2.2 Heads on a EJ25 More info please.

[RNandKT]

Hey guys I'd like to get some more info from you hybrid guru's. I am in the process of doing the head gaskets on another 97 LGT, and I am thinking of pushing things a bit this time. I wanted to have the cams done and shave the heads a bit to puch the compresion ratio, but I keep finding threads of swapping on 2.2 SOHC heads instead. I understand this pushes the compression ratio a little but have a few questions.

First what is the stock compression ratio and what does it push it too?

Second are there any downsides to switching to the SOHC?
(note - I know that it's best to get pre 97 non turbo heads to retain the dual port, and also having cams weld-on/reground is cheaper cause two less cams, but any other advantages/disadvantages of these heads?)

Lastly has onyone actually done this that has some tips to pass along?

I have no intentions of ever going turbo as it's just not worth the headache (I'll just buy a wrx if I go that route.) but I though since I'm there a couple of extra stuff like bumping the compression porting the intake and exh ports and hotter cams might be well worth the extra couple hundred bucks. Then I could always add a header and CAI and cat back exh and etc etc later.

[Sarra]

Your compression ratio should be 9.7:1, though there was some variation.

SOHC vs DOHC... Well, it depends on the heads. They both flow "well", though the SOHC 2.2 liter heads don't flow as well the 2.5's heads.

SOHC has 2 cams, as opposed to 4 cams in DOHC, so you have less rotational mass and fewer moving parts with S, but D has, from what I remember reading, a better top end than S.

If it were I doing this, I'd grab a set of cometic headgaskets, and ask them to give you as thin of a gasket as they possibly can.

I don't remember how high of a CR the 2.2 heads on a 2.5 block will get you, but it's above 11:1 and below 14:1, but my memory isn't singling out a specific number between them. =\

[AJM]

Between 11-13, I think it's 12 ,but i'm not 100% on that.

Ej22 heads don't flow as well, esp. dual port ej22 heads. If you were to do this hybrid, you might wnat to consider a good port and polish for the ej22 heads.

Unless it was MLS, I woulnd't go with extra thin head gaskets on an ej25 espailly if you drive agressively. Lets review here, the ej25 has a bad block design period. This is fact. This block was made to blow head gaskets.

[Sarra]

The EJ25D, or all NA EJ25's, or all EJ25x engines?

[RNandKT]

12 to 1 is still probably acceptable to run premium right? Also which SOHC heads are better the single port or dual port.

Any chance anyone knows how much can be taken off the DOHC heads to increase the compression ration up around 11 to 1?

Thanks for your help

[AJM]

12 to 1 is still probably acceptable to run premium right? Also which SOHC heads are better the single port or dual port.

Any chance anyone knows how much can be taken off the DOHC heads to increase the compression ration up around 11 to 1?

Thanks for your help

I don't know how much can be shaved the dohc heads.


This will be much debated, but I belive the single port has bigger valves, however, aftermarket suppoert is better for dual port.

[AJM]

The EJ25D, or all NA EJ25's, or all EJ25x engines?


I haven't taken apart any of the newest ej25's, but any of the 1995-1998's....it's the way the deck is made. Too much pressure builds behind head and...pop goes the head gasket.

I have one source that says subaru never fixed the block itself, but instead switched to mls gaskets and increased tourque ont he head bolts to make sure it doesn't happen on anything above 1998ish.


If anyone wnats a visual source...I can present one.

[Svenerachi]

the best advice i was given on here when i was talking about doing a frankenstein build came from Scott Siegel (helping to tune my car)

he said just start saving for an engine swap, because thats what you're lookin at eventually. if you start mashing the bits together you're going to be spending more money on tune supporting mods and dyno/tune time than you're saving. for example, to run the 2.5 motor and 2.2 heads he was saying i would need stand-alone EM, a custom tune, custom blah blah blah and a shit load of other small things in order to get it to run reliably.

if you're just wanting to make it go fast for one or two runs down the track, by all means, but i wouldn't(and neither did Scott Siegel) suggest doing this to your DD

[Plays_with_Toys]

^^^ Not true. A friend is running his 94 2.2 heads on a 2.5. He's about as junkyard dog as they come. 20,000 miles later and it is still running like a champ. This is with no supporting mods except exhaust. He runs premium fuel though, and we are altitude which helps.

[StatGSR]

im planning on doing this in the fall. 98 2.5 block, my single port heads. but if you have a 2.5 block and heads, there is really no benifit to swaping to 2.2 heads, the 2.5 heads flow better. and you will have to run premo with the hybrid. also iirc the CR is around 11.5:1 with the hybrid.

as for debate between the 2.2 heads the single ports have larger valves than the duals and flow a little better. also the singles have solid valve lash adjusters vs the hydrolic valve lash adjusters of the older dual ports.

[Svenerachi]

why was ^ statgsr banned? or is that just his unique status thing?

[RNandKT]

All good info, on one hand I like the bonuses of the CR or the hybrid, but as pointed out it would be nice to stick with the DOHC heads since they flow better and there is more support for cams and headers etc. I just wish someone knew how much can be shaved off them to get somewhere between 10.5 - 11.0 to 1 CR

Well thanks for all the info.

[tekkitan]

why was ^ statgsr banned? or is that just his unique status thing?

he was a naughty monkey :lol:

[StatGSR]

^what he said... :grin:

[Reason]

naughty monkeys are not tolerated here :lol:

[Plays_with_Toys]

i
as for debate between the 2.2 heads the single ports have larger valves than the duals and flow a little better. also the singles have solid valve lash adjusters vs the hydrolic valve lash adjusters of the older dual ports.


where have you heard this? The valves are larger, but from what I read the flow rates were about the same. There was a thread talking about how to enlarge the exhaust port to get even more flow, however, you'd need a custom gasket made to accomodate the larger hole. Oh and my single port heads have hydraulic lash adjusters ;)

[bakergtt]

Also your intake manifold for your 25 wont bolt up to 22 heads. Know from experance right now as my engine is being rebuilt.
Also I think you would have to look at getting a different exhaust header as I believe the 22 and 25 are different (not sure though)

I have been told by a couple of guys that have done hybrid engine turbo build ups (300whp+) that the SOHC flow better then the DOHC (dont know why) and thats why I tried to go with them but i would have to change alot more then just the intake manifold (fuel rails, injectors, etc)

I suggest sticking to your stock heads and if you want more power get some aftermarket parts for your heads (cams, springs, etc.)

[StatGSR]

where have you heard this? The valves are larger, but from what I read the flow rates were about the same. There was a thread talking about how to enlarge the exhaust port to get even more flow, however, you'd need a custom gasket made to accomodate the larger hole. Oh and my single port heads have hydraulic lash adjusters ;)

i heard from the interwebs.... so it must be true? also the gasket bore is a fair amount larger than the single port bore iirc.

as for the single ports with HVLAs, thats news to me... i thought that was part of the "change".

[Plays_with_Toys]

My car is a bastard child. I'm still waiting to open up the center console and see what type of shifter I have...

[Jedi Taxi]

well, you can still use pump gas all the way up to 12.5:1 CR

I suppose the way you could do this is by shaving the heads a bit and throwing on a 2.5L MLS head gasket that is at the stock thickness.
However, that would only get ya a 11:1 CR and still would mabye get ya another 40hp. That would get to around the area of 200hp, mabye more. But still, this is an interferance engine we're talking about here, when building it back up, you better be damn sure your timing is right.

[theboyo19]

im also interested in doing this
i have a 25 dohc out of a 99 sus that has blown headgaskets and my 95 lsi has a 22 sohc thats dying and needed a rebuild .
would it be worth it to put the heads on .. im assuming its a bit harder than just switching heads

[StatGSR]

^ not really, everything i have read says, put 2.2 heads on 2.5 block, use stock 2.2 ecu and run premo. only thing i still need to learn for sure is which head gasket to use, i think im suppose to use the newer thinker 2.5 but i still need to ask about that.

[subienubie]

What if you used the 2.2 turbo heads and and turbo with a thicker head gasket and ran low boost would this work well???

[StatGSR]

What if you used the 2.2 turbo heads and and turbo with a thicker head gasket and ran low boost would this work well???

high compression and boost gets tricky, would definatly require engine managment and a good tune and would still be hard to pull off on pump gas. it would probably end in poping the motor if you didnt add some strength to the bottom end.

[subienubie]

well i was talking more along the line of dropping the compression to a safe lvl with a thicker head gasket and trying to run the 2.2t ecu??? would it be worth the extra trouble and would i see much hp gain???

[Sarra]

well i was talking more along the line of dropping the compression to a safe lvl with a thicker head gasket and trying to run the 2.2t ecu??? would it be worth the extra trouble and would i see much hp gain???

You would have the thickest headgasket ever.

You could do pistons, though, I'm not sure that would work well either. You'd probably have to do crank, rods, pistons, and headgaskets for an EJ22T head on a 2.5 liter block.

[Jedi Taxi]

Pistons would be a must.

Most of the time, high compression + boost = bad detonation. lets say you built up a 11:1 ratio franken motor. then you slapped on a T25. basically, just to keep it from detonating so bad, i would say you would need a AWIC, great engint managment, and alot of fuel (huge injectors).