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Old 05-14-2003, 08:46 PM   #1
NewbyScooby
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Question Can I put a 2.0 head on a 1.8 block?

Hi,



I wanted to put a twin cam turbo ej20 head on my 1.8 liter. I am in the process of turbo charging it and I figured that I would get better gains if I put on a much better flowing head. Will the head cylinders line up, will the timing belt fit all my preexisting accessories? What manifolds will fit. When I swap can I temporarily use my 1.8 manifolds until I get some wrx exhaust and intake manifolds or will I have to put the new ones on with the new head?


Any info would help.

Thanks

Tom
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Old 05-15-2003, 02:05 AM   #2
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I have no idea if the EJ18 intake manifold will work with the EJ20 heads... They might bolt on, but the EJ18 heads are in two pieces and have alot of plumbing attached to them that might need changing.
The exhaust ports are in the same spot with the same bolt pattern, im pretty sure on that one, so you can just bolt up whatever you need along those lines, which would probably end up more like RS-T exhaust work using one of those custom uppipes to the turbo.
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Old 05-15-2003, 10:00 AM   #3
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In a word, NO. They will not fit, I tried already to bolt the WRX DOHC heads to every block Subaru has made for NADM.
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Old 05-16-2003, 01:45 AM   #4
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Quote:
Originally posted by damianq
In a word, NO. They will not fit, I tried already to bolt the WRX DOHC heads to every block Subaru has made for NADM.
Any details on this? Like maybe some pictures or an explaination?
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Old 05-16-2003, 09:05 AM   #5
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Sorry, no pics. The heads DO physically fit on top of the block. But the fluid passages do not line up correctly, making head gasket selection extremely difficult. While you might get "some" fluid (oil & coolant) flow, it will be very restricted. The older 1.8 blocks had relatively small/restrictive passages fluid anyways. The best match I have found so far is the Legacy Turbo block (EJ22T) w. the WRX heads using a V3 or V4 STi head gasket. Almost no port matching is needed. Contrary to pop. belief the early 90's EJ22T was NOT just a bored out 1.8L block. It is a completely different motor. Hope that helps.

FWIW, the best flowing heads are the phaseI EJ25 DOHC heads if you're talking pure volume. Of course, genuine EJ20 STi heads flow much better/faster but do not carry the volumetric efficiency of the EJ25.

Last edited by damianq; 05-16-2003 at 09:11 AM.
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Old 05-17-2003, 02:44 AM   #6
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Ah, ok, that makes sense. So some work would be required to match up the channels for say an EJ20 gasket to work along with the EJ18 block, but the bolt locations are identcle... I would think that the larger EJ25 heads would have trouble bolting up with smaller blocks though, as the pistons are much smaller than the ports, but I dont know that much about the specifics and thats why I'm asking for details so I can learn more

But would you think it would be possible to modify either the EJ18 block or EJ20 heads to fit better with either an EJ18 gasket or EJ20 gasket (depending on which one has better flow)?

And ya, the EJ22's are different motors, but I havent seen anything to show that an EJ20 isnt a bored out EJ18 yet
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Old 05-17-2003, 02:04 PM   #7
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I should clarify something here. It's not that one head gasket or the other won't match up. It's that the passages on the block are physically offset from those on the head. No matter what head gasket you might use the passages still won't match up. Subaru uses the same head bolt spacing on pretty much all the blocks and heads. This just make manufacture tooling much easier, not to mention head design modifications for the future. It is much easier to improve upon something when certain variables are fixed & you know what you have to work with.

You could NOT use EJ25 heads on a EJ18 block. The valves would hit the block deck when they open. You would have to bore the EJ18 to, at least, 94mm, in which case you now have an EJ22 block. As for putting WRX heads on an EJ18. Yes it will fit. NO, it will not work. That is unless you think coolant and oil flow are not neccessary.

Another thing is that both the DOHC and SOHC EJ25 heads are physically shorter than the WRX heads. This is in reference to stack height. The WRX heads flow much "faster" by having straighter intake/exhaust ports to/from the combustion chamber. Conversely, all other N/A heads in the N. American market are considerably shorter. Both EJ25 heads flow more "volume" than the WRX heads b/c the inlet and outlet ports are much larger but they are shorter & curved. This curvature reduces the air velocity thereby reducing the flow numbers but the ports are still very large making up for lesser velocity.

That being said the DOHC EJ25 heads in particular flow more overall volume than the WRX heads at the same pressure. Now remember that the WRX heads are designed for pressurized air. For efficiency/reliability sake, it makes sense that you would want to get pressuresized air in and out of the combustion camber ASAP. For a turbo, the rising, accerative rate of combustion is greater served by high speed rather than volumetric efficiency. For N/A combustion is better served by volume rather than velocity. Sucking vs. forced induction.

BTW, the block Subaru uses for N/A is completely different in design and many characteristics than the 1994cc turbo block, which is different. The difference is obvious when you look at them side by side.

The EJ18 is one block. The EJ22T is another completely different to anything else, although some might arugue it's closer to the EJ18 than the newer EJ22. I belive it was a test bed for new design features to arrive later on the N/A EJ22. The EJ22 is the completely re-engineerd version of the N/A EJ18 block but different in many vital ways & remained unchanged until 2000 when they dropped production of it in favour of the PhaseII EJ25. The PhaseI EJ25 is a bored and stroked version of the EJ22. The PhaseII EJ25 has some minor tweaks in the name of efficiency & strength & is still currently used for N/A applications. The EJ20 turbo block has remained largely unchanged since 1993. Remember, we're talking just blocks here.
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Old 05-17-2003, 10:54 PM   #8
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Two more questions:
1. As you state that the coolant channels are completely different, then that means that there isnt a way to modify either the block or the heads to match up the channels of the other part of the engine? IE modify the channels on an EJ18 block to match the EJ20 head, or modify the EJ20 head channels to matt up with the EJ18 block? Or is it that they are in such completely different locations that it would be impossible to do?

2. You stated that the WRX EJ20 heads are designed specifically for turbo aplications, so even a WRX EJ20 without the turbo (kept in N/A form) would not work well as an N/A motor even with cam, valve, piston, crank, etc. modified parts because of the fundamental design of the WRX heads to flow best with turbo use?

Bonus question: I was talking about this subject today, and wiring harness issues were brought up. If an older block designed for OBD-I wiring was matted to a newer heads that were designed for a newer OBD-II car, would there be impossible issues with the wiring or would it be overcomable?
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Old 05-19-2003, 01:16 PM   #9
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what about putting the EJ25 DOHC phase1 heads on the SOHC phaseII block?
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Old 05-19-2003, 08:25 PM   #10
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Quote:
Originally posted by Kostamojen
Two more questions:
1. Or is it that they are in such completely different locations that it would be impossible to do?
Different enough that it is not worth the time, effort or money.
Quote:
2. ... as an N/A motor ... the fundamental design of the WRX heads to flow best with turbo use?
Correct.
Quote:
Bonus question: wiring harness issues ... would it be overcomable?
With a proper wiring diagram, it's only requires diligence... just like a Silvia swap.
Quote:
Originally posted by trojan9x
what about putting the EJ25 DOHC phase1 heads on the SOHC phaseII block?
Same block, only minor efficiency mods made. No problem.
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Old 05-19-2003, 10:45 PM   #11
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Ok, good stuff... Thanks for answering my q's

I think ill just shoot for a cheap EJ22 and see if I cant try out that MY96 rocker arm swap...
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Old 11-18-2003, 07:10 AM   #12
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So ya, I havent found anything to back up your statements damian... And as far as I can tell, the coolant channels are identicle on the EJ18 and EJ20. I need more info or your theories are going out the window.
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