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Old 09-17-2007, 12:45 AM   #1
morrocco88
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Default STI Block EJ20G heads?

I know this had been answered before, but I searched for many hours and got nothing good.

Would it be a good idea to use 20G heads with the hydraulic lash adjustment on an STI shortblock, and what head gaskets would I use, and what would the approximate CR be?

I've also thought about using the Phase 1 EJ25 heads off a 97 LGT, but I just don't know which would be better for bottom end performance and reliability. This will be a street car focusing on torque, and not concerned about top end HP. I also have an extra set of low mileage 20G heads right now, so I was leaning toward them.

The other thing is that the Ej25 NA heads seem to be a little noisey. I have changed all the shims on the buckets on my wifes 97 OB to get all the valve lash adjusted to spec, and it had little effect on quieting things down. Cold start up is still pretty noisey. It used to worry me but have since come to the conclusion that this is just the way they are. The 20G heads are a lot more quiet and makes the motor sound a lot more healthy overall.

So any suggestions or input would be appreciated. Help me build my long block!
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Old 09-17-2007, 01:09 AM   #2
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It works out pritty well.

Use EJ20G head gaskets, and it will all work perfectly. CR if I remember correctly is 9.1:1

It works AWSOME!
My friend with that settup made 50WHP more at 3200RPM with identical settups and on the same dyno the same day. Vs. my standard EJ20G.
By redline the HP numbers where almost identical, but the TQ out of the EJ25 is out of control!
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Old 09-17-2007, 03:10 AM   #3
morrocco88
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Thanks - That sounds really good! Torque is what I'm after. How long has your friend been running this setup? Any drawbacks to using the 20G heads? What was his setup like and total torque number? Thanks!
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Old 09-17-2007, 03:26 AM   #4
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Quote:
Originally Posted by snowman4us View Post
It works out pritty well.

Use EJ20G head gaskets, and it will all work perfectly. CR if I remember correctly is 9.1:1

It works AWSOME!
My friend with that settup made 50WHP more at 3200RPM with identical settups and on the same dyno the same day. Vs. my standard EJ20G.
By redline the HP numbers where almost identical, but the TQ out of the EJ25 is out of control!
ej20g heads on a 2.5 sti block...mmmmm,interesting. Do you have a dyno chart comparing these two?
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Old 09-17-2007, 05:58 AM   #5
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Quote:
Originally Posted by snowman4us View Post
It works out pritty well.

Use EJ20G head gaskets, and it will all work perfectly. CR if I remember correctly is 9.1:1

It works AWSOME!
My friend with that settup made 50WHP more at 3200RPM with identical settups and on the same dyno the same day. Vs. my standard EJ20G.
By redline the HP numbers where almost identical, but the TQ out of the EJ25 is out of control!
If you use ej20g head gaskets you will have an overlap into the cylinder of the ej257. I would assume this would lead to pre-mature failure. But other then that it will should make good power. Just use the thick ej25 gaskets as the ej257 gaskets are half the thickness of the ej25 NA gaskets. The head CC of the ej20g is alot less then the ej257 so you will get a raise in compression no matter what but the thick gaskets will be a good choice.
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Old 09-17-2007, 10:00 AM   #6
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Quote:
Originally Posted by Brydon View Post
If you use ej20g head gaskets you will have an overlap into the cylinder of the ej257. I would assume this would lead to pre-mature failure. But other then that it will should make good power. Just use the thick ej25 gaskets as the ej257 gaskets are half the thickness of the ej25 NA gaskets. The head CC of the ej20g is alot less then the ej257 so you will get a raise in compression no matter what but the thick gaskets will be a good choice.
Is that your setup?
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Old 09-17-2007, 11:35 AM   #7
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In all my searching, it seems as if people say to use the stock STI head gaskets when using the Phase 1 2.5 NA heads, so it would be nice if someone could chime in with some hard facts of what gasket to use. And maybe someone out there is running this setup? What are you using and how long?
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Old 09-17-2007, 04:12 PM   #8
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paging suberboy...

noah you out there?

which gaskets did you use
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Old 09-17-2007, 07:37 PM   #9
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well im building a ej257 bottom end with ej20h heads(same as ej20g). With a stock sti headgasket your looking at about a cp of 9.7:1. FYI-the cc of a ej20g head is about 7cc less than usdm WRX.As someones else stated using a ej20g head gasket, you would have overlap. My advice is to either buy a cometic sti gasket that is 1.3mm or 1.5mm.
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Old 09-17-2007, 09:04 PM   #10
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Quote:
Originally Posted by 99WRXEJ20 View Post
well im building a ej257 bottom end with ej20h heads(same as ej20g). With a stock sti headgasket your looking at about a cp of 9.7:1. FYI-the cc of a ej20g head is about 7cc less than usdm WRX.As someones else stated using a ej20g head gasket, you would have overlap. My advice is to either buy a cometic sti gasket that is 1.3mm or 1.5mm.
Exactly correct. That is why I went to USDM WRX heads on both my car and my Buddys Legacy turbo. It keeps the compression up but not through the roof. Although on my track car I run 9.2:1 compression but that's a little high for most.
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Old 09-17-2007, 09:23 PM   #11
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Quote:
Originally Posted by Brydon View Post
Exactly correct. That is why I went to USDM WRX heads on both my car and my Buddys Legacy turbo. It keeps the compression up but not through the roof. Although on my track car I run 9.2:1 compression but that's a little high for most.
exactly why I am saving up to switch heads/wiring and such. Old school JDM heads are a PITA to deal with.
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Old 09-17-2007, 10:45 PM   #12
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Well I'm sticking with the 2.5 na heads, or the 20G heads, so I can continue to use my Intake manifold and sensors. I don't want to have to swap the wiring and start over again I'm basically looking for more displacement to get the torque. I just want to drop in a new long block and get it re-tuned with the same setup I have now.

So what I'm getting here is one guy says use EJ20G gaskets, and two other say it will cause an overlap into the combustion chamber. And someone else says to use Cometic STI gaskets that are either 1.3 or 1.5 mm thick, and the stock sti gasket will give me about a 9.7:1 CR. So is the cometic 1.3 or 1.5 thicker than stock, to lower the CR back down a little? So I wonder what that would bring the CR to?

How about pros and cons to 20G heads vs phase 1 2.5 na heads, as far as lifter design and noise. I saw the Subie Sport project 1996 LGT is using the stock heads mated to a sti short block using the stock sti gasket, but custom pistons were used to get the CR where they wanted it.
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Old 09-18-2007, 02:17 AM   #13
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Gasket thicknesses are as follows. STI = .50, All other are 1.37, Cometic makes gaskets in a variety of flavors. the 1.3 or 1.5 would both work well and keep the compression just under 9.0:1.

And always use a gasket that is sized for the shortblock not the heads. IE 2litre gaskets hang into cylinder walls. But this is easy to tell. Just put the gasket on the block and run your finger up the cylinder wall. There will be a lip.
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Old 09-18-2007, 12:28 PM   #14
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Thanks Brydon - That sounds good. So just get the cometic gaskets in either a 1.3 or 1.5 mm thickness, and I will be just under 9.0:1 huh? I think that is a good CR to be at. I'm not looking to run crazy amounts of boost so it shouldn't be a problem. I'm going to be running a small turbo too, the VF28. If I could get around 300 foot lbs of torque at the wheels, I would be a happy man. And to get that torque the sooner the better. This car never revs past 6k anyways, so just street friendly down low goodness is all I'm after.

What about the pros and cons with the 20G heads vs the 2.5 NA heads? Anybody have a preference and why?
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Old 09-18-2007, 12:45 PM   #15
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which 2.5 na heads
there are a few flavors of phase 1
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Old 09-18-2007, 05:02 PM   #16
morrocco88
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2.5 na heads off like a 97 Legacy, or 2.5 rs of the same year. The ones with the shim on bucket lash adjustment.
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Old 09-19-2007, 11:34 PM   #17
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The overlap is a few mm all the way around the edge of the piston that has a flat spot on the head. The thicker HG just moves the flat spot that thickness away from the piston. With the thicker HG you can cool that area down, but still run the risk of hot spots. Hot spots can cause per ign. and kill pistons. Even with your overall CR being 9ish, the outter edge of the piston has a very high CR. I have seen it kill a few pistons, mainly taking out the ring land area of the pistons. I would say you are going to be "safer" using a 2.5 head, but there are many cars that run a 2.5block/2.0heads and make fairly nice power. A buddy of mine, has worked for/with ESX and many other subaru shops, has a 16-17psi rule. He has seen many many 2.5/2.0 go after they push that psi limit. I didn't believe him and ran 18 psi (to get a 400awhp pull) and I killed the engine. I now run a full STi longblock swap, with the AVCS.
MCL

Last edited by WickedRydaX; 09-19-2007 at 11:46 PM.
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Old 09-20-2007, 12:27 AM   #18
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Quote:
Originally Posted by WickedRydaX View Post
The overlap is a few mm all the way around the edge of the piston that has a flat spot on the head. The thicker HG just moves the flat spot that thickness away from the piston. With the thicker HG you can cool that area down, but still run the risk of hot spots. Hot spots can cause per ign. and kill pistons. Even with your overall CR being 9ish, the outter edge of the piston has a very high CR. I have seen it kill a few pistons, mainly taking out the ring land area of the pistons. I would say you are going to be "safer" using a 2.5 head, but there are many cars that run a 2.5block/2.0heads and make fairly nice power. A buddy of mine, has worked for/with ESX and many other subaru shops, has a 16-17psi rule. He has seen many many 2.5/2.0 go after they push that psi limit. I didn't believe him and ran 18 psi (to get a 400awhp pull) and I killed the engine. I now run a full STi longblock swap, with the AVCS.
MCL
I would think that w/ a good tune you can run 10:1 I have a 2.5/2.0 pushing 22 lbs daily
logged 5k already .... knock on wood she is very very tight . ( Has eaten a few Sti's ) I have personally tuned this car myself w/ open ecu . I believe these bottom ends go a loong way.
Just My .02
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Old 09-20-2007, 01:43 AM   #19
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That "overlap" makes sense. So it probably would be better to use the 2.5 NA heads for that reason.

But what if you were to use the 20G heads. Could you do a little work with a carbide burr and smooth the edges of the overlap to try and eliminate the hot spots? I guess you could CC the combustion chambers and get them exactly matching eachother, and also recalculate CR. Is this even possible?

I do have an extra EJ20G motor that i could take the heads off and try it. This is why I wanted to try and use the 20G heads, because I already have them. I haven't bought the sti short block yet, but I guess i could use the gaskets to see how much overlap were talking about. Also I was planning on about 15 to 17 psi of boost, so this falls within that 16-17 rule you were talking about.
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Old 09-20-2007, 11:43 PM   #20
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Quote:
Originally Posted by sense of nature View Post
I would think that w/ a good tune you can run 10:1 I have a 2.5/2.0 pushing 22 lbs daily
logged 5k already .... knock on wood she is very very tight . ( Has eaten a few Sti's ) I have personally tuned this car myself w/ open ecu . I believe these bottom ends go a loong way.
Just My .02
It is more of a physical issue, not a tune issue. That is just what he has seen happen, and I am starting to believe. I hate to tell you this, but the last guy that told me that same thing you are eat his words within a few weeks. Not saying you will, but he did. He is now doing an insane build to make up for it, so I guess it's not all bad.
morrocco88 I will try to get some photos of a set of 2.0 wrx heads that have been used with a 2.5 STi block tomorrow.
MCL
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Old 09-24-2007, 01:06 AM   #21
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Just checking in to see if you got those pictures. Also looking for a 2.5 na long block with blown head gaskets or something, because my neighbor wants the crank and rods for his 2.2 stroker build, and I could use the heads for this build.
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Old 09-24-2007, 10:13 AM   #22
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Yeah I got them, sorry I forgot the real cam so I had to use my phone.


You can see the black ring around the whole out side edge. I will try to get some better ones on wed if I can remember the cam.
MCL
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Old 09-28-2007, 06:00 PM   #23
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Just aquestion, regarding the Cometic gaskets.
- Do they make them for the EJ20 also?
- Where can i find Cometic gaskets to order online?
Thanks
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Old 09-28-2007, 06:06 PM   #24
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Those thicker gaskets are usually Special order. Call these guys there good:

http://www.jscspeed.com/wrx/wrx_base.html
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Old 09-28-2007, 09:45 PM   #25
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A little better shot of the mis-matched size on the 2.0 heads to 2.5 block.

Here is a pic of a 1.8 head run on a 1.8 engine, I didn't have any 2.0 head from 2.0 blocks. You can see how there isn't nearly the as big of a ring on the outside of the CC in the head like there is in the other photo.
Please don't make fun of my tiny exhause vavles
MCL
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