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Old 07-17-2005, 04:13 PM   #1
EastsideLegacy
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Default 98 dohc heads on sohc block

Just wondering if i could buy a 2001 sohc block and interchange my old 98 heads
to the new block and will it all bolt up nicley...


thanx main
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Old 07-17-2005, 04:14 PM   #2
Russell Rogers
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Everything will bolt up f\ine. You will have to use sohc crank, pistons, rods, rings. But the heads will bolt up fine. All the headgaskets are the same also.
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Old 07-17-2005, 04:17 PM   #3
pilfflip
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That Really Depends On Which Engines You Are Talking About Most Of Them Will Bolt Up Properly But That Doesn't Necessarily Mean That The Coolant Passages Will Match Up, We Need More Info. What Engine Are Talking About An Ej 2.2? Or The 2.5? Why Do You Want To Get A '98 Block?



~mike


WHAT RUSSELL SAID TOO
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Old 07-17-2005, 04:21 PM   #4
EastsideLegacy
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I want a 2002 block with low miles and bolt up the 98 heads to it. also it's a 2.5..... any other input will help thanx for the response's....

thanx main
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Old 07-17-2005, 04:46 PM   #5
Russell Rogers
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I know the 2000 and 2001 will be fine. I have no idea about the 2002. why don't you just get a dohc block though. You won't gain any power with a sohc block. ANy power gains would be found in a sohc motor or a dohc block with sohc heads.
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Old 07-17-2005, 04:53 PM   #6
EastsideLegacy
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Its just easier to find a low milage block from a 01 or 02 than from a 98.
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Old 07-17-2005, 05:01 PM   #7
Russell Rogers
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oh i see. Well you need to get the whole bottom end in rderf for it to work. crank pistons rods rings oil pan etc. Price wise its alot. I know i have a sohc block sitting in my garage. All the stuuf that goes with it is where the price kills ya.
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Old 07-17-2005, 05:24 PM   #8
Jonathan
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I *think* this dude is experiancing problems with his '98 Legacy's motor and is maybe looking at a cheap way to get back in business with a Phase II motor.

The short answer from what I have been told is that you can bolt on your DOHC heads, intake and exhaust manifold to the newer motor. This way you dont have to swap ECU or worry about MAP vs. MAF sensors. However in doing this you will need to use Premimum Gasoline with the new motor.
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Old 07-18-2005, 12:07 AM   #9
ooberdoob
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Quote:
Originally Posted by Jonathan
I *think* this dude is experiancing problems with his '98 Legacy's motor and is maybe looking at a cheap way to get back in business with a Phase II motor.

The short answer from what I have been told is that you can bolt on your DOHC heads, intake and exhaust manifold to the newer motor. This way you dont have to swap ECU or worry about MAP vs. MAF sensors. However in doing this you will need to use Premimum Gasoline with the new motor.
i presume doing so will cause the compression ratio to go ballistic hence the premium need?
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Old 07-18-2005, 01:29 AM   #10
Russell Rogers
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compression will be the same. the blocks are exactly the same the only difference is cutouts for the difference in piston versus rod.
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Old 07-18-2005, 06:00 AM   #11
Patrick Olsen
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Quote:
Originally Posted by Russell Rogers
compression will be the same. the blocks are exactly the same the only difference is cutouts for the difference in piston versus rod.
The blocks aren't exactly the same, and the blocks don't determine compression ratio, anyway. Compression will most definitely not be the same with DOHC heads on a Phase II block. I think it's safe to assume when Eastsidelegacy asked about getting a low mileage block, he meant a short block. There would be no point in him buying a newer block just to throw his high mileage '98 rotating assembly into it, and I think it's safe to assume he's smart enough to realize that.

So, with that said, yes, putting DOHC heads on a Phase II short block will result in a higher CR. Based on some numbers gathered by my buddy, wac ( http://wac.addr.com/auto/obs/turbo/ejcalcs.html ), the DOHC heads have a smaller combustion chamber, while the Phase II engine has smaller cutouts in the piston. Combine those two and you get a higher CR. Using the thicker DOHC head gasket will help keep the CR from being too high. Using wac's numbers I get 11.9:1 using the SOHC gasket ( ) and 10.6:1 using the DOHC gasket.

Pat Olsen
'97 Legacy 2.5GT sedan
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Old 07-18-2005, 04:09 PM   #12
Huffer
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This is spooky.
I'm picking up a used 99RS shortblock on the weekend, to match up to my Legacy's EJ25.

Will I have any comp. issues to be wary of with the 99RS block? I'm not sure if it's Phase I or II. Any idea?
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Old 07-18-2005, 10:39 PM   #13
EastsideLegacy
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Quote:
Originally Posted by Patrick Olsen
The blocks aren't . I think it's safe to assume when Eastsidelegacy asked about getting a low mileage block, he meant a short block. There would be no point in him buying a newer block just to throw his high mileage '98 rotating assembly into it, and I think it's safe to assume he's smart enough to realize that.
Your exactly right ... thanx everyone for the info... and im not planning on doing any of this, it's mostly out of curiosity....

yey yea

thanx main
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Old 07-19-2005, 04:23 AM   #14
Chi_San
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Does this mean it's possible to use a different headgasket and increase the CR, if you're talking sohc block and head?
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Old 07-19-2005, 05:05 AM   #15
Jonathan
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Quote:
Originally Posted by Huffer
This is spooky.
I'm picking up a used 99RS shortblock on the weekend, to match up to my Legacy's EJ25.

Will I have any comp. issues to be wary of with the 99RS block? I'm not sure if it's Phase I or II. Any idea?
My understanding is that Subaru converted all Japanese built EJ25 cars from the Phase I to the Phase II block in 1999. As the North American Legacys are built in Indiana, they continued to use the remaining stock of Phase I engine blocks for US built Legacys through out the 1999 model year, although rumour has it that SOMETIME after ~ April 1999 they ran out of Phase I EJ25 blocks, and started using a "hybrid" Phase II block with DOHC heads and Phase I internal engine components for their remaining 1999 USDM Legacys. Jack (GTBGUY) I beleive was able to identify his '99 Legacy GT as being one of the fortunate few "hybid" engined cars.

Short answer to your 99RS short block question is that it is indeed almost 100% certainly a Phase II engine with SOHC heads, although it SHOULD be fairly easy to verify simply by looking at the Cams. Also since you do indeed have an engine in front of you, maybe you could compare it with your Legacy engine and photograph any obvious casting differences ?

At one point several years ago someone claimed that there were different markings on the engine block that designated Phase II vs. Phase I castings. Never having actually been shown where and what to look for, I am at a loss to explain how to spot the different blocks, and can only really look at the different intakes.

Last edited by Jonathan; 07-19-2005 at 05:10 AM.
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Old 07-19-2005, 10:41 AM   #16
Huffer
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Ok, thanks for that info Jonathan, I'll be taking plenty of pics of the block etc. At this stage my Legacy is still running ok, so I have plenty of time to assemble things.

Pat, if you read this, I was checking out the link you posted http://wac.addr.com/auto/obs/turbo/ejcalcs.html , and I noticed that that first table has the 98 Legacy DOHC EJ25 as 9.7:1 compression ratio.
I had an email from Subaru America telling me that the compression ratio on my Legacy is 10.2:1. This is also the ratio that TWE have listed as their stock piston replacement (you might want to let your friend know).
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Old 07-19-2005, 02:03 PM   #17
Patrick Olsen
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Quote:
Originally Posted by Huffer
Pat, if you read this, I was checking out the link you posted http://wac.addr.com/auto/obs/turbo/ejcalcs.html , and I noticed that that first table has the 98 Legacy DOHC EJ25 as 9.7:1 compression ratio.
I had an email from Subaru America telling me that the compression ratio on my Legacy is 10.2:1. This is also the ratio that TWE have listed as their stock piston replacement (you might want to let your friend know).
Well, according to the Service Manual I downloaded, it has a 9.5:1 CR. Granted, that was in the '97 Manual, but as far as anyone knows nothing changed with the 2.5GT engines from '97 to '99, so the '98 should be the same. Strange.

Pat
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Old 07-20-2005, 12:06 AM   #18
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So...bottom of the line is don't plan on putting any kind of forced induction on that frankenstien engine unless you like your motors in pieces...while in your car


~Mike
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Old 07-20-2005, 03:55 AM   #19
Chi_San
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Quote:
Originally Posted by pilfflip
So...bottom of the line is don't plan on putting any kind of forced induction on that frankenstien engine unless you like your motors in pieces...while in your car


~Mike
If he does plan on going that route... Video please.
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Old 07-20-2005, 07:16 AM   #20
Jonathan
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Quote:
Originally Posted by pilfflip
...bottom of the line is don't plan on putting any kind of forced induction on that frankenstien engine unless you like your motors in pieces..
My understanding is that Subaru has finally got the headgasket problem more or less licked. The new headgasket fix invovles a fairly thick metal core gasket that if not bullit proof, has (so far) a reasonable reputation for not sprouting leaks.
Combine this with the newer Phase II block that isn't as prone to flexing and you should have a fairly tight package that should be up to handling as much as 8-10 PSI with proper engine management.

All we need now is someone with lots of youthfull enthusiasm, a few bucks,, and the hours to actually go ahead and do a turbo.

Anyone left ?
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Old 07-20-2005, 10:42 AM   #21
Huffer
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I'm staying allmotor. I've never liked having to deal with boost in corners, and the lack of response irritates me. :shrug:
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Old 07-26-2005, 05:13 PM   #22
Huffer
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Quote:
Originally Posted by Patrick Olsen
Well, according to the Service Manual I downloaded, it has a 9.5:1 CR. Granted, that was in the '97 Manual, but as far as anyone knows nothing changed with the 2.5GT engines from '97 to '99, so the '98 should be the same. Strange.

Pat
Ok, I got the official word from Subaru America on this one.

Quote:
Thank you for visiting the Subaru Web site and for your support of Subaru
products! We appreciate you taking the time to contact us.

The compression ratio for your 1998 Legacy 2.5GT is 9.7 : 1.

I hope this information is helpful to you, but should you have additional
questions or concerns, please let me know and I'll do my best to assist you further.

Best Wishes,

Natalie Cox
Subaru of America, Inc.
Customer/Dealer Services Department
I also have some pics of my 99RS SOHC block that will be mating up to my 98 GT DOHC heads.



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Old 08-06-2005, 01:40 PM   #23
Charlie-III
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IIRC, the outside visible difference of a phase-1 vs phase-2 was the number of bumps on the block by the "EJ" stamping behind the power steering pump.

I know I found it on here at one point.
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Old 08-08-2005, 11:48 AM   #24
Huffer
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Slightly cleaner and more presentable:
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Old 02-25-2006, 03:47 PM   #25
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hey did you ever get your project finished? how did it go. i'm sorta doing the sme thing.. wondered if you ran into any issues?

thanks

-ben
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