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Old 03-15-2006, 09:34 AM   #1
readymix
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Default AVCS Heads on Non-AVCS blocks.

I've done a little searching and come up with some things of interest. But I figured some more discussion might be a good thing. Especially for the expanding market of EJ20 WRX owners that would like to do franken-motors with AVCS heads but still utilize their stock ECU (for ECUTek or ProTune)



http://forums.nasioc.com/forums/show...ght=AVCS+Heads <--Cam Retainer thoughts (DON'T DO THIS!!!)

http://www.elementtuning.com/V8%20In...%20Install.htm <--Phil at Element Tuning talks about modding JDM Forester heads

http://forums.nasioc.com/forums/show...ght=AVCS+Heads <--More AVCS on NON-AVCS ecu talk.
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Last edited by readymix; 03-15-2006 at 09:59 AM.
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Old 03-15-2006, 09:45 AM   #2
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i think this is a great topic for this area. it should be a sticky. the info on elements site is good. thanks for posting that.
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Old 03-15-2006, 09:46 AM   #3
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For the first thread dont even think of trying that. Those caps are are cast, line honed and numbered for the each head they make. No cam caps are interchangiable period.
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Old 03-15-2006, 09:59 AM   #4
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I'll still leave the first link up there for information purposes only, but that is good information to know. I was unaware of the need to use the caps that come with the heads.
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Old 03-15-2006, 11:36 AM   #5
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Just keep in mind the following to keep a swap simple without much custom wiring etc.
- whatever heads you use you also use the ECU that was used with them from the factory.
-2.0L heads are fine to use with a 2.5L (larger bore block)
-I would not suggest to do the opposite (2.5L larger chamber heads used on a 2.0L block)
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Old 03-15-2006, 11:58 AM   #6
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That is good information, no doubt. But I don't mind custom wiring I guess...not that there should be much custom wiring involved. Just a relocation of the WRX CAM sensor onto the AVCS heads. The idea here is to avoid rewiring your car or using a standalone.

Another question, why no 2.5L heads on smaller shortblocks? I have an EJ22T shortblock. What would be the pros/cons of using AVCS heads on an EJ22T block?
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Old 03-15-2006, 12:17 PM   #7
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If you put a 2.5L (ex. usdm STI head) on a smaller than 99.5mm block then your combustion chamber would overall be larger than your cylinder, which could have negative eggects. The chamber size on the USDM STI heads are 99mm and the bore of that engine is 99.5mm, this was done for a reason.

Also I just put a USDM STI headgasket up to a EJ207 block and the head gaskets surface that seals on the top of the cylinder would barely seal, I would not trust it.

Although using a 2.2L block which has a bore size in between the USDM STI and the 2.0L you might be able to get away with it.

So my question to you is what is your pro for using a 2.2L block vs a STI block?
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Old 03-15-2006, 01:24 PM   #8
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Availability (I have an EJ22T, I do not have an STi shortblock). That is my pro. That and it's a closed deck EJ22. Why not use it?
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Old 03-15-2006, 02:00 PM   #9
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The 2.5 heads possibly could be used.. I just have never done it. Not the most ideal. I would use 2.0L heads for an application like that. It is proven, makes more sense.
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Old 03-15-2006, 02:58 PM   #10
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Some things:

1) The heads will be larger than the combustion chamber bore. Correct?
Is this something that has a known correction? And what could be a possible problem caused by this?

2) If it will work, what would be some cons to using these heads on a 2.2L

3) What differences are there between the 2.5L N/A heads and 2.5L AVCS in regards to this situation. For example, I know the old popular setup was an EJ22T with 2.5LN/A heads because they flowed better. Is the bore of the 2.5N/A different than the STi/ForesterXT/LegacyGT? <--I guess I could search that. If the bores are the same, why wouldn't this be a reliable setup?
Some information of note

EJ22T

bore = 96.9

Stroke = 75mm
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Old 03-15-2006, 03:04 PM   #11
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I went ahead and looked it up

The EJ25 and EJ257 (2.5N/A and STi respectively) are both a 99.5mm bore and 79mm stroke.

I'll reiterate what I mentioned previous post, people chose the 2.5L N/A heads over EJ22T heads because they out flowed them. This was 'commonplace' and I believe there might still be some people using this setup.

Then my question:

If EJ22T + EJ25NA heads = good - then
EJ22T + EJ257 heads = good?

We are talking about a head that is made for a shortblock that has the same bore and stroke. That is why I am confused as to why this would be a bad idea.
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Old 03-15-2006, 03:05 PM   #12
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BTW, after reading my above posts, I sound 'knowledgable' and 'pushy' and I don't wish to come off as such...I'm dumb when it comes to this stuff so I'm asking questions. Please don't be put off or think I am being snippy
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Old 03-15-2006, 05:41 PM   #13
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EJ25 and EJ257 either way the combustion chamber will be the same side 99mm, I agree that does not matter.
When I respond to someones post I never suggest or agree with something that I would not do for my own personal car. If I personally dont feel comfortable I will let you know.

Con= the smaller bore disrupting the airflow, burn properties etc. (doesnt take advantage of the tight quench area, and subarus pentroof head design)

This possibly can be done if the head gasket has enough seating area, a build like this would not be at 100% of its potential, I believe this build could def. make more power with a 99.5mm+ bottom end.


Now this would not be the easiest nor cost effective, but if I had no other choice, a fix would be the following.
$$$
-Weld in material into the combustion chamber (the round sides of the combustion chambers)
so you can bring the combustion chamber size back down to your bore size.
(be sure not to keep much material around or close to the valves as you do not want to shroud the valves more subaru already has them shrouded)
-you are trying to make up for approx. 2mm
-by the way good deep welds will not have any problem with combustion chamber heat.
-after welding taper the welded material so id blends into the chamber itself.
-cc each chamber and match to the largest volume.
$$$

After doing this I would agree there would be no con to this build.

Last edited by 02Toyowrx; 03-15-2006 at 06:53 PM.
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Old 03-15-2006, 07:01 PM   #14
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That sounds expensive. Very expensive.

Anyone with an EJ22T+EJ25 N/A DOHC heads setup wish to comment?
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Old 03-15-2006, 07:14 PM   #15
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Anybody have some instructions on how to prepare a AVCS head for non-AVCS use??? ie: what needs to be sealed, taken off, tapped, ect....
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Old 03-15-2006, 07:33 PM   #16
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It's in one of the links above.

As for the AVCS sealing etc...
I'm talking with a pair of local Subaru dealership service guys. The idea was brought up today about getting the attachment for the oil cooler that sandwiches between teh filter and the block, then running lines to the AVCS/CAM lubricators. You still need to lube the cams.
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Old 03-15-2006, 09:17 PM   #17
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I do believe that...

1. You can use EJ25 heads on smaller blocks that are turbo. People don't care about quench, or flame front, or any of the fancy n/a talk. It's compressed to no end and then it explodes with the spark.

The EJ22'ers like to use the EJ25 head because it drops the compression even lower than stock.

from what I understand, EJ20 heads although being a different bore for the chamber, have the same amount of combustion chamber cc's as (general) EJ25 heads. ~49cc the last time I checked any sources. (this would be the EJ207 head for comparison reasons) So persons for whatever reason don't want to move to EJ25 heads, could try to get their hands on EJ207 heads.
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Old 03-15-2006, 09:22 PM   #18
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Quote:
Originally Posted by Peeblesmx445
Anybody have some instructions on how to prepare a AVCS head for non-AVCS use??? ie: what needs to be sealed, taken off, tapped, ect....

What heads? some would work others would not
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Old 03-15-2006, 10:56 PM   #19
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jdm v7 spec c big port heads... can they be used without AVCS functioning?
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Old 03-16-2006, 12:19 AM   #20
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Quote:
Originally Posted by bikerboy
What heads? some would work others would not
JDM V7 'Big Port" heads
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Old 03-16-2006, 12:24 AM   #21
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Or how about 2004 ForesterXT heads
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Old 03-16-2006, 10:12 AM   #22
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Most of the AVCS heads will bolt up but you may need to purchase the AVCS oil lines if your heads do not come with them. There is no blocking of the AVCS oil solenoids. This is a misconception and will damage the heads if blocked since they oil the front cam journal. You can block the cam shaft itself but what's the point? You can run the heads as they are and just have the AVCS solenoids non-functional. You won't have the low end power the AVCS system provides but top-end power will be identical.
If you're not going to use the AVCS system then you are better off purchasing cams for the standard heads. You'll likely have more compression and an overall increase in flow. I've tuned cars with 2.5 short blocks using WRX heads with Kelford cams and they make big power with excellent spool up. If you run a Hydra EMS then getting the AVCS heads to work is a piece of cake and the AVCS heads are the way to go. I'm not giving up my AVCS for anything!

If you are using US spec STI heads you'll have to mount your cam sprocket sensor and possibly purchase a different cam sprocket (depending on the pickups).

Thanks,
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Old 03-16-2006, 10:21 AM   #23
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Thanks for the reply, good info.
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Old 03-16-2006, 03:43 PM   #24
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Quote:
Originally Posted by JonofScio
I do believe that...

1. You can use EJ25 heads on smaller blocks that are turbo. People don't care about quench, or flame front, or any of the fancy n/a talk. It's compressed to no end and then it explodes with the spark.

The EJ22'ers like to use the EJ25 head because it drops the compression even lower than stock.

from what I understand, EJ20 heads although being a different bore for the chamber, have the same amount of combustion chamber cc's as (general) EJ25 heads. ~49cc the last time I checked any sources. (this would be the EJ207 head for comparison reasons) So persons for whatever reason don't want to move to EJ25 heads, could try to get their hands on EJ207 heads.

That is why you are waiting for a new engine.
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Old 03-17-2006, 01:56 PM   #25
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dude, are you going to get back to me on that gauge 02toyowrx? wondering if you are going to reply to my pm's

--- sorry for getting off topic, but i'm trying to do business with this guy...
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