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Old 11-04-2003, 05:58 PM   #1
4wheelflyer
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Default 2.5L DOHC heads on EJ22T block

I was told they would bolt up no prob, but I would like to hear from any one who HAS this set up. is there any problems ? do they fit well ?is there any blockage of coolent between the open deck heads and the closed deck block? any blown head gaskets ?
sorry for all the questions but I would like to hear from some one who has done this, could save me alot of trouble in the future

many thanks ....4WF
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Old 11-04-2003, 07:48 PM   #2
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try a search for Xepher... he has the dohc heads on an ej22t. He actually builds them (and has gone through several) and puts around 450bhp out with the setup (at like 23psi). I talked with him briefly once, he said the dohc flows the best for stock (the ej22t heads are crap when uping hp levels)

anyhow, look for that dood - he has mucho knowledge

-Chad
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Old 11-05-2003, 04:54 PM   #3
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thanks Chad, this seems to be the way to go for a bomb proof motor, Ill do a search and see what I can find
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Old 11-08-2003, 08:16 PM   #4
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Make certain that you at least port the heads. I don't remember who posted it, but a few years ago someone posted flow charts taken of the 2.2T heads, the DOHC 2.5 heads, and the SOHC 2.5 heads. The SOHC heads outflowed the others. If I remember correctly the 2.2T heads were second.

We have a turbo legacy with a multi angle valve job and full porting on the heads and it is excellent as is. The car has a TDO4 and a stock WRX uppipe, scoobysport downpipe, and a custom rear exhaust. At only 12 psi it will outrun a stock WRX handily.

The point I am trying to make, is to make certain you are doing the right thing by swapping heads, when you may actually be hurting yourself.
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Old 11-08-2003, 11:20 PM   #5
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Quote:
Originally posted by Templar
Make certain that you at least port the heads. I don't remember who posted it, but a few years ago someone posted flow charts taken of the 2.2T heads, the DOHC 2.5 heads, and the SOHC 2.5 heads. The SOHC heads outflowed the others. If I remember correctly the 2.2T heads were second.

The point I am trying to make, is to make certain you are doing the right thing by swapping heads, when you may actually be hurting yourself.

Ya... I would just get a set of RS SOHC heads, rather then port the 2.2 heads or 98 DOHC heads. A good port job is going to cost 2kish. There was a good thread a while back in aftermarket FI on porting and its pros and cons.
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Old 11-09-2003, 06:04 PM   #6
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hmmm well looks like I have to do more research, I thought the DOHC flowed the best ,well I wonder how much difference there is anyways , so the 2.2L T heads came in second for flow ,maybe I will just get those worked on since they will come with the motor any way. Im not trying to build a 500+ hp beast, Im thinking more like 300 BHP ,Im sure the 2.2T heads will be fine for that

and I searched for Xepher ,did not find anything but sent him a PM no word back yet
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Old 11-09-2003, 08:13 PM   #7
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Old 11-10-2003, 06:40 PM   #8
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cool thanks totoherbs ill check them out ,so I heard back from Xepher and got some really good info from him
now I have to figure out the whole ECU thing....

thanks....4WF
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Old 11-11-2003, 06:42 PM   #9
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good links ,its good to know about different valves, springs and cams and how worth while the can be
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Old 11-12-2003, 11:56 AM   #10
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Old 11-12-2003, 03:03 PM   #11
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nice charts Jon....any of the older EJ20 heads?

I have EJ20G DOHC heads on the way back to me right now with lots of titanium bits inside
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Old 11-12-2003, 03:18 PM   #12
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...and here is the writeup on the pics that Stimpy posted. http://www.cobbtuning.com/tech/sohc/index.html
Very nice article.

Alan - We got Omar's car running OK with the LINK! I'm still learning everyday on how to work with it, currently it's running pigrich! (Now I know what headaches I'm gonna have once mine is back together!)
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Old 11-12-2003, 03:26 PM   #13
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thanks Vic....too bad there is no info on the flow DOHC heads yet
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Old 11-12-2003, 05:52 PM   #14
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The main benefit of the DOHC 2.5 heads is that the cams have more duration so they provide better top end than the SOHC heads do.
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Old 11-12-2003, 06:39 PM   #15
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ya it would of been cool to see the DOHC 2.5 bench flowed too
but the 2.5 SOHC flow really well better than the LS1
to bad the 2.5 DOHC heads dont have roller rockers too
I will see if I can find a flow chart for DOHC's
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Old 11-13-2003, 06:58 PM   #16
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no luck yet ,any one have any flow info on the 2.5 DOHC heads?
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Old 11-14-2003, 06:44 PM   #17
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I am possitive I saw the flow tests for the DOHC and SOHC on Cobbs site a while ago... and the DOHC edged out the SOHC, not by much but they did.

and yea, the DOHC has a better Top end (5500rpm plus) and revs to 6450 (a whopping 200rpm more than the SOHC ) but the DOHC has about 10-15ftlbs less torque from idle - 4500rpm.

I'm going to check the Cobb site again

-Chad
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Old 11-14-2003, 07:01 PM   #18
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Quote:
Originally posted by Farfrumwork
I am possitive I saw the flow tests for the DOHC and SOHC on Cobbs site a while ago... and the DOHC edged out the SOHC, not by much but they did.

and yea, the DOHC has a better Top end (5500rpm plus) and revs to 6450 (a whopping 200rpm more than the SOHC ) but the DOHC has about 10-15ftlbs less torque from idle - 4500rpm.

I'm going to check the Cobb site again

-Chad
I remember reading something like that.... Im not sure if it was cobbs site or not....
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Old 11-18-2003, 02:00 AM   #19
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I'm looking into this swap too. 4wheelfyyer have you found anymore info about the mating of rs dohc blocks. I have a 98 and want to do this. I have a chance to get a complete 92 ej22t with 70k on it for $800 and a brand new WRX topmount with piping.
This woudl satify me for a bit as I would be buying a link ecu I think and maybe a vf22 or even just a stock wrx td04. Let me know what plans you have so maybe we can share info and help each other out. Thanks
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Old 11-19-2003, 06:51 PM   #20
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sime, sorry for not gettin back to ya sooner, I think I will go with the DOHC 2.5L RS heads, so far I think they are the best for higher HP levels, but that is a good deal for that motor and I would go for it if every thing was working well
feel free to PM me if you want......4WF
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Old 11-22-2003, 06:28 PM   #21
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my next question, if I have a (01 TS with MAP) EJ22 NA car and put a EJ22T motor with DOHC 2.5L heads in it, will I be able to keep my stock wiring harness and add piggy backs to cantrole fuel, boost, timing ect... or use a standalone? is this possible?
Id rather not have to pull the stock wiring harness out and swap it
so what do you think?
many thanks .......4WF
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Old 11-22-2003, 06:46 PM   #22
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4wheelflyer,
From a management standpoint you can run this like any of the piggy backed RS-T's out there. Personally, I would seriously consider running stand alone on that set up. It will be way more stable and controllable.

Also, I imagine that Marc told you that your CR will be in the mid to low 7's and that you will need to run a ton of boost and your bottom end will still suffer? I am looking at building my Legacy Turbo next summer some time. Initially I was thinking DOHC heads but now am looking at the SOHC EJ25 heads. Not only do they flow better, but there is a little less volume under the heads which will aid with the CR. It's something to think about.

It also depends on what pistons I decide to use. changing the pistons can solve the CR issues, but then you need to deal with working on the bottom end. Keep posting as your project progresses. There are a number of us doing these kinds of builds and information is going to become more available over time.

http://bbs.legacycentral.org/viewtopic.php?t=14314
And there's a little detail about Ciper's build...
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Old 11-23-2003, 02:02 PM   #23
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I recently bought a car that has a motor from marc ramirez. While I am new to the subaru tuning world, I am a huge forced induction geek. You will absolutely want to use the DOHC heads even if the SOHC heads flow slightly better. The reason for this is because the 2.5 motors have cams that are designed to run naturally aspirated. On a naturally aspirated motor you want a big cam overlap... however with forced induction you want just the opposite, a big cam overlap will result in you blowing alot of your intake charge right out the exhaust port as soon as there is positive pressure in the manifold....
With a DOHC valvetrain you can very easily play with different exhaust/intake cam advances to get rid of this overlap. Personally I have seen power gains of close to 5% completely across the board, and dramatic increases in fuel economy and much less backfiring coming off the throttle. And if you are running a cat.... it will last much much longer when it's not getting saturated by un-burnt fuel. with the SOHC heads, the only way to control overlap is have an entirely new cam ground every time you want to move the cam timing around because the intake/exhaust are locked into one another. So yeah.... an SOHC head might flow slightly better.... but it's all wasted if you can't take advantage of it.

4wheelflyer as for your question about engine management, don't even think about using an EJ22 NA ECU on EJ25 heads, unless you did a complete ECU re-flash there is no way the thing would ever run right. if you could dig up an EJ25 ECU there are a few tricks you can do to make it run quite well (previous owner of my vehicle did this, and I'm still running it until I can get the money together for a standalone setup)
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Old 11-23-2003, 06:25 PM   #24
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hey thanks for the info guys
Im thinkin a standalone would be the best for what I want , there is going to be a lot of things I will have to get tuned right and sounds like I need the tunability of a standalone. Im still going to use the DOHC heads for the better top end ,but Im not sure what head gasket to use ,I think the EJ22T gasket because I would like to keep the CR in the 7's so I can run some meca boost, but Im going to try to build somthing that will spool up really fast so I dont have to worry about the loss of low end torque.
back to the electronics ,so if I get a standalone I will just have to swap out the stock ecu for the SA and run some wiring for the turbo's ect...I know this should be in the tuning section but this is part of the conversion and the faq's are kinda vauge in that forum
NCP so you have one of marks motors, niccccce ,so how do you like it? does it have DOHC heads on it too? how is it treating you, reliable, good HP ect... let me know what you think

thanks.....4WF
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Old 11-23-2003, 07:37 PM   #25
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I wish I could tell you how the motor was treating me 4wf, but the car is sitting in my garage awaiting plates

I've gotten the chance to sneak it out a few times around my house and I must say that power is well.... scary. As for reliability, the previous owner ran the thing for ~30,000 miles until it came into my hands... and the car is running some badly hacked together engine management, but it still runs flawlessly, not even any of the famous subaru ticking.

*insert geeky ramblings*
As for head gaskets.... your compression doesn't really effect your spool up times at all, because there is a nearly identical gas volume leaving the cylinders to spool the turbo regardless of compression. Believe it or not.... torque is almost totally un-affected by compression, and horsepower is effected by compression less than you would think. I got my start with silly powerful motors in the honda world, and you can raise the static compression of a B18C1 (integra GSR) motor from 10:1 out of the box to 11:1 all the way up to 11.5:1, and still only see single digit horsepower gains. but with the increased compression you now have to worry about the evils of detonation all that much more.... it's not all bad though. Raising your compression will make a motor much more responsive (so you might want to sacrifice a few pounds of boost if you are going to need a super responsive autocross motor). And fuel mileage will get a big bonus (this is why auto manufacturers are always bumping compression, because a compression increase allows them to make more efficient, cleaner burning motors) But as for your "low end", the 7.5:1 motor is just as easy to drive around town as any other impreza I've driven (I was in the market for 6 month and drove every one I could get my hands on until the perfect one dropped in my lap) and it's also got a 3" exhaust. Turbo lag on the setup is almost non-existant with a VF22 turbo. Any turbo subaru is going to be much less laggy than an equivalent setup on any other type of motor because of the huge oversquare we are running (short stroke with a really wide bore, that huge oversquare is what made me ditch the honda world) because turbos like to spool with very short hard exhaust pulses rather than long drawn out pulses. I'm at full boost (22lbs) by 3500 RPM's, and the VF22 isn't a very light compressor wheel, so it really likes to stay spooled once it's spun up.

Yeah I know I'm kinda generalizing here.... but unless you are really concerned with some of the tiny nitpicky stuff that would come with building a full blown race motor.... the generalizations will work.
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