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 Post subject: The DOHC installation 'unspoken' details thread
PostPosted: Mon Dec 08, 2008 7:11 am 
Fourth Gear
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Lately there is alot of talk about DOHC heads. Either on 22T conversions or complete motor swaps. Everybody likes to say 'the heads bolt up', which is true. However there are alot of details that can make this 'bolt on' conversion a make-or-break proposition for many.

I intend for this thread to be an ongoing databank on DOHC swap information. All are free to contribute, but I ask that you keep it to facts. Please support your facts with proper documentation, such as pictures. Feel free to ask questions, of course.

There are three basic heads that seem to pop up in this forum the most. Legacy EJ20G heads, WRX EJ20G heads, and USDM (non-turbo) EJ25D heads. Early ('94-'98ish) Legacy twin turbo heads (EJ20h) are commonly discussed also, and can be considered the same as Impreza EJ20G heads. EJ20K and late twin turbo heads (Ej20r) are also completely compatable with anything stated in this guide, but because of thier value are rarely chosen by us 'old schoolers'.

This thread also only applies to phase I heads. Phase 2 DOHC heads have a different intake manifold bolt pattern. If your heads have an inline pattern then this guide will apply.
Image

The pros/cons, performance, relability, and uberness of each head design is outside the scope of this thread. This thread is intended to catalog what it takes to install the various heads (as part of an assembled longblock) in a USDM BC/BF Legacy turbo.

This thread assumes you already have your longblock assembled, with cams in and cam covers on. Water and oil pumps each have thier own merits and are beyond the scope of this thread. As long as you have a turbo water pump you'll be fine as far as DOHC head installation goes.

Crankshaft position sensors

Image
Both EJ22 and Legacy EJ20G sensors are the same and plug into the vehicles harness at the rear of the engine. The WRX sensors plug directly into the engine harness. The Legacy twin turbos use the same non-corded sensor as the WRX EJ20G. If your keeping the stock EJ22t wiring, use the corded sensor (stock BC EJ22).

Camshaft position sensors

Image
Again, both EJ22 and Legacy EJ20G sensors are the same and plug into the vehicles harness at the rear of the engine. The WRX sensors plug directly into the engine harness. If your keeping the stock EJ22t wiring, use the corded sensor (stock BC EJ22).

Knock sensors

All early EJ Subaru knock sensors are compatable. Choose the best one you've got.

Rear engine connector bracket

This step mostly applies only if your installing a complete motor and needed to swap the above listed sensors to match your car's harness.

Image

The Legacy bracket is designed to hold three conectors (Cam. crank, knock) while the WRX bracket only hold two (Multi, knock). Use a Legacy bracket for convience.

Basic sensors and bracket installed for installation in a Legacy.
Image


Coolant pipes

The stock EJ22 coolant pipes cannot be used. They simply will not fit on/around the DOHC heads.

Image
Legacy EJ20Gs and WRX EJ20Gs use the same coolant pipes. I do not have a set of EJ25D pipes to add to the photos, so at this point I do not know if they are the same as EJ20G pipes.

EJ20G coolant pipes installed on Legacy EJ20G.
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Legacy twin turbo coolant pipe are routed very differently from other engines to avoid the second turbo.
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Coolant crossover pipe

The main difference between the crossovers is the location of the two temp sensors.

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EJ22s have the sensors on the opposite side as EJ20Gs. The engine harness for each version matches the crossover, of course. The WRX version also eliminated an insignificant casting 'bump'. I do not have an EJ25D crossover to add for comparision.

Image
The Legacy twin turbo crossover has the sensors on the same side of the engine as the EJ20Gs, but they are located on the front side instead of the back. The contour of the pipe is also designed for the under-the-manifold turbo inlet.

The most often given advice is to use the EJ22T engine harness on your DOHC engine to make it plug-n-play. This is sound advice and will work, but there are a few things to look out for.

If your planning on using an EJ25D intake manifold you cannot use the EJ22T crossover. It interfears on the temp sensors.
Image

If you plan on using an EJ20G intake manifold the clearance with the idle air pipe (to plug in the sensors) is very tight with the EJ22T crossover.
Image

So, that leaves using the EJ20G crossover. Of course, that means modding the EJ22T engine harness to extend the temp sensor wires to the other side.

I hope to add info on EJ25D and twin turbo crossovers soon.

Oil pan and Dipstick

All the oil pans are the same as far as functional differences. While the dipsticks have a similier shapes the mounting tab prevents EJ20G and EJ22 from being interchangable.
Image
Both Legacy EJ20G and WRX EJ20G dipsticks are the same. I can't confirm (yet) but I'm sure that EJ25D dipsticks are also the same.

Image

Timing belt tensioner bracket

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Other than a few casting differences, both styles of EJ20G bracket are the same. The EJ22 bracket does not have the 'ear' needed to secure the DOHC timing cover. The EJ22 bracket can be used with the DOHC covers, but may introduce a vibration or fatigue point.

Somewhere around '98-'99 Subaru redesigned the tensioner device. If you use the bracket and tensioner you can upgrade to the new style. Make sure you get one from a DOHC motor (such as the USMD WRX) so it has the 'ear' to secure the inner timing cover.
Image

Inner timing covers

Left covers

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Image
The WRX EJ20G, twin turbo, and EJ25D covers are the same and will not fit the Legacy EJ20G heads. The Legacy EJ20G cover will not fit WRX, twin turbo, or EJ25D heads.

Image

Right covers

Image

Other than minor casting updates, all are the same.

Image

Timing sprockets

Image
Other than a few casting differences, crank timing wheels are all the same.

Image
Image
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All cam wheels are all interchangable. Legacy EJ20G ones are metal, while WRX EJ20G, EJ25D, and Twin turbo sprockets are identical to each other and plastic.


Timing idlers

All the other idlers and tensioners are the same between all models. EJ22, EJ20G, twin turbo, and EJ25D.
Image

Timing Belt

Obviously you can't use an EJ22 belt. Both Legacy EJ20G and WRX EJ20G use the same timing belt. Numerous posts indicate that the EJ25D belt is also the same.
Image

Timing tensioner

Once again, all models are the same. Unless your upgrading to the newer style.
Image
Image

Outer timing covers

Broken record, but, other than a few casting differences all the same. Some say Turbo!! For the center cover, the SOHC and DOHC covers are even the same.
Image
Image



Next installment....intake manifold choices.

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'93 Pure White SS EJ20G slanty intercooled, SIDESWIPED! In stasis.
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Last edited by PhyrraM on Mon Apr 20, 2009 6:55 am, edited 14 times in total.

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PostPosted: Mon Dec 08, 2008 7:24 am 
Fifth Gear
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I don't have pics to add at the moment since I'm 60 miles from my garage, but the '98 EJ25D in my garage has the newer style timing belt tensioner. Maybe they made a switch somewhere in there like Subaru is known for?



Good thread though. I'll dig into my pile of stuff this upcoming weekend and see if I can add anything else.

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PostPosted: Mon Dec 08, 2008 7:32 am 
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Yeah Subaru updated the tensioner somewhere along the line. It's my understanding that you can use either as long as you use the proper bracket to go with it.

I personally can't confirm, but I will add it to the thread as soon as somebody can. I'll head out to the junkyard to grab a few samples, eventually.

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PostPosted: Mon Dec 08, 2008 7:40 am 
Fifth Gear
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^Word. Subaru seems to like to make changes whenever they run out of stock, lol. Like my buddies '04 Impreza that has '05 headlights.




Once I have more content, I'll document my experience with fitting the 25D heads in the process of my swap into a new shell. I like the idea of this thread though. Very stickyable.

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PostPosted: Mon Dec 08, 2008 4:43 pm 
Fifth Gear
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I think you labeled one of your pictures incorrectly.

EJ22T would be SOHC but that sure looks like a DOHC timing belt backing.

Image


Here's a picture I had of my EJ20H twin turbo crossover. The temp sensors are on the front of the crossover pipe not in the rear.

I can get a better picture of it if you'd like.


Image



Thanks for the writeup! Very informative. Nicely done.

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PostPosted: Mon Dec 08, 2008 5:50 pm 
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Good catch, I'll fix the pic ASAP. It should have been labeled Legacy EJ20G.

I'll add the twin turbo crossover info to that section.

Thanks!

...and fixed. :smt023

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PostPosted: Tue Dec 09, 2008 3:32 am 
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Image

Minor nitpick, but I think the middle one should be labeled "Legacy EJ20G".

The EJ22T coolant pipe that bolts to the block can be used with the Legacy 20G heads (on the left in your pic). As you stated, the other EJ22T coolant pipe cannot.

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PostPosted: Tue Dec 09, 2008 8:08 am 
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More updates and fixes. Thanks to Kimokalihi for the EJ20H twin turbo pics.

Keep the info flowing, we'll turn the DOHC conversion into a 'bolt-on' yet.

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PostPosted: Tue Dec 09, 2008 10:48 am 
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What year of 25D heads are you using for a comparison? I think they may be slightly year sensitive. My buddy is using the 25D heads and intake with a 22T crossover without issue.


I need to get my motor out and heads on for more comparison. We'll get this ironed out one way or another.

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PostPosted: Tue Dec 09, 2008 3:39 pm 
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93forestpearl wrote:
What year of 25D heads are you using for a comparison? I think they may be slightly year sensitive. My buddy is using the 25D heads and intake with a 22T crossover without issue.


I believe that the ones I have for comparision are from a '98 RS. The crossover has more to do with what intake manifold you choose than the heads themselves.

So far it seems that as long as you have the proper timing covers, the major obsticles to installing DOHC heads are in the intake manifold. Particularly if you don't have an entire motor to source all the unique hoses and pipes.

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'93 Pure White SS EJ20G slanty intercooled, SIDESWIPED! In stasis.
'94 FWD and '95 AWD Laguna Blue SVXs.
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PostPosted: Wed Dec 10, 2008 5:15 am 
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There should really be info in here about how the ej25D heads need to be modified for use in a turbo car. Mine are off my car atm, so I'll try to grab some pics.

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PostPosted: Wed Dec 10, 2008 5:31 am 
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Grayguy wrote:
There should really be info in here about how the ej25D heads need to be modified for use in a turbo car. Mine are off my car atm, so I'll try to grab some pics.


It's coming. I was planning on that after some manifold discussion.

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'93 Pure White SS EJ20G slanty intercooled, SIDESWIPED! In stasis.
'94 FWD and '95 AWD Laguna Blue SVXs.
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PostPosted: Mon Dec 22, 2008 1:55 am 
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Ok, time for some updates. This time around I will start with a few observations regarding trying to use the EJ25D intake manifold.

Once again, any and all comment sare welcome so the thread can be as accurate as possible. I'm hoping that those in the future will be able to use this thread as a sort of shopping list to make a DOHC install as painless as possible.

EJ25D Intake manifolds


Here you can see that the EJ22t and the EJ25D have basically the same layout. The IAC valve, PCV valve, vacuum port for the brake booster, and coil mount are all in the same place. The EJ25D has EGR, but for installation in a BC Legacy will most likely be removed and capped.
Image

The big question at this point is...Will the major components fit with an EJ25D intake manifold?

Yes, they will. With a few caveats, of course. First, use your EJ22T throttlebody.
Image
The EJ22T water passage has a 90 degree fitting that gives the turbo outlet more room. Also, the EJ25D TPS is not correct for an EJ22T harness.

Image

Second, use your EJ22T IAC valve. It has the air inlet pipe rising up over the manifold. With the EJ22T IAC valve you can use the stock hoses and resonator (or coffee cup mod).
Image
Image

Next question...Will a turbo with the 90 degree inlet fit?

Yes.

Image
Image

From this point, it's a simple matter to finish the rest of the intake tract using stock EJ22T parts.
Image
Image

The bypass valve in the photos above is an EJ20G setup. It's the same valve as the EJ22T just used in a different location. The turbo charger outlet pipe in the pictures is a Legacy EJ20G (air-to-water), but all EJ20G intercoolers have the same style elbow and BPV nipple.

All EJ20G styles of intercoolers are a bolt on at this point.
Image
Image

Image
Image


Notice...I have not addressed PCV, vacuum or water lines yet. If your doing a catch-can the PCV should be a non-issue. Vacuum lines are usually not too big of a deal if you have to run all new ones.

Update: I have tried many different subaru PCV hoses in an attempt to find something that works well. My conclusion is that if you wish to use an EJ25D intake manifold (instead of EJ20G) you should use a catch can setup instead of a traditional PCV system. The proper hoses for this swap either don't exsist or ar very uncommon. A catch can setup Is a huge upgrade from the factory PCV, but doesn't "look" stock.

Water lines, however, can be a big deal. there is no mounting point for a normal Subaru turbo expansion tank. And room in that part of the engine is very tight with this manifold.

More to come.

_________________
'93 Winestone SS Auto, '91 Pearl White SS.
'93 Pure White SS EJ20G slanty intercooled, SIDESWIPED! In stasis.
'94 FWD and '95 AWD Laguna Blue SVXs.
2017 Pure Red BRZ Limited w/Performance pack


Last edited by PhyrraM on Fri Apr 17, 2009 6:04 am, edited 2 times in total.

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PostPosted: Tue Dec 23, 2008 2:53 am 
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I have stickied this thread for the short term. Long term I expect it to be worthwhile to put it into the compilation thread.

Nice work so far.

I will address the questions about the EJ25D heads. There are two versions. The '96 heads were HLA's under buckets, just like WRX Ej20G heads from '93-96.

Starting in '97 the Ej25D went to shim over bucket (like the Ej20K, more on that in a minute :wink: ). That was the only major change in the heads, but it did mandate a change in cams and valves as well. You need to know what year head you own if you are shopping for replacement parts.

The new style timing belt tensioner was not introduced until 1999. '99 was a weird year because the 2.5RS got the SOHC Ej25 heads, but the Legacy GT, Outback and Forester EJ25's kept the DOHC heads for one more year. Subaru had produced so many of those heads that they had to try and use them up. For years you could actually buy brand new ready built EJ25D heads from the dealership as "rebuilt exchange" heads. They weren't rebuilt. They were new and cost something like $300 a pair if you handed them a junkyard set of heads. Some smaller more obscure dealerships could still have some of these sitting around. But if you've got a new style tensioner on your core engine it's a '99 or has had a timing belt job and got updated at that time.

So, there are two heads missing from this list. The first is the EJ20K. DOHC WRX heads from '97-98. Shim over bucket except for STi which are shim under bucket.

The other is the later Ej20 twin turbo heads. I would have to double check, but I think that the change year was 1998 and that they were also used in 1999. For purposes of this project you can treat them just like EJ20K heads, which are very very similar to late Ej25d heads.

There were a couple of other things I noticed on my pass through but I will have to go re-read it to catch them. Sorry, I don't have any pictures. I don't have any of these heads in my garage right now. Hopefully I've earned the right to be taken at my word around here. If not, I'll just remove my posts...

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PostPosted: Tue Dec 23, 2008 2:59 am 
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Oh yeah. IAC, coolant tank and water flow. If you are using Ej20G heads from a WRX, try to get the manifold complete with IAC and coolant lines. If you have all those parts, then it's very very easy to install the water tank on the driver's side, all the hoses route properly, as do the black hard lines that feed the tank and the TB and IAC.

Bottom line is that if you are using an intercooler, I have found the EJ20G WRX manifold and all it's accessories and plumbing to be the easiest to use as a "stock" replacement. As has been described, the twin turbo and NA have lots of little PITA modifications. I once made an Ej22T coolant tank and hard lines work on some Legacy EJ20G heads. It's wasn't terribly easy or pleasant.

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1973 Porsche 914 2.0 l -Suby swap pending
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PostPosted: Tue Dec 23, 2008 3:18 am 
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Thanks Matt. Yes, your word counts for volumes. Much of my knowledge comes from various posts of yours, on numerous forums. Pics are always helpful because the chances of keeping it to facts is much increased.

I was planning on addressing the types of heads in more detail later, but for now I am trying to concentrate on installation. I believe, other than the plugging of the secondary ports on twin turbos, that all of the phase 1 DOHC heads are the same (installation wise) from the manifold up. And from the manifold down, only the Legacy EJ20G needs attention, as the up-pipe support and the right inner timing cover are not compatable with WRX EJ20G and later heads.

My goal is to outline for posterity the details needed to get any of these heads into our USDM BC/BFs with the least amount of fabricating possible. Ideally every DOHC conversion would involve a complete core engine for 'the small parts'. But we know that sometime that doesn't happen. :wink:

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PostPosted: Tue Dec 23, 2008 11:51 am 
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Up until this thread I was under the impression that the SOHC heads had less valves but I guess they have the same amount as the DOHC? So what are the advantages of using DOHC heads? Is it just larger ports and better flow?

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PostPosted: Tue Dec 23, 2008 2:53 pm 
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kimokalihi wrote:
Is it just larger ports and better flow?


Pretty much, yes. In something like an inline 4 there's definite advantages to a DOHC design. With the Flat 4 it's not as pronounced and given that one cam handles on 2 cylinders on each side, a DOHC is almost redundant.

It really is a shame that the SOHC Ej25 heads interfere with the stock turbo exhaust plumbing because they would be another great option since they flow so damned well. Sure there are ways to make them work (especially with a rotated mount kit) but that's for another thread. I don't really want to take this thread off it's point.

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PostPosted: Tue Dec 23, 2008 3:10 pm 
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Great job guys. This thread will be handy for many people.

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PostPosted: Wed Dec 24, 2008 1:17 am 
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I took a look at the Ej25D languishing in the corner of my shop today. It's got a coolant pipe like an Ej20G with the pair of sensors located on the right rear. Treat it the same way. Is there any other information we need off this engine?

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PostPosted: Wed Dec 24, 2008 3:26 am 
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Matt Monson wrote:
I took a look at the Ej25D languishing in the corner of my shop today. It's got a coolant pipe like an Ej20G with the pair of sensors located on the right rear. Treat it the same way. Is there any other information we need off this engine?


Thanks. I'll add that to the crossover pipe section.

Can you verify the dipstick is the same part (or at least compatable) as an EJ20G and/or EJ20K/H/R? I'm running with the assumption that all the DOHC dipsticks are the same and all attatch to the same bolt on top of the left head.

I'm going to have to hit up the junkyard after Xmas, I want to get some hands-on with the EJ25D PVC hoses and coolant pipes (from the waterpump up and over the block). I'm thinking (hoping) that they just might be the same as an EJ20G (minus the second pipe that follows the crossover and feeds the turbo).

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'94 FWD and '95 AWD Laguna Blue SVXs.
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PostPosted: Wed Dec 24, 2008 4:14 am 
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PhyrraM wrote:

I'm going to have to hit up the junkyard after Xmas, I want to get some hands-on with the EJ25D PVC hoses and coolant pipes (from the waterpump up and over the block). I'm thinking (hoping) that they just might be the same as an EJ20G (minus the second pipe that follows the crossover and feeds the turbo).


I wouldn't bother. The NA stuff is way different. It's got fewer bungs on the water pump for both black lines and the oil cooler that are not present. The lines run totally differently because the EJ20G has the IAC on the left and the Ej25D has is on the right like an Ej22. I suspect that they are the same as an Ej22E. I can check for you.

I do happen to have all of the black lines for every engine in question. Of course, only some of them are actually marked so it would take a little detective work on my part but I think I can sort it out.

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1974 Porsche 914 Cam Am Limted Edition AKA the Bumble Bee
1973 Porsche 914 2.0 l -Suby swap pending
1968 Porsche 911t survivor 47k original miles
2000 2.5RS daily driver.
1999 2.5RS w/ 50+ extra whp
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PostPosted: Sun Dec 28, 2008 8:56 am 
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Location: Western WA!
Can you add a section about replacement parts interchangeability? It'd hard to get JDM stuff, so it would be helpful to know what can be replaced with USDM parts. Specifically, I'm thinking valve cover gaskets are worth including.

I'm looking for the USDM equivalent to Legacy EJ20G valve cover gaskets. Info I've found so far claims that '96 Legacy GT gaskets will work, but I've yet to see pictures.

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PostPosted: Sun Dec 28, 2008 9:19 am 
Fifth Gear
Joined: Sun Nov 23, 2003 12:22 am
Posts: 2774
Location: Western WA!
Here are pics of Legacy EJ20G valve covers:

Image

Image

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PostPosted: Sun Dec 28, 2008 11:20 am 
Fourth Gear
Joined: Thu Aug 11, 2005 4:34 pm
Posts: 1980
Location: Lake Elsinore, CA
Legacy EJ20G heads do not have a USDM equivalent. There are relable Ebay suppliers that can souce almost all service items. I will try and add a few examples later.

WRX EJ20G and early twin turbo Legacy (EJ20H) heads are basically the same as '96 USDM EJ25D heads.

WRX EJ20K and later twin turbo Legacy (EJ20R) heads are basically the same as '97+ EJ25D heads.

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