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This is out of curiosity and not necessity, but came up in conversation and I am not sure of the answer.

 

I know that the phase one frankenmotor of 90-98 EJ22 heads on a 2.5 block make a high compression, higher HP motor.

 

Does the same hold true for using the 99+ Ej22 heads on a 2.5 block? I have been under the impression that the phase 2s were similar enough that it would run fine, but not create a much more powerful motor. (certainly not enough to surpass a phase 2 EJ25) But that's just what I've heard.

 

Anyone have more info? Or first hand knowledge of hp increase/decrease?

Edited by AdventureSubaru

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For phase II the heads are basically the same heads, so I don't think they'd have any improvement and probably worse since you'd reduce exhaust flow from dual port to single port. Valves are even the same part number between the two.

Edited by idosubaru

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Complete waste of time and money for zero gain. Get some delta cams if you want more power out of the phase 2 engine.

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That's what I figured but can never tell on facebook. Been kicking around this forum for enough years that i know who knows their stuff and who doesn't.

 

One guy was insistant that the phase II setup of 2.2 heads on 2.5 block was superior to the phase 1 setup. Didn't make sense to me but wasn't in a place to argue as my experience in phase 2s is limited to engine swaps alone where I know phase 1 pretty well by now after a few dozen cars and motors and whatnot.

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Maybe they were thinking of using the 22e heads on a 251/3 shortblock, which is marginally better than using a 25d shortblock. I almost want to seak out that post and snap some pics of the 251 and 222 heads I have just for proof lol.

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Having examined both heads side by side I can tell you they have the same basic chamber size. The only way to tell them apart is by the exhaust port design. There is no compression gain, therefore no real performance from using them. You get an oddball exhaust header port - that's about it.

 

GD

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Maybe they were thinking of using the 22e heads on a 251/3 shortblock, which is marginally better than using a 25d shortblock. I almost want to seak out that post and snap some pics of the 251 and 222 heads I have just for proof lol.

This will yield an unsuitably high compression ratio. Somewhere in the 11.5 range. It's actually pretty close to using 96 25D pistons which yields a compression so high it will melt pistons - over 12 IIRC. Don't do it.

 

The acceptable combinations are:

 

22E heads with 97 to 99 25D pistons using 25D thick head gaskets. About 10.6:1

 

25D heads using 99 to 04 251 pistons, and '06+ STI head gaskets. About 10.2:1

 

Both run quite well on premium.

 

I know of no other combinations that do not require custom pistons and head gaskets, etc.

 

GD

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It is outside the "safe" range of compression for pump gas on a stock tune. But then again the dohc ej22e with a td04 slapped running 6psi on it has an effective compression ratio of 12.4:1.

 

 

I also think you mean 04-06 sti gaskets, the 07+ have the redesigned coolant passages and no longer match the older heads.

  • Like 1

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This is interesting.  Is there any database that might show different combinations that work/won't work?

I think the engine I have is the 2.5 dohc phase 2...... 

I would like to subscribe to see what I can do, since I assume I will have to eventually tear it down for a head gasket repair.  We all know that upgrades need to be installed at that time.

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All DOHC NA EJ25s are Phase I electronically speaking.

 

99 DOHCs for practical purposes are Phase I. They are Phase 1 heads, intake manifold, ECU, wiring, etc bolted to a Phase II block I think is the accurate way to say it.

 

The 99 DOHC is plug and play interchangeable with 96-98 Phase I's but not 99+ Phase II's.

 

So in most common ways it's easier to think of them as Phase I.

Edited by idosubaru

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I don't know of any databases. You can download some excel calculators that calculate a few metrics based on various blocks, heads and gaskets. Keep in mind resurfacing is going to change things too if you're trying to be that precise.

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Not all na dohc ej25s are phase 1, parts of the world got the ej254. Which is phase 2 single avcs high compression.

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Not all na dohc ej25s are phase 1, parts of the world got the ej254. Which is phase 2 single avcs high compression.

international markets?

My phone isn't showing right now but I thought OP was stateside, maybe I missed that.

 

But yeah copy, there are tons of EJ flavorings and offerings globally. an EJ15 would be fun to see.

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I'd like to get my hands on an ej154 lol. It's not uncommon to see a ej254 for sale when looking at replacement engines online. A local importer has 5 of them sitting on their shelves because they thought they'd be a drop in replacement for the 25d and brought them over.

Edited by 86BRATMAN

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I might take an EJ15 too! Although the EJ18 legacy swap was too gutless in the mountains (got 32 mpg in an automatic in flatland but only like 22 around here) maybe I could use it in a lighter EA/ER. Yep I've seen the non US market engines when I buy JDMs.

Edited by idosubaru

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All DOHC NA EJ25s are Phase I electronically speaking.

 

99 DOHCs for practical purposes are Phase I. They are Phase 1 heads, intake manifold, ECU, wiring, etc bolted to a Phase II block I think is the accurate way to say it.

 

The 99 DOHC is plug and play interchangeable with 96-98 Phase I's but not 99+ Phase II's.

 

So in most common ways it's easier to think of them as Phase I.

 

So then a 99 would be an upgrade for 96-98 owners perhaps?

 

Most notably I'm thinking the #5 thrust and larger 52mm rod journals vs. the 96-98 48mm. 

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So then a 99 would be an upgrade for 96-98 owners perhaps?

 

Most notably I'm thinking the #5 thrust and larger 52mm rod journals vs. the 96-98 48mm.

It's not that big of a deal in practice. I haven't seen a major difference in rod bearing longevity between 48 and 52. And the only thrust bearing issues I've seen were on 22 and 22T engines.... The #5 thrust does seem to be more reliable but thrust bearing failure on the #3 engines isn't common by any means.

 

The best upgrade is to just put the D heads on the 251 bottom end using 770 head gaskets.

 

GD

Edited by GeneralDisorder

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Or you could be smart and use the 11044AA642 gasket that actually matches the coolant ports of the 25d head.

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Or you could be smart and use the 11044AA642 gasket that actually matches the coolant ports of the 25d head.

It makes zero difference in the end result what gasket you use. The ports don't match in other areas on those gaskets. Subaru has used lots of mismatched gasket/head combos in stock configurations.

 

We use the 770 gasket on everything. Including 205 heads on 257's making 400 AWHP. In no circumstance has the coolant flow across the gasket interface been any concern whatsoever.

 

GD

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It's not that big of a deal in practice. I haven't seen a major difference in rod bearing longevity between 48 and 52. And the only thrust bearing issues I've seen were on 22 and 22T engines.... The #5 thrust does seem to be more reliable but thrust bearing failure on the #3 engines isn't common by any means.

 

The best upgrade is to just put the D heads on the 251 bottom end using 770 head gaskets.

 

GD

 

I have personally seen a greater # of 25D rod failures vs. 2.2 or 251/3 and later

 

Although it's mostly a matter of how often the oil was changed.

 

770? a Subaru #?  or is that Cometic or something?

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I am going to bump this, as I have a few questions.

 

I got a good EJ253 (1 blown HG, <100k miles) for free as I am planning on building a frankenmotor. I currently have 96 EJ22 heads (single port exhaust) on my 96 EJ swap in my Brat.

 

I was going to use the EJ22 head bolts, and Cometic  H1631SPK051 hybrid gaskets with the 253. Is this a good combo, or should I use another gasket like the Subaru 11011AA770 standard EJ gasket?

 

I will also be getting Delta Cams torque grind.

 

Thanks for the tips

Edited by iluvdrt

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Compression is much too high with a 251/3 bottom end using 2.2 heads. It's over 11 even with 25D gaskets and it will detonate like crazy due to high static compression and terrible quench. There is not a gasket that will fix the problem. The thicker you go the worse the quench becomes and makes the performance aspect of the build useless.

 

Best combo for performance is going to be a 257 bottom end (pistons and rods anyway), 97-99 25D heads milled .040", and 770 gaskets. 10:1, proper quench, and dual cam heads.

 

GD

Edited by GeneralDisorder

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Ive been doing some reading on 2.5RS and a few other forums and they have decent luck with this set up. weird.

 

Ill try it any ways. Worse case, I'm only out $100 in gaskets, and Ill put my 22 back together.

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Here is what I came up with for a EJ 235 with P1 EJ22E heads. This should work.

 

253 Bore 3.92"

253 Stroke 3.11"

22 Cyl Head volume 41cc

253 Effective 253 dome volume -12.2CC

253 Deck clearance 0.16"

Compressed gasket (cometic h1631spk051s) 0.030"

253 number of cyl 4

 

Compression ratio 10.26:1

total displacement 150.14 in/3

Total displacement 2461.31cc

 

So 10.26:1 is pretty good and certainly not within melting the pistons threshold. A stock EJ 253 is 10.1:1 compression so this is just a tad bit bigger bump with a bit more restrictive head that the 253 came with. Should be good for about 170-180 CHP or there a bouts.

 

I have read on numerous other forums that this engine requires about 30* of timing to run well on at least 91 octane. The EJ22E ECU from what I can tell can pull as much as 34*, so this combo should work out fine.

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