So heres the deal.  I aquired a 1997 Legacy with a 2.2 that has bad rings.  So I figure I will do the 2.5/2.2 setup.  I've searched around and I guess I'm not finding the answers I want, what I would like to know is what 2.5 bottom end should I use?  Do I need a DOHC block, or can i use a SOHC block?  Does it matter one way or the other?  I also remember seeing something about different sized oil pumps, as far as volume.  Also which headgasket does this require? Just an OEM 2.5 one?  This legacy is a 5-speed, which clutch/flywheel setup can I use?  Thanks for any info.

Either block will work, but there are some things to note.

96 DOHC block will have the highest compression because the pistons actually crest ABOVE the deck of the block. These blocks need a head gasket of a certain thickness to prevent the piston hitting the head.

 

A 96-98 DOHC block will have 48mm rod bearings which are known to fail.

In 99 they increased thereof bearing size to 52mm, bigger bearing surface, less likely to fail.

If you want to do a rebuild of the bottom end before installing then either one will be fine, but if just using a used block the 96-98 are a bit of a gamble.

 

On the DOHC block definitely use an STI oil pump. More volume for the small rod bearings to prevent failures. On the SOHC block its not as big of a deal, though it is a good idea if you plan to run high RPMs all the time, or if you plan to off-road and run low RPM under moderate to heavy load, like climbing rocky hills.

 

Cometic makes a custom gasket for this build. Somewhere recently someone posted the part number.

If you use a Subaru gasket (which is done all the time) you have to drill/punch some holes in the gasket for a water passage in the head. Not a huge deal.

Cool, thanks for the info. 

Ok, so I aquired an ej25d short block and am confused on which headgaskets I need to use with my 2.2 heads.  They are single port heads (phase 2?).  Which thickness gasket do I use? Or do I get factory ones and drill?

Edited August 26, 201411 yr by CrownLoyale

Gasket thickness depends on which block you have. The early 25D blocks had pistons that crest above the block deck. For those you need a thicker gasket, but I don't remember which thickness.

Call Cometic. They will advise you which gasket to use and supply them, with all the correct passages.

 

O.

Edited August 26, 201411 yr by ocei77

Single port doesn't equal phase 2, if they are the original heads from your car they are phase 1.

 

You need this gasket

 

It comes in various thicknesses depending on what compression ratio you want, within reason anyway. Google the part number at the bottom of the picture to find places to order it from.

Cool, thanks for the info everyone!

So heres the deal.  I aquired a 1997 Legacy with a 2.2 that has bad rings.  So I figure I will do the 2.5/2.2 setup.  I've searched around and I guess I'm not finding the answers I want, what I would like to know is what 2.5 bottom end should I use?  Do I need a DOHC block, or can i use a SOHC block?  Does it matter one way or the other?  I also remember seeing something about different sized oil pumps, as far as volume.  Also which headgasket does this require? Just an OEM 2.5 one?  This legacy is a 5-speed, which clutch/flywheel setup can I use?  Thanks for any info.

How strange, I was literally just thinking about this...

Bought me an EJ22 yesterday, Ill see how far I can get in my parents garage on a college budget.

Definately following this, Im very interested in the EJ25 block EJ22 heads frankenmotor. Ive also done some research, apparently a "reversed frankenmotor" (EJ22 block w/EJ25 heads) is great for turboing the snot out of due to 8.6:1cr.

Ive heard of frankenmotors running around 11:1cr, higher and lower depending on heads, block, gaskets, decked heads, etc.

main worry for me (being a daily driver)... Will it need to run premium?

The compression ratio of the dohc ej22 is more like 8.9:1, but still better for turbo than stock. I'm actually running one, but with eg33 svx pistons and ej22t head gasket so I've got 9.9:1 compression. Let me tell you it's fun, very revy motor (if that's a real word).

 

Any iteration of the ej25 block ej22e head frankenmotor will need premium since it has much higher compression than stock.

Edited August 28, 201411 yr by 86BRATMAN

Any iteration of the ej25 block ej22e head frankenmotor will need premium since it has much higher compression than stock.

Figured as such. Is the power worth the cost/trouble? How much power would it make if it were just a completely stock block and stock heads (maybe decked/polished for longevity reasons)?

Figured as such. Is the power worth the cost/trouble? How much power would it make if it were just a completely stock block and stock heads (maybe decked/polished for longevity reasons)?

Assuming the block is a zero deck, thin bearing, '98 EJ25d with its leaky poorly designed cam seals, oil all over the highway like a paving truck, pouring from the stock DOHC heads. The stock compression ratio of this oil and coolant "sprayer" is 9.5 -1..

 

...so, you can expect at least a 10.5 to 1 ratio with the stock SOHC EJ22 heads as replacement... A definite PREMIUM FUEL situation, with added reliability and about an 8 to 10% power boost...

 

...and... the best part... oil that stays inside the engine, and antifreeze that stays out of the crankcase, cylinders, and exhaust ports.... inside the cooling system where it belongs... these last bits are indeed a priceless result of this marvelous head swap!

 

JT

Edited September 21, 201411 yr by JTCoyoté