Frankenmotor build? Benifits?

Ok... so I did a search on this topic and could find anything..... I've got an EJ25 BD legacy that has 195k miles on it. Good motor. But I want to rebuild it and add some horse power as well. I always hear people talking about the "frankenmotor" (2.2L heads 2.5L block) but all they do is mention it. I'm curious as to what the benefits would be if I did this, add performance cams and a crank. Would it be able to handle a Turbo running about 10-12 psi? Just all the way around curious as too the pros and cons of this

Two very good reads on building subaru motors, one is for turbo and on NA

 

http://forums.nasioc.com/forums/showthread.php?t=2141800

 

http://forums.nasioc.com/forums/showthread.php?t=631527

 

If you have any questions on building motors let me know.

You can't run a turbo on it. This build increases the compression ratio to about 11:1, way too high for a turbo.

It's not enough power to need a better crank, the stock one is fine.

You will see a power gain with performance cams, probably add some area under the power curve.

Ideally you'd use the dual port exhaust heads, since they flow better.

 

The pros, I'd say. You get more power, you don't have to deal with the DOHC heads (hard to change plugs, hard to adjust valves, annoying to do timing belt)

It adds to your street cred

 

Cons that you have to run higher grade gas. you CAN run 87, but it works a lot better on 89.

Higher compression means more stress on the engine and head gaskets.

 

For the note, I have one of these builds. 2.5 block with about 240k miles. It was overheated to the point of seizure twice by the PO. I have single port exhaust heads with about 320k on them that I took off my 2.2 that seized.

It goes like stink! It's a lot of fun.

If I powerbrake I can spin all four tires when I take off on dirt roads.

And since I have a garage full of engine and transmission parts, I don't care about breaking stuff

Higher octane is a kicker for me as I want to just dd my car but I also want dual ports and get rid of my single port header on my phase 2.

Phase 2 is a whole different game...

How would one go about lowing the compression on a EJ25 so it could handle a Turbo. Is it worth it or would I be better off trying to do an EJ20 Turbo swap?

From what I have heard on flow benches is that the single port 2.2 heads flow better.

 

However they don't make a header for them. So you could make that up with the dual port heads.

 

Unless you're like me and own a rare single port header.

From what I have heard on flow benches is that the single port 2.2 heads flow better.

 

However they don't make a header for them. So you could make that up with the dual port heads.

 

Unless you're like me and own a rare single port header.

 

Really? I'd never heard that before, where did you come on that information?

 

The best way to lower the compression on an ej25 is to change the pistons to lower compression ones.

WRX or aftermarket 2.5 pistons for turbo engines.

 

The problem though, with the 2.5 block is they like to blow head gaskets.

Even so, you can't reliably crank a lot of HP out of the DOHC block. The cyl walls are thin and completely open deck. Too much power and they start to move very slightly causing head gasket failure.

So to ever Turbo an EJ25 would probably be a bad idea. Ill probably wait till the motor starts to go bad and drop a Turbo EJ20 in it. I've heard is a difficult swap but in my opinion well worth it=)

Ya, there's a reason the EJ25 turbo blocks are semi-closed deck.

Mechanically it's a pretty easy swap. Everything just bolts in.

It's a lot of wiring, but if you can keep it all organized and read a wiring diagram. It's not a huge deal.

Sweet! Cause I love my legacy. Just doesn't make as much power as I'd like and upgrades for it are expensive and just not completely worth it. An EJ20 would be AWESOME. more than enough power

to turbo a stock phase 1 block is hard. the phase one block presents a problem, small rods, and the rod journals are 48mm. most aftermarket rods are for a crank that has 52mm rod journals(phase 2). but you say hey, why not just put a phase two crank in? thats a problem

 

the phase two cranks have the trust bearing at the # five main, your block has it at the #3 along with the crank, which has 48mm rod journals. see the problem?

 

basically these phase one block are not supported by the aftermarket world. plus you got the open deck design(which is a debate in itself, iv seen people boost them above 25psi)

 

what i did is i bought a cheap(50 dollar cheap) open deck phase 2 block and am doing the following to it.

 

diy closed deck

sti rods

sti pistons

1-2 thou wall clearance

and i still need to source a phase 2 crank as the one that came in it was missing 30 thou off 2 of the journals(major rod bearing failure)

 

then youll have a block that can bring you to about 400 hp.

 

ive got a set of hydraulic heads dohc to slap on it to that im having rebuilt and ported.

What method did you use to make it closed deck?

I've seen a few different how tos on honda engines, and such. But how did you do it to a subaru block?

i have it all planned out. so far i'm pretty sure ill be the first documented person with a Subaru block doing this.

 

what im going to do is this.

 

place block halves on level table(and further level with a level on the deck surface.)

 

place all bolts into the holes of the water jacket(block half bolts, water pipe, everything but the deck)

 

pour salt or sugar(probably sugar cause aluminum hates salt, but then again sugar can clog the radiator)

 

i will fill the water jack only after i place a rod wrapped in paper above each block half block what this does is kept the close deck use able. i need to be able to fit a socket down into the water jacket to tighten the bolts for the block halves.

 

so basically now i would have a block. water jacket filled with salt/sugar with post sticking up out of the salf/sugar

 

the salt/sugar will not be to the top of the deck, but 3/8 down from the surface.

 

this space will be filled with aluminum epoxy. devcon F-2 to be exact.

 

obv before you do all this you need to prep the surfaces for the epoxy to cure to.

 

the melting point of devon is 250-350 degrees. 350 being the ideal number but as with any epoxy if you don't mix it together right the result is variable

 

but hey why am i typying this, ill be doing it next week/weekend.

That will be pretty cool if that works! Like i said, I've seen it on straight engines, but a boxer makes it WAY harder.

I'm looking forward to pictures.

 

Also, you don't have to go clear up to the top of the mating surface. If you go 1/16ths less, you don't have to worry about perfect level.

 

I have half a junk block if you want to practice... Dunno if you're anywhere near Maine though.

i came some half blocks. and i say 3/8 from the deck cause im only putting down a 5/16 inch deck.

My experience with a frankenmotor, ej25d block with ej22e heads, has been problematic. The damn thing keeps wanting to bog out like it's not getting fuel, or air, and yet both are within acceptable limits. New map, new air flow sensor, spark plugs, wires, I even seafoam the intake. It's almost like it's detecting not, but when I use the torque app and it's knock sensor plug-in, it detects nothing. Has anybody else had an issue with this?

Im also sort of curious about that. I have a spare 98 ej25 block and i was sort of wanting to put the ej22 dual exhuast port heads on it but don't want to of its a problematic thing

 

Dohcej22e knows a bit about hybrid builds as well as setnev and some more members but i havent seen them on in awhile probably due to holidays

My experience with a frankenmotor, ej25d block with ej22e heads, has been problematic. The damn thing keeps wanting to bog out like it's not getting fuel, or air, and yet both are within acceptable limits. New map, new air flow sensor, spark plugs, wires, I even seafoam the intake. It's almost like it's detecting not, but when I use the torque app and it's knock sensor plug-in, it detects nothing. Has anybody else had an issue with this?

 

Which crank gear and ECU are you using? This makes all the difference. The crank gear needs to match the heads that you're using, so you should be using the 22E crank gear on the 25D block. ECU should work no matter what, unless you're running a 99 EJ25D ECU.

Never considered the crank gear had to be changed. I knew the cam gears were sensitive, though. What's the noticeable difference between?

 

Ej22e ecu and ej25 crank gear.

Never considered the crank gear had to be changed. I knew the cam gears were sensitive, though. What's the noticeable difference between?

 

Ej22e ecu and ej25 crank gear.

 

The EJ22E camshaft is a SOHC. The snout gear is for a EJ25D which is DOHC. They are incompatible as the ECU expects a synchronized reading from one but gets the opposite.

 

The cams and crank are out of sync. In short the cam sensor is telling the ECU "I have 2 cams" and the crank sensor is telling the ECU "No, I have 4 cams". There is more teeth on the EJ25D crank snout gear. Either ECU can be used for either engine (EJ22E on an EJ25 and vise versa), but when you build a frankenmotor, you have to trick the ECU into thinking the heads are the same as the block by swapping crank gears. Its the little caveat that most people overlook and then wonder why their frankenmotor wont run right. Most of the time they think the timing is wrong and end up bending valves by trying to fix it.

 

A buddy of mine ruined 2 perfectly good engines building a frankenmotor. After he killed the second one I asked him what went wrong. He said the timing was never right because the engine acted like it had zero power. I asked him if he matched the crank gear to the heads. Needless to say, his 2nd gen shell is now mine and sitting in my garage waiting for me to finish my frankenmotor I'm building.

Hey setnev what kind of Frankenmotor are you building? Is it a ej25d bottom end or the ej22e bottom end? I feel like the 25 bottom ends are more uncommon

Would this situation still be plausible if this build has 5000> miles on it and this running issue seems to only happen if i go harder on the engine?

The EJ22E camshaft is a SOHC. The snout gear is for a EJ25D which is DOHC. They are incompatible as the ECU expects a synchronized reading from one but gets the opposite.

 

The cams and crank are out of sync. In short the cam sensor is telling the ECU "I have 2 cams" and the crank sensor is telling the ECU "No, I have 4 cams". There is more teeth on the EJ25D crank snout gear. Either ECU can be used for either engine (EJ22E on an EJ25 and vise versa), but when you build a frankenmotor, you have to trick the ECU into thinking the heads are the same as the block by swapping crank gears. Its the little caveat that most people overlook and then wonder why their frankenmotor wont run right. Most of the time they think the timing is wrong and end up bending valves by trying to fix it.

 

A buddy of mine ruined 2 perfectly good engines building a frankenmotor. After he killed the second one I asked him what went wrong. He said the timing was never right because the engine acted like it had zero power. I asked him if he matched the crank gear to the heads. Needless to say, his 2nd gen shell is now mine and sitting in my garage waiting for me to finish my frankenmotor I'm building.

 

Odd. I'm running Phase II EJ25 SOHC heads on an EJ25D core in a car that was originally EJ22, and it's running great. I don't remember changing the crank gear, got over 1000mi on the engine, though I originally ran it in an EJ25D car, got it running yesterday in the EJ22 car. Only issue I had was that I had to grab some 95 model crank and cam sensors, couldn't get it to start until I did that, but it runs strong.

 

edit: Actually, I also ran it on an EJ22 ECU for a short time in the EJ25 car, it ran even better there than with the EJ25 ECU.

Hey setnev what kind of Frankenmotor are you building? Is it a ej25d bottom end or the ej22e bottom end? I feel like the 25 bottom ends are more uncommon

 

I am going even more uncommon. I am going with a 99 EJ223 bottom end (Phase 2) and 99 EJ25D heads. It is possible to go the other way around but that usually lowers the compression making it ideal for boost.

 

Odd. I'm running Phase II EJ25 SOHC heads on an EJ25D core in a car that was originally EJ22, and it's running great. I don't remember changing the crank gear, got over 1000mi on the engine, though I originally ran it in an EJ25D car, got it running yesterday in the EJ22 car. Only issue I had was that I had to grab some 95 model crank and cam sensors, couldn't get it to start until I did that, but it runs strong.

 

edit: Actually, I also ran it on an EJ22 ECU for a short time in the EJ25 car, it ran even better there than with the EJ25 ECU.

 

The combination of the block and the heads make up whether or not it needs to be changed. Subaru was weird with parts in the 90's, so it is entirely possible to never swap a crank pulley and it work with no issues.