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Old 12-25-2003, 09:36 PM   #1
Soon2BturbodRS
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Default EJ22 vs. EJ25

Which engine, the SOHC EJ22 (NA, not turbo leg) or the SOHC EJ25 (2.5RS phase 2) will respond better to turbocharging? Which is a better bet with higher miles? See, I can either turbo my car ('99 OBS), or buy an RS and turbo that...

The EJ22 has lower compression, thicker cylinder walls (iirc)... umm... That's about all that it has over the EJ25 that I can think of. EJ25 has displacement (to a positive and negative affect, more positive) and better flowing heads...

Which engine, in theory or in your own experience, will be more reliable with high mileage (80k+), "cheap" engine management (s-afc, s-itc, rrfpr), and some pretty good tuning?

Thanks, I'm still trying to figure out whether to do an OBS-T or an RS-T...
-Ben
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Old 12-25-2003, 10:16 PM   #2
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<-- you know my bias. Im not sure that there is any proven facts. But it seems like you know all the info you need to.

Money wise, you already got a 2.2 block. I can't see it worth buying an ej25 block and going through all that work.

Money and time would be better spent elsewhere.

-Jake
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Old 12-26-2003, 12:05 AM   #3
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Yeah, I'm trying to decide whether to keep my 2.2L wagon and turbocharge it or buy a modded RS and turbo that... Decisions decisions...

Thanks
-Ben
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Old 12-26-2003, 02:28 AM   #4
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its all about bang for the buck. neither engine is gonna be ALOT more reliable and more powerful.

One scenario, you have more displacement and thus less boost, the other, you less displacement and so it can hold a bit more boost.

do what is cheaper for you.

-Jake
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Old 12-26-2003, 03:01 PM   #5
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I'd say stick w/ the 2.2L. It's got a lower CR and possibly thicker cylinder walls, as stated earlier. It's also a semi-closed deck so it can theoretically hold more boost before cylinder wall deflection. The 2.2 is a proven success story when it comes to turbos. The 2.5 is a little riskier but sometimes worth the torque curve.
If I were you I'd keep the OBS. besides an OBS-T would be a killer sleeper! "No Officer i didn't know that my waggon could do 125! really!
Dan
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Old 12-26-2003, 09:24 PM   #6
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Quote:
Originally posted by Merdock777


It's got a lower CR and possibly thicker cylinder walls, as stated earlier. It's also a semi-closed deck so it can theoretically hold more boost before cylinder wall deflection. The 2.2 is a proven success story when it comes to turbos. Dan
I think the CR is the same in some years, if its not, its only minutely different.

I was not aware it was semi-closed???

As far as proven success. I love the engine, but i dont know how 'proven it is.'

Turbocharging is always a risk. While we try to calculate the risk, it is still a risk. As long as you understand that, you wont be disappointed.

-Jake
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Old 12-26-2003, 11:03 PM   #7
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I think he means the EJ22T is semi-closed (or is it fully closed, idk)...

Right now, tho, my car has some minor problems so I need to fix some things.

-Ben
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Old 12-26-2003, 11:30 PM   #8
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the ej22t is fully closed, and i believe the only ej engine like that.

the 2004 sti engine is semi-closed

all other's are open, afaik

Quote:
Originally posted by Merdock777
"No Officer i didn't know that my waggon could do 125! really!
Dan
I'm pretty sure his car can already do 125, I went past 125ish and still had some left (ran out of space on the road)

To answer the original question, I'd say stick with the ej22, It really isn't all that worth it to buy a differeny engine that is still n/a
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Old 12-26-2003, 11:32 PM   #9
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I think ej22tt is fully closed. IIRC, only the ej20 is the semi-closed one.

I dont know how much of a difference it really makes wall-wise. Lots of honda guys are running lots of boost open deck.

I think the real deal is the head gasket not making good contact from being open-deck. o-ringed heads solves that problem.

As far as problems goes... start another thread, and let us know. I will try to help.

-Jake
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Old 12-26-2003, 11:38 PM   #10
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Here's a link to my current #1 priority... fixing the 1st/2nd/3rd gear hesitation/lagginess/disease

And regarding Honda guys... don't even get me started or I won't stop...

I'm sorta mad at myself for this but... I'm contemplating a different project car

-Ben
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Old 12-27-2003, 12:59 AM   #11
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What car are you thinking about?
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Old 12-27-2003, 01:08 AM   #12
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I would go with the RS for the sake of the better flowing heads and then do a block swap....up to you
Take it easy, Micah
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Old 12-27-2003, 01:38 AM   #13
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Quote:
Originally posted by THAWA
What car are you thinking about?
Ah, there's a few...
Impreza L, EJ22T/EJ25 hybrid, turbo
S13 or S14 Silvia, sr20 and the works
Honda Accord with an H22 (prelude vtec engine) and turbo
MR2-turbo
Audi A4 1.8T
The list goes on...

For now, I'm thinking of buying a new EJ22 or EJ22T block (whichever I can get ahold of) and rebuilding it while concentrating on suspension and braking mods... then, when my current engine decides it doesn't want to live anymore, I'll swap in the rebuilt EJ22, turbo it, go nuts, get lots of speeding tickets, and maybe die... but not on purpose.

-Ben
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Old 12-27-2003, 02:51 AM   #14
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Quote:
Originally posted by Unsung Boxer
its all about bang for the buck. neither engine is gonna be ALOT more reliable and more powerful.

One scenario, you have more displacement and thus less boost, the other, you less displacement and so it can hold a bit more boost.


-Jake
i dont think that is correct, the displacement isnt going to determine how much boost can be run safely, its gonna be the compression ratio that determines that, and you stated yourself that they are the same as the 2.5l so therefore you would still only be able to run the same amount safely.

i am pretty sure on this but not 100%, its all about CR, not displacement for boost level safety.

Ben
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Old 12-27-2003, 02:54 AM   #15
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Displacement does affect how much boost a certain turbo can produce while staying efficient and not becoming just a hairdryer... For example, a small T3 may be good for 8-9psi on an EJ25 before it is out of its efficiency range... But on a smaller EJ22, it may be able to run 11-13psi. So, it can run more boost, but it may not necessarily be more power/torque.

-ben
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Old 12-27-2003, 03:28 AM   #16
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good call, didnt think of that

Ben
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Old 12-27-2003, 04:14 AM   #17
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Quote:
Originally posted by Soon2BturbodRS
Ah, there's a few...
Impreza L, EJ22T/EJ25 hybrid, turbo
S13 or S14 Silvia, sr20 and the works
Honda Accord with an H22 (prelude vtec engine) and turbo
MR2-turbo
Audi A4 1.8T
The list goes on...

For now, I'm thinking of buying a new EJ22 or EJ22T block (whichever I can get ahold of) and rebuilding it while concentrating on suspension and braking mods... then, when my current engine decides it doesn't want to live anymore, I'll swap in the rebuilt EJ22, turbo it, go nuts, get lots of speeding tickets, and maybe die... but not on purpose.

-Ben
Good plan but you forgot the most important one, a BC/BF turbo, I'd say just buy the whole car, and make it a total sleeper, esp good with the touring wagon. PLus you get the added benefit of coming on over to legacycentral and having fun
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Old 12-27-2003, 04:58 AM   #18
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Quote:
Originally posted by PHATsuby
i dont think that is correct, the displacement isnt going to determine how much boost can be run safely, its gonna be the compression ratio that determines that, and you stated yourself that they are the same as the 2.5l so therefore you would still only be able to run the same amount safely.

i am pretty sure on this but not 100%, its all about CR, not displacement for boost level safety.

Ben
CR determines absolute boost: What i was saying, (CR being equal), most vehicles are not capable of achieving absolute boost, due to a number of variables that i am not going into. But lets say you could achieve 75-90% absolute boost on each engine (within reason).

The EJ22 and EJ25 are the same block, one has thinner cyl walls to make more displacement. So lets say that cylinder wall thickness becomes the weakest link:


THUS- Theoretically,

1. The ej22 will hold more boost but has less displacement

2. The ej25 will hold less boost but has more displacement.


Questions:

A. How much more boost can an engine safely run by having a thicker CYL wall of (EJ25-EJ22=X)

B. What percentage of power is gained by having .3L in an EJ2X Engine

C. What has potential of making more power @ the same risk factor?


If you can follow that...you can see where math becomes too complicated, and opinion takes over.

-Jake

Last edited by Unsung Boxer; 12-27-2003 at 05:12 AM.
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Old 12-27-2003, 05:15 AM   #19
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interesting, i didnt know they just bored out the same block so we have thinner walls to make the extra .3L, that sucks.

however, dont you think that the cylinder walls in both would prob hold up under pretty high boost anyways(or at least higher than the breaking point of the piston/rods)? i would think that the main factor to be concerned about would be rods and pistons, i would think though would go before a wall would blow out, but as i have shown already i dont know a thing

Ben
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Old 12-27-2003, 05:30 AM   #20
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Yeah, that brings in another thing... The EJ25 has a large rod length:bore ratio... this causes more stress on the rods over time than the EJ22...

-ben
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Old 12-27-2003, 06:31 AM   #21
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sorry for bein a noob, what what is the block on these subaru motors made of? aluminum or cast iron? i *think* that a cast iron block would hold boost better? but someone let me know if im wrong on that.

Oh.. and if you've got any questions on MR2 Turbo's, let me know..
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Old 12-27-2003, 02:10 PM   #22
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they're made from alu, but if you like the heads of an ej25 why not just put those heads on your ej22. It'll lower the comp ratio a little bit, which will help a lil with boost. meant to say that earlier but forgot.
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Old 12-27-2003, 02:40 PM   #23
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Quote:
Originally posted by THAWA
they're made from alu, but if you like the heads of an ej25 why not just put those heads on your ej22. It'll lower the comp ratio a little bit, which will help a lil with boost. meant to say that earlier but forgot.
not enough to make much of a difference. The RS heads are primarily used for their higher flow design.

I dont recommend counting on headgasket or head thickness as a primary means of lowering CR.

-Jake
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Old 12-27-2003, 04:55 PM   #24
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Quote:
Originally posted by THAWA
the ej22t is fully closed, and i believe the only ej engine like that.

the 2004 sti engine is semi-closed

all other's are open, afaik

I'm pretty sure his car can already do 125, I went past 125ish and still had some left (ran out of space on the road)

To answer the original question, I'd say stick with the ej22, It really isn't all that worth it to buy a differeny engine that is still n/a
Thawa is totally right here.

Your theories on block thickness still lack alot of internal details. Assuming that a stock EJ22 can hold more boost than a EJ25 is more dependant on compression ratio than on bottom end design. Plus, this doesnt take intercooling or tuning into play which means the difference between putting out alot of reliable power or simply blowing a motor on half the boost.

Both the EJ22 and EJ25 motors are open deck, both have similar bottom ends and pistons (minus the compression difference which is probably due to head gasket thickness), both have crappy pistons and weak cylinder walls (relatively) for boost, etc.

I would personally get an aftermarket turbo kit on the 2.2 and wait for the thing to explode...then get an EJ257 (sti shortblock) for $1400 and bolt it up to your stock heads. You could probably tune this with a piggyback if needed.

This way your dont have to do any ECU swaps, have a newer than factory block for emissions, and have a MUCH stronger bottom end for boost. The gains from head porting can be dealt with later but unless your running high boost I would just leave them be. As for cams, many turbo guys wont touch them.

Be greatful that the Subaru motors are so interchangable. Eventually your 2.2 is going to die anyways, with the STi shortblock you can save all of your OEM and aftermarket parts and simply bolt them up (however, the exhaust manifold and exhaust system might need a bit of work).

The EJ22t (I think model number is EJ22k) out of the early legacy's is a serious beast and puts the EJ257 to shame regarding an ultra-high boost capable block (even though the STi pistons are probably higher quality than stock legacy), but it wont pass emissions to save its life if you put it in a modern impreza chassis.
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Old 12-27-2003, 06:09 PM   #25
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Quote:
Originally posted by Snagtastic
Thawa is totally right here.
Yep... The thicker head gasket will lower the compression ratio because it increases the area of the cylinder, therefore the ratio is lowered

Quote:

Your theories on block thickness still lack alot of internal details. Assuming that a stock EJ22 can hold more boost than a EJ25 is more dependant on compression ratio than on bottom end design. Plus, this doesnt take intercooling or tuning into play which means the difference between putting out alot of reliable power or simply blowing a motor on half the boost.

With as many variables kept constant - as possible - between the two engines (same intercooler with the same pressure drop, same turbo & setup, etc), the EJ22 can pump out more boost, bottom line. This doesn't mean that you can make more power on an EJ22 than you could on an EJ25... A lot of other variables like valvetrain, displacement, and what-not increase the power capabilities of the RS engine. ie: I've seen a few EJ18s pumping out in excess of 15psi, but they are probably about as equal as an EJ25 at 5-6psi, power-wise.

Quote:

(minus the compression difference which is probably due to head gasket thickness)

Wouldn't you think that Subaru would have to make different pistons for the EJ25 since it is bored out larger than the EJ22? IDK, just throwing something out there.

Regarding an STi block, that is actually a good idea. Only problem is the age-old question, how will my stock tranny (with an aftermarket clutch, maybe a lightened flywheel) hold up against the torque monster?

Regarding an EJ22T (IIRC it IS an EJ22K... I think), it does have experience in ultra-super-dooper boost levels over the STi block, but that is because not enough people have tested the EJ257's limits as they have the EJ22T (xphyr and his crazy 30+psi excursions on the street/track ). I think a EJ257 would be good enough for me ... hell, even an EJ20 would be. I just need to reduce the miles on my engine from... It just rolled passed 108,000 mi. today.

Take It Easy
-ben
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