I talked to my local used Subaru dealer about constructing a Frankenmotor and he seemed pretty sure that 2.2 heads wouldn't fit on a 2.5 block. Of course, I've done a bit of research on this site so unless we have a bunch of story tellers here, I suspect they fit just fine.

 

The reason he gave for not believing they were compatible was that the 2.5 was DOHC, some of them at least. I didn't want to argue with the guy because I really don't know crap but I really didn't think the cams would have anything to do with the head fitting to the crankcase. Am I right on this one?

 

Is there any reason any of the 2.2 engines wouldn't be compatible with any of the 2.5 engines? In fact...is the difference between the 2.2 types outside the block? Ugh, it is, isn't it? It won't matter at all what 2.5 short block I get, they'll all be exactly the same.

 

I think I just answered my own questions didn't I?

 

-Thanks.

Any EJ head bolts up to any EJ block. But make sure that when using a closed deck block, the coolant patterns of block, gasket and head match. Also check if the head combustion chamber matches the cylinder bore of the block you intend to use if you plan to run a head of a bigger engine on a smaller block, extreme example EJ25 block and EJ18 head.

 

Always use the head gasket that matches the block (due to cylinder bore).

Not all EJ25 blocks are the same - but the frankenmotor generally consists of the EJ25D block with EJ22E heads (from any year you desire). The reason the 25D is used is because the pistons are taller and provide higher compression than the EJ251 and up. That and the EJ25D is the cheapest of the 2.5 blocks.

 

Your local dealer doesn't know much about Subaru engine's apparently. But that's not uncommon - they don't do many engine tear downs and they surely haven't ever tried to fit a part from a 2.2 to a 2.5 - there would be no reason for them to do this.

 

The DOHC head design goes all the way back to the first EJ20's built in the late 80's. The DOHC/SOHC has nothing to do with the head fitting to the block - only the way the cams fit to the heads. All EJ 4 cylinders have the same head/block mating with only minor changes in cooling ports, etc.

 

GD

yeah dealers are not in the business of swapping/interchanging parts. they're the worst source for info of that type, i would never think to even ask them even though some are very competent. if one happened to be familiar with stuff like this, that would be the exception, not the rule.

Good, I'm glad he's probably not an idiot. He seems like he knows what he's talking about otherwise.

 

Thanks for the info.

Any EJ head bolts up to any EJ block. But make sure that when using a closed deck block, the coolant patterns of block, gasket and head match. Also check if the head combustion chamber matches the cylinder bore of the block you intend to use if you plan to run a head of a bigger engine on a smaller block, extreme example EJ25 block and EJ18 head.

 

Always use the head gasket that matches the block (due to cylinder bore).

 

I don't think the OP has any closed-deck EJ25s in his country. Thanks for making all of us drool, though:)

 

Jacob

I doubt anybody has a (factory) closed deck 2.5L, I was referring to the USDM Legacy 2.2 Turbo block

 

I've got quite a lot of experience building hybrid Subaru engines, mainly turbo though. I've tried all sorts of combinations and generally 2.5L heads do not work on smaller bore blocks as the diameter of the combustion chamber in the head is bigger than the diameter of the cylinder bore.

My next Frankenmotor I'm going to build is a hybrid build using JDM EJ15 cylinder heads and block (cylinder bore 85 mm) with a Phase I EJ25D crank (stroke 79 mm), displacement 1.795cc. It will be breathed on by either a small TF035 turbo (used on EUDM Forester 2L Turbo) or a TD04-13G. Custom made pistons and Pauter small big end rods. This should make for a nice torquey motor.

 

I will be running it on a JDM Version IV STI ECU, which on a 2L makes 255 lb-ft and 280 HP. On my hybrid motor I hope to get 200 lb-ft and 210 HP at 5500 rpm.

I doubt anybody has a (factory) closed deck 2.5L,

 

IIRC, EJ257 is Semi closed (bridges at top, bottom and sides)

IIRC, EJ257 is Semi closed (bridges at top, bottom and sides)

 

Yeah, that's the closest to a closed 2.5 that I know of. LeoneTurbo's advice still holds regarding making sure the coolant passages line up. I think I remember the EJ257 coolant passages being pretty different than previous blocks.

 

Jacob

http://forums.nasioc.com/forums/showthread.php?t=1107352

Has some good pics of the drilled headgasket.

Yeah, that's the closest to a closed 2.5 that I know of. LeoneTurbo's advice still holds regarding making sure the coolant passages line up. I think I remember the EJ257 coolant passages being pretty different than previous blocks.

 

Jacob

That's not just the EJ257, but all post-1999 engines (SOHC and DOHC share same gaskets/pattern) and all pre-1999 DOHC engines.

Huh - we didn't do a thing to the head gaskets with the EJ25D and EJ22E heads. They looked close enough and it's running just fine on an EA81 radiator with 1-1/4" inlet/outlet .

 

GD

I did a pretty fierce amount of research and asked some of the gurus on NABISCO before doing this. The general consensus is that you can do it either way you want. I opted to not drill partly because I didn't want to compromise the integrity of the gasket, and mostly because I didn't want to eff anything up.

 

I only know of one Frankenmotor failure, and I remember when that guy was experimenting with turbos and superchargers on that same block. This was back before the kind of advanced engine management we have nowadays.

 

Jacob

This was back before the kind of advanced engine management other people besides myself have nowadays.

 

Jacob

 

Fixed .

 

GD

Fixed .

 

GD

 

I don't get it...

 

https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxhc3ViaWVuZXdiaWV0dW5pbmdndWlkZXxneDoxMGYzM2M5NjBlYzY3ODI4

 

Jacob

Inspiring!

 

I will buy a Legacy 2.2 GX again, I miss it too much. And then it will be franken motored!

 

I love the minimalistic way of building! Most power for least money.