any other quirky problems I may stumble across? Any known problems I should address while the engine is apart? Thanks for any info.

 

This is what is required to run that combination:

25D heads.

25D intake manifold.

25D sensors (ALL of them).

25D crank gear.

25D head gasket (MLS & don't use anything less).

251 short block.

 

This combination will run on a stock EJ22E computer due to the 25D sensors & crank gear being the same as those used in the 22E. However, a 25D ECU would run that combo best. Unfortunately, the connectors for the 95 22E ECU & the 96+ECU connectors are not the same, so it has to be wired up.

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I am putting this engine into a 97 Outback that came with the EJ25D. I bought the car from work with a bad engine (blew the timing belt). Rather than try to rebuild the stock engine, I figured this would be a great opportunity to experiment with a frankenmotor. I've heard this combo (with a tune and exhaust) should put me near 190-200hp at the crank. Can anyone confirm this?
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  • 2 months later...

I don't have dyno numbers but this is exactly what i'm running in my 97gt. I used the 25D heads and 25D IM w/ 251 block and pistons. I used 11044AA642 HG's (ref attached). Pretty sure I used the 251 crank gear (more info on why this mattters?????) though could explain my random misfire i get every now and then. I'm also running stock 25D ECU/tune. Only other problem I had was putting the PCV together. 251 port on the top of the block didn't work with the hoses I had so I had to just use a 5/8" water outlet adapter. Engine has great top end but lacks some bottom end might be all the holes in the exhaust (next project :rolleyes:) oh and make sure you adjust the valves BEFORE you put the engine in. I rushed it getting the engine in and didn't ended up just letting IAG do it.

 

BTW Here's some Pics that might help you

EJ_cr_matrix (1).pdf

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I did this same build also. EVERYTHING is from the EJ25D besides the block, pistons, rods and crank and headgaskets. Headgaskets are from an 06 sti. You cannot tune our ecus.

 

Car had more throttle response but it was not anywhere near a turbo'd subaru.

 

For me it was the same price as a stock rebuild so it was definitely worth it.

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The reason the crank gear matters is because the crank signal comes from it. If you don't have the right one the car won't even start. The stock is a 6 pickup points while newer turboed models have a 36-2-2-2 setup on the crank gear.

 

The 251 most likely has the same crank gear but to be safe and make the ecu happy use the oem gear that was paired with the ecu.

 

I doubt your misfire is from this issue. The 2 are worlds different.

 

Sent from my S3

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I finished my build last weekend. I used a '02 EJ251 block and internals with the heads from a '97 EJ25D. I put it in my '96 Outback. The car originally came with the HLA version of the EJ25D. There was a only a couple minor issues I ran into. I used the intake from the stock engine but had to change the aluminum coolant pipe bolted to the block (the stock pipe had a sensor that the newer pipe didn't have). I also had to change the knock sensor and crank position sensor to connect to the stock engine harness. I am currently running it on the stock '96 ECU (which came with the HLA version of the 25D and was recommended to run on 91 octane). I am going to connect the ECU from a '98 Outback (with the bucket lifter heads and only required 87 octane) to see if it runs any better or worse. The engine seems stronger than the stock EJ25D in my sedan and pulls much better in the low end. Next step is a header and exhaust.
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