Ej251 with ej22t heads questions

[Imprezafan93]

Hey guys so i recently got a legacy ss and was enjoying it for all of about a week before i pulled the shortblock to sell to another user in need..everything is for sale for the right price, im not picky. So that leaves me in a funny situation

I recently helped a buddy swap over an engine after his headgaskets failed, he decided he didnt want to risk it again and purchased a replacement motor. He paid me for my time and i asked if i could hold onto the suspected 'bad' motor, an ej251 from a 2003 outback

Ive inspected the block and i will just do a resurface, cylinder walls look good and everything else looks great. I plan on running the vf11, or maybe a td04 but no more than 8 psi

So now im owft with an ej25 short block, two sets of ej25 sohc heads, and a set of ej22t sohc heads. I know i could boost the ej25 with ej25 heads but i have issues with that because
1)not into customizing everything to support a turbo
2)intake manifold including all sensors and everything wont mount on 251 heads even if they do flow better im looking at a bunch of mods to make the intake mani from a newer phase 2 work.

Anyone have an idea what compression numbers i would be looking at with ej25 block/ej22t heads?

I have head gaskets for an ej251, they look almost identical to 22t gaskets, just a touch different, think id be good to run them or should i get thick head gaskets to try to lower compression and keep it non interference?

i know everyomr will flame me for wanting to put an inferior bottom end into the car but its cost effective and i already daily drive a forester so its more for weekends/occasional autocross. Ive read of people doing ej22/25 hybrid n/a buids with the higher compression it adds more low end torque..

I dont care about blowing the bottom end and i have all the parts to assemble and drop it in next week, just have been researching and trying to gather info before i move forward.

Im not into this car very much money now..~100 dollars including purchase price and i have all these parts ready to go in. Very anxious/excited/nervous lol. This will be experiemental i think because there isnt much info on the topic of an ej25/22t hybrid

Any thoughts, ideas, insight?

Is there any interest/curiosity? Ie, does anyone just want me to post a build journal and info just because they think its interesting?

Let me know if you guys want to see it done and let me know if theres a better combo or why i should absolutely not do it (i may likely do it anyway though to be honest, because i like doing swaps and i domt know what will happen, and i bet other dont know either)

[86BRATMAN]

You'll be making a near 11:1 compression engine with the ej251 and 22t heads. Not good for boost by any stretch of the imagination.

[Imprezafan93]

Where are you getting the 11:1 compression ratio? Curious not questioning, i read anywhere from 10:1 to 11:oops:1 but i was also reading of many guys who have boosted a 25/22 hybrid and had good results. Wouldnt a higher octane and good engine management take precedence over compression ratio?

I dont see any issue with boosting a car with that high of compression othee than the risk of ruining a bottom end due to poor engine management..if you have facts and/or real information do share, like i said i read a couple different builds of boosted 25/22 hybrid motors, one guy mentioned hes been running a full bar for 58k miles

[Alphius]

You may not mean it like this, but it sounds like you're looking for an answer you won't get from us. You've decided you're going to do it and looking for confirmation that it'll work out fine. It won't.

10.6:1 CR plus or minus a bit according to the calculations I ran. Definitely incredibly detonation prone even with good tuning. You'll be compression limited to a very low boost level. Your post said nothing about engine management, and it will definitely blow up right quick on a factory tune. Octane and tuning cannot compensate for an engine that is unsuited to boost. You would have to pull so much timing to avoid detonation that your EGTs would be sky high and it wouldn't make much power. It would have plenty of off-boost torque though.

Will you be running E85 and an aftermarket standalone ECU? That's pretty much your only chance for avoiding failure and making any decent power.

If you're only in the car $100 and you don't care about potentially ruining the engine, go right ahead and you'll find out that we're right. 86BRATMAN and myself have been around the block a few times and both of us have built and tuned some very unique combinations.

Your only chance at making it work would be to drop in a set of EJ257 STI rods and pistons for around a 9.6:1 CR. You'll still need aftermarket engine management, but at least this combo would have a reasonable chance at making some power without detonation or incredibly high EGT.

[86BRATMAN]

The ej25 ej22 hybrids people turbo are configured the other way. It's an ej22 shortblock with ej25 heads. The ej25 heads have a larger combustion chamber volume than the ej22, with the exception of the 99-01 ej221/2/3, thus it lowers the compression ratio to a more turbo safe number. The closest combination to what your are talking about is usually call the high compression frankenmotor, and is useful for making good low end torque. Even without adding boost to the mix they are detonation prone on factory ecus.

[wtdash]

.... 86BRATMAN and myself have been around the block a few times and both of us have built and tuned some very unique combinations.

I'm seeing a Pun here....no?


Can the OP put some plain old EJ22e heads on there to make it more 'manageable'? It would probably be as quick as the EJ22T?

[Imprezafan93]

Motor is fully assembled, took a tiny bit of modificationg but nothing crazy..everyone should know by now how directly compatible subarus are. MY logic is that ive read of many people who have turboed both ej22's and ej25's with low boost and little to no engine management. Plan is go with a wrx or walbro fuel pump, i have a wrx pump laying in a box with 440 cc injectors but im not sure atm if theyll be necessary. May also go with a mbc to turn boost down low and take it from there, not as if the vf11 makes enormous power to begin with. I have to fab up my 06 intercooler but dont feel like screwing with it right now, we'll see how the frankenmotor handles itself on first start up-

it may all be a wash but like i said im into it about 100 bucks now including car purchase price and full drivetrain so kinda experimenting for giggles, kinda curious, and hoping i can have some fun come snowfall.

ALOT of factory fi engines run over 9:1 compression and are turboed, albeit in moderation, but i dont forsee major issues. Ill run highesy octane pump gas i can find and if not i may supplement with meth or something, havent read too much into methanol but if im not mistsken it can help with detonation?? I dont have experience with it so maybe someone else does?

If it blows it blows, no biggie i do all the labor anyways for funsies, and i may be able to get my hands on a wrx short block on monday for 50 bucks, he has an offer for 100 from someone who is supposed to pick up this weekend but (im also the guy who offered 100 on a differnt phone)..so we'll see

Anyone whos interesred can check out my youtube vid once its dropped in tomorrow im gonna post up a first startup and drive granted it gets that far, and explain what i did.

No need for people to get upset and pretentious im havin some fun, relax guys this is what subarus and life in general is all about, hypothesis and experimentation, wish me luck and ill post results hopefully (or ill be too embarrassed and delete my account) lol

[Imprezafan93]

The ej25 ej22 hybrids people turbo are configured the other way. It's an ej22 shortblock with ej25 heads. The ej25 heads have a larger combustion chamber volume than the ej22, with the exception of the 99-01 ej221/2/3, thus it lowers the compression ratio to a more turbo safe number. The closest combination to what your are talking about is usually call the high compression frankenmotor, and is useful for making good low end torque. Even without adding boost to the mix they are detonation prone on factory ecus.

Im aware my swap is rather...backwards.. but i had everything laying around, if it doesnt work ill try something else, but as of now all im invested is a little bit of time

[Imprezafan93]

Started her up first time today, fired right up and running good, i brought it down the road and back, stil have little odds and ends to tie up but taking a break from the car for a few days. ILl post a youtube link when i get around to uploading a video. I dont plan to boost any higher than 8 psi, upgrading to a tdo4 boost controller and fuel pump next time i work on it, along with going back to the old style tensioner as this one is bouncing up and down, i guess thats what happens when they sit uncompressed for a couple months, who'da thought., as f now its running good and torque/powerband feel smooth, havent flogged it though maybe when the snow hits, stay tuned for updates

[Imprezafan93]

Hey guys im back! Bad news, the shortblock i installed has several issues, a couple of which im at fault for:

The ej251 with ej22t heads combo did not pan out. As it happens, the block sounds like it has a bearing issue and starting knocking lightly, but a knocks a knock..i also had to drill the headgaskets as well to make them work with the 22t heads which i wasnt all that stoked on in the first place, long story short, head gasket is roached, short block is knocking, maybe the super high compression is somewhat to blame ss well but i think it was a combo of half assedness parts and human error. So my question to the gurus:

I have a couple different routes and im looking for input

Goals-
Cost effective
Modest power numbers and driveability maybe 220 or 250 crank hp nothing really insane

Parts i currently have in my possession
2-ej205 short blocks recently acquired
1-set of ej205 heads
1-rebuild ready ej251 shortblock
1-sti crankshaft
1-set of 4 sti pistons-no rods.. (yet?)
1-06 wrx intercooler

Different possibilities: need help deciding and wisdom

1.Rebuild ej251 with sti crank rods and pistons, again running ej22t heads:
I believe i also have to change the thrust location if im not mistaken, how does that work?
Id also have to probably pin the block to feel more secure

2. Drop in ej205 with ej22t heads
Is it necessary to go forged pistons with my meager power goals?
Will the ej205 head gasket work, and will i have to worry lots about interference going mls?

Go full swap and pickup a wrx intake manifold, harness, ecu and make it a full on winter project:
This option would take me much more time and $$ but are the other two options unrealistic or not

Thanks in advance, just trying to put together a runner for some time until schools over and i can afford a newer wrx again. Trying to be cost effective but not sloppy

[Alphius]

If you had used 257 head gaskets you wouldn't have had to drill them out.
Likely that the 251 was fine and the high CR plus boost toasted a rod bearing.

EJ251 with STI internals does not require thrust bearing work. They're both Phase 2 so have the same thrust bearing location. That was an option I suggested earlier if you'll go a little bit back in the thread. Still needs engine management of some sort to prevent breakage. Forget pinning the block, EJ205 is open deck and holds 450whp easy without splitting sleeves or walking. 251 is nearly as strong. I ran 19psi on an open deck EJ22 with no problems at all.

205 with 22T heads is fine, no interference and you can use standard 205 head gaskets. Super low CR so should be pretty reliable, but off-boost torque suffers from the displacement drop and low CR.

You might see 220 crank HP on a factory 22t turbo ECU, but with an N/A ECU and no engine management at all it won't happen. RobTune ECU will get you to that 250-280 crank HP level, but you have to keep the CR low enough to not detonate, so like 8.5:1 max. ESL is another option for tuning, and you can tune it yourself if you're confident enough to run a higher CR without detonating.

Long story short: If you do ECU work, run the 251 with STI internals. If you don't, run the 205 and keep CR low. N/A ECU can do around 7-9psi fairly reliably with a RRFPR and no other mods. 22t ECU might get you to 12-14psi reliably enough. RobTune gets you to the 250+ whp level at 17-18psi as long as the CR is low enough. ESL ECU gets you whatever you want to run as long as you can tune.

[Imprezafan93]

[first of all id like to say, thank you for the informstive response!

I apologize if i seemed bullheaded and apprehebsive towards advice at first, and i was. Ive since educated myself a tad more, you just keep learning and thats where the fun is right?

If i didnt mention it up top i better now, im running a full turbo legacy ss harness, i swapped everything from the donor car, not running an n/a ecu or harness, all turbo. So at the very least i have that for engine management, id like to do a robtune or standalone for practicality purposes but not in the budget until january or february if i decide to go that route.

So an sti crank/pistons will drop into the 251, thats good news, should i look for oem ej257 rods? I have s set of 205 rods sitting around but im not sure if they sre compatible because i am not aware if the stroke is different.

Ive read that open deck does well enough, so with my modest goals i suppose ill be good as you mentioned

Wouldnt a ej251 with 57 internals still have a high CR? How much do the pistons lower compression if anybody knows?

I think im going to start disassembly of the block next week while i have time, maybe ill actuslly take photos this time for anyone who is interested.

Im looking at the 205 head gaskrt-looks like s victor reinz, this too does not have the hole for the coolsnt passage at the 12 o clock position on the ej22t heads so im going to have to drill again or cover it? I dont feel comfortable about either of those options.

I talked to another member who said he did this setup and used ej22t head gaskets and ran it for a year before selling with no adverse effects, do i risk compromising the fire ring??hmm

Thanks for the knowledge guys, its getting there, as of now im into this car -50$, i actually made a few bucks selling off the n/a legacy parts, so i can start sinking some money into the right Avenues

[Alphius]

It's always good to keep learning, I learn new things every day. Sometimes you just have to try stuff for yourself and learn through experience.

257 pistons require 257 rods. The 257 rods have a taper at the top to fit into the piston skirt. 205 rods are also the wrong length, but they won't fit into the piston properly anyway.

257 pistons and rods with 22t heads makes around 9.6:1 CR, still too high for a 22t ECU's timing levels but much better than 251 pistons. 257 pistons are extremely detonation sensitive, so I wouldn't be surprised if you broke a ringland before toasting a rod bearing this time.

I wouldn't mismatch bore size on HGs. I'm not familiar with 22t heads on anything but a 22t block, all my modified turbo Subarus have been DOHC, the only firstgen turbo cars I've built have had stock block/heads. Speaking of that, why not go DOHC with a cheap set of 97-99 25D heads and intake manifold? That'd drop your CR to safe levels and enable you to use ej257 MLS headgaskets which should match the coolant ports on the heads better.

[Imprezafan93]

^i remember reading about how the rod is specific to piston oem wise on wrx vs sti, idk why i had a brain fart on that.

I have ej205 heads but i dont know what would be necessary to make that work with the 22t ecu, id be essentially doing a motor swap in which it might make more sense to go obd2 and swap a harness and ecu in, which im not really trying to do at thia point, i want to daily this thing for a little bit.

I think the 205 block with 22t heads sounds likr a decent combo, low CR but still, i just dont know how id go about the head gasket. I thimk im gonna build up a hybrid while im driving this thing with the 251 and 205 heads, and in that time i can buy a harness and ecu to go full obd2 proper, idk about putting 205 heads in with the 22t ecu