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Old 03-26-2001, 12:26 AM   #1
RonOtter
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Post 2.5 Heads on a 2.2T block

I am currently rebuilding a 91' Legacy 2.2 turbo engine. I have read a lot on the possibility of placing 2.5 heads on the engine to increase flow (thanks to Cobb tuning for the great info). I am looking for opinions and perhaps more specifics on this subject. SOHC vs DOHC? What are the possible donor cars, any problems to watch out for, has anyone had direct experience, etc.

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Old 03-26-2001, 04:28 PM   #2
GTBGUY
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This can be done, but it'll be a wiring nightmare
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Old 03-26-2001, 09:42 PM   #3
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Wiring? I don't remember many wires going into the heads. Do you have to swap the intake manifold too? I could see where that could be a pain in the ...
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Old 03-26-2001, 09:45 PM   #4
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I ment "wiring" up everything (as in hoses etc..) Also, the ECU isn't used to the the different cam profile, so it could inject @ the wrong times...

Yes you'd need the intake manifold and heads from which ever EJ25 head you decide to use.
If you want to make a safe bet, I'd find the Phase 2 (SOHC) EJ25's heads, so at least it'll match up with your ECU (b/c you have a SOHC 2.2).
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Old 03-27-2001, 06:44 AM   #5
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I agree, there's no good reason to go DOHC.

The cam profiles might indeed screw up the timing of the injectors and spark. Maybe this is why most people doing this swap usually have a boatload of piggyback controllers or a whole new engine management system.

Then again, we could both be completely wrong.
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Old 03-27-2001, 09:13 AM   #6
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I can tell you from first hand experience that the DOHC heads and SOHC heads will fit and work... Only thing is that since the Engine is bigger (the orginal EJ25), it might have larger injectors etc... so there are many factors.

For simplicity sake, the easiest way to get more power is to extrude hone your intake manifold, heads and get a 3 angle valve job. Then get a electronic boost controller, larger downpipe, larger intercooler (if you don't have one), and a larger diameter cat-back
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Old 03-27-2001, 09:32 AM   #7
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Dale Teague is doing this in North Carolina Take a look: http://home.att.net/~teaguesauto/impreza.htm

He is a really cool guy and might give you tips and what to watch out for if you call.
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Old 03-27-2001, 02:05 PM   #8
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Dale is a cool guy and I have been having some correspondence with him on this subject. I am torn between the appeal of the new SOHC design and the hurdles presented by making the swap vs. the port and polish route. I suppose another thing to consider is how hard it would be to find someone who can port the heads correctly and the cost involved with that vs. the cost of the 2.5 heads/manifold and the troubles involved there. Has anyone tried this swap and have it running under their Legacy's hood?
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Old 03-27-2001, 02:18 PM   #9
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the only way to do this is if you get a dohc 2.5 car as the project that way you use the heads with the cam sensors and "wires" going to them with the 2.5 ecu and the 2.2t block thats the only way to do it where its not very difficult and expensive. also nobody knows yet if you can swap the cams sensors and such... the rule is all the blocks interchange but the rest gets scarry fast..
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Old 03-27-2001, 07:21 PM   #10
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Andre Vandenberg is running an EJ22 turbo block with the stock EJ25 DOHC heads in his 98 RS. I've driven it before, and it seems to run quite nicely.

I'm sure he'll have something to add to this conversation when he gets some time free.
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Old 03-28-2001, 09:26 AM   #11
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HOK has the SOHC EJ25 heads w/ the EJ22T block in his '99RS. So just to show it can be done both ways I personally prefer DOHC, and it's definately easier if you're starting w/ a DOHC car. Converting a SOHC to DOHC is a pain in the a$$, unless ofcourse it's a Honda
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Old 03-28-2001, 01:50 PM   #12
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Just ignore all those people who haven't done it. They just want to post as many times as possible. Putting the DOHC heads on will definitely work, but your compression ratio is going to drop to about 7.7:1. You also don't need any wiring bull***** if you're putting it back into the stock legacy trim. I suggest when you put the heads on (you'll also need sprockets, belts, tensioners, etc.) that you add an intercooler. That is the #1 upgrade for a legacy turbo.

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Old 03-28-2001, 05:32 PM   #13
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I have noticed that most of the replies are talking about swapping the 2.2 block into a car that is already set up to handle the 2.5 electronics/fuel system. This would seem to be a easier task as most of the 'wiring' happens at the top end. My main worry is fouling up my fuel injection, and getting the cam timing right.

I also find it interesting the seeming conflict on SOHC vs DOHC, from most of what I have read the SOHC head would be more compatible to my application (turbo).

I will be adding an intercooler soon after I get up and running, and I suspect that will be another interesting thread...
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Old 03-28-2001, 07:00 PM   #14
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SVX- how is it that you plan on using the sohc cam sensors for the dohc heads they won't be able to tell where the cam is. the two types of heads use different cam sensors... sorry just trying to get another post under my belt..
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Old 03-28-2001, 09:07 PM   #15
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I'm basically doing the same setup. Got the shortblock and am now just waiting to pick up the heads. Just want to know if you guys are planning on using the stock head bolts or are going aftermarket? ARP dosn't make them or studs for Subaru. I found a company in New Zealand that makes a stud kit for the 2.2 for $80 which isn't too bad. Also does anyone know any High pressure oil pumps that fit the 2.2 block? I know that the 2.5 is the same but I'm not sure if they flow the same. I talked to Adam Bloom but he wasn't too shure either....Gerry
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Old 03-28-2001, 09:37 PM   #16
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Now, now Bill and SVX!

You both have valid points. The question is will my 91' Legacy ECU work with the new heads? This is one of the reasons I am leaning to SOHC heads...

By the way, I always wondered what that monkey icon was

Gerry: I went ahead and have already bought stock head bolts, I think I paid more that $80 for them. I bought them when I thought I was just going to slap my original heads on. I will have to check and see if the length and torque ratings are the same for the 2.2 and 2.5 heads, if they are I would think that I could use my 2.2 bolts. I think that the 2.2 stock oil pump should be sufficient, I just bought a new one and from what I have heard it is rated to handle the heaver flow required by the turbo block. I think I will put a oil pressure gauge in as I could never figure out why I don't have one in the first place. (I hope I am not stepping on my helmet here, I have not been behind the wheel of this car in about 2 years, but I don't remember having a gauge!)

So are you dropping this engine into a Legacy?

[This message has been edited by RonOtter (edited March 28, 2001).]
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Old 03-28-2001, 10:13 PM   #17
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I'm new to Subaru's, but not to cars. I'm wondering about blocks and cranks. Are the EJ22 blocks and cranks stronger than the EJ25? Is that why people keep swapping it the smaller 2.2 litre engine? Also, is this 2.2 the same as the 2.2 in the earlier imprezas w/o the turbo? Is there a huge difference with any Subaru block except for size? I'm just confused, because they are all named EJxx.

Scottie
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Old 03-28-2001, 10:28 PM   #18
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Scottie:

The 2.2na and the 2.2t are different blocks. The turbo block is a closed deck block with a hardened crank, rods and better pistons. It is designed to handle the stresses of a turbo-charged fuel system. Check out
http://www.xmission.com/~dac/library/turbo_info.htm

for more info.
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Old 03-28-2001, 10:33 PM   #19
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Scottie:

the EJ22T bottem end from an 91 legacy is ...more reliable under turbo than a stock EJ25 bottem end because it was built for turbo charging.. (i wouldn't say more powerful)...

and NO all EJ22's are not the same the only EJ22 worth swapping into an newer impreza is one from an turbo 90-91(i think is the year..) legacy.. all the rest would be a waste...

and the block casting on the EJ22's is very different then that of an EJ25. or EJ20 depending on the year.. the decking is more solid on an old EJ22s..
if you get into JDM EJ20's there is a whole list of different changes made every year..

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Old 03-29-2001, 12:58 AM   #20
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ask ASR or B-SPEC they both have one
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Old 03-29-2001, 06:20 AM   #21
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The legacy turbo, all DOHC (incl WRX) and the model '99 SOHC heads have the same cam sensor. All use a cam sprocket with seven protrusions on it. Everything else bolts up. The 'CA' spec '99 SOHC and '00' and later SOHC heads use a 2 protrusion cam sprocket. So, you can bolt on the SOHC or DOHC heads easily. You just need to make sure your cam sprocket LH intake cam sprocket has the 1-2-1-3 protrusions.

svxtrem

The only real benefit of the DOHC heads over SOHC are that they are 'capable' of running higher RPMs. Valve sizes are the same. However, valves in either of these heads are 36/32mm- your legacy is only 31/28mm, so in either case, you will be seeing better flow- cams are also bigger.

[This message has been edited by svxtrem (edited March 29, 2001).]
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Old 03-29-2001, 09:28 AM   #22
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Thanks SVX, that is some good info. Do you know if any of those model engines had stock turbo chargers and if so, were there differences in the heads? I think only the 2.0l engines from overseas were turbo charged but I am not sure.

I know my stock EJ22T block has dished pistons that reduce the compression ratio, and my stock heads have modifications that differ from the 2.2NA heads to improve cooling and performance.
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Old 03-29-2001, 09:38 AM   #23
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If you're changing over to the EJ25 Phase 2 SOHC heads, you'll raise your compression from ~ 8.5:1 to ~ 9.2:1. You'll effectively have more low end Torque vs. using your old heads. Personally, for costs purposes, I'd go with extrude honing and head work... definately alot less effort, and definately no fit problems.
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Old 03-29-2001, 07:28 PM   #24
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Here we go again... DOHC vs SOHC any of you looked at the new WRX.... DOHC!! EVER seen a "high performance" factory race engine with a SOHC when a DOHC was available? Has the WRC car EVER run SOHC?
Granted, in our cars (NA) there is "little" difference between DOHC and SOHC BUT when the tuners start tuning the SOHC stays on the porch the DOHC boys are out there playing with the big boys... 'cept for Byron!! But he's a freak of nature, and I do think when we get enough beers in him he WILL admit that DOHC would gain him EVEN more HP.

I would try and run as many of the original sensors as you can. Makes for a much less stressful install and sort out.

I am running EJ22t short block, oil and waterpumps, with EVERYTHING else MY98 2.5 RS. So, yes in my case it was a MUCH cleaner and easier install THAT way. As far as turbo goes, I am using a Minnam Stage II kit. MOST people, unless I tell them, or they actually find the EJ22 on the block can never know that I did the swap.

Compression ratio.... I REALLY don't think it is down to 7.7 to 1 simply because:
1) The car detonates on pumpgas if I run more than 14 lbs of boost.
2) The compression is almost the same as what it was in the EJ25.
My guess would be more on the lines of 8 to 8.5 to 1

It is a good and cheap way to improve the RS, but the Legacy, I don't know. You may be opening an electrical can of worms if you don't use all the Legacy sensors, Then the Question also comes up.... How good are the Legacy ECU maps...?
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Old 03-29-2001, 08:39 PM   #25
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Andre Vandenberg - I beg to differ. IIRC, the Porsche 911 Turbo used to be SOHC H6, as well as the Ferrari Testarossa was a SOHC H12. Evening the Koeing Competition version w/ twin turbo and S/C was a SOHC H12.
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