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Old 07-03-2004, 02:03 AM   #1
RyansJDMgc8
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Question Can 2.5 SOHC heads fit a US ej20 shortblock?

I have a 2001 Impreza 2.5RS and I also have an ej20 shortblock. My Impreza has a 65 shot nitrous kit so I was wondering if I mess something up, would the SOHC heads fit on the ej20? also if it does fit how would the car run without a turbo? If the heads will fit, everything else should right? What head gasket? RS or WRX?
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Old 07-03-2004, 03:32 PM   #2
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Well, Ej20 heads wil fit on an EJ25 block, so probably yes, but you will need longer head bolts.
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Old 07-03-2004, 06:00 PM   #3
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Can you put a pair of DOHC heads on the factory 2.5SOHC motor?
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Old 07-03-2004, 06:12 PM   #4
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Fit ya, run like a pile of crap... unless you have a stand alone ecu and even the the CR is very low for a NA car. Something around 7-8 to 1 I dont remember exactly.
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Old 07-05-2004, 01:11 PM   #5
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why would u want to? Those are the crappiest heads for a subaru. Forget what everyone says, they lied. The valvetrain is weak, 6200 rpm, sohc. How can u think about puttin this on a wrx block ?*flame suit on*
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Old 07-05-2004, 03:13 PM   #6
jamesfacts
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Not to flame.... but why?
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Old 07-05-2004, 05:59 PM   #7
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because i already have the shortblock from a previous project and I just wanted to see if the heads on my car now would fit that shortblock. >Just trying to learn more, don't actually plan to do it.<
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Old 07-05-2004, 10:41 PM   #8
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Quote:
Originally posted by RyansJDMgc8
Can you put a pair of DOHC heads on the factory 2.5SOHC motor?
Yes you can. I just did this. The CR is not 7-8:1......maybe if you put the EJ25 heads on the 2.0 block......

I won't comment on the DOHC heads flow capabilities as I don't know the exact numbers, but I'm quite pleased with their performance. My set has been mildly ported and heavily polished. Whn the motor is running, I'll be able to report any gains over a stock 98RS motor.


Jay Storm
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Old 07-05-2004, 11:48 PM   #9
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Quote:
Originally posted by ImprezaRSfan!
why would u want to? Those are the crappiest heads for a subaru.
Um, you're joking, right?
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Old 07-06-2004, 12:40 AM   #10
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ya (as i look at ur sig lol). But why would u choose those over wrx or v.7/8 sti heads?
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Old 07-06-2004, 11:37 AM   #11
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Quote:
Originally posted by Storm
Yes you can. I just did this. The CR is not 7-8:1......maybe if you put the EJ25 heads on the 2.0 block......

I won't comment on the DOHC heads flow capabilities as I don't know the exact numbers, but I'm quite pleased with their performance. My set has been mildly ported and heavily polished. Whn the motor is running, I'll be able to report any gains over a stock 98RS motor.


Jay Storm
What is the CR?
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Old 07-06-2004, 09:49 PM   #12
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final compression ratio depends on head gasket used. since the SOHC heads have slightly more volume in the combustion chamber my guess would be the compression ratio is slightly less than the wrx ej20 if the stock ej20 headgasket was used.

Last edited by inpreza kid; 07-06-2004 at 11:46 PM.
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Old 07-06-2004, 11:23 PM   #13
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Yeah I asked about the head gasket thing in the very first thread.
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Old 07-07-2004, 08:26 AM   #14
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Quote:
Originally posted by inpreza kid
final compression ratio depends on head gasket used. since the SOHC heads have slightly more volume in the combustion chamber my guess would be the compression ratio is slightly less than the wrx ej20 if the stock ej20 headgasket was used.
Ya, thats what I figured... something like 7 or 8 to 1. An ej22 will for from ~7.4 to ~8.0 on RS heads depending on the gasket.

Storm said its not tho...
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Old 07-07-2004, 08:40 AM   #15
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I'll be doing the same set up soon. It will work. the CR will drop but not that much. You should use the wrx head gaskets. You WILL need to up grade the valve springs. Also use the rs timing belt.

Jason
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Old 07-07-2004, 09:25 AM   #16
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well...since we're talking about this...what about 2.2L NA SOHC heads from a 2.2NA legacy....on the 2.0L shortblock...I've got the shortblock, and a junkyard engine is not much money.

yeah...do the valve springs...

sjd
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Old 07-07-2004, 09:33 AM   #17
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Theres a difference betwen legacy heads and RS heads... the leagacy heads suck.
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Old 07-07-2004, 09:51 AM   #18
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LOL!!!

anyone throw a website together of heads on the flowbench? all the different ones?

sjd
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Old 07-07-2004, 11:17 AM   #19
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http://www.cobbtuning.com/tech/sohc/page2.html

Scroll to about the middle, they did some tests.

Oh yeah, and if the SOHC RS heads are soooo bad as some people here said, check out this thread : http://forums.nasioc.com/forums/show...hreadid=589189
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Old 07-07-2004, 11:41 AM   #20
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Quote:
Originally posted by totoherbs
Theres a difference betwen legacy heads and RS heads... the leagacy heads suck.


???? What's the differance? Fill me in.
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Old 07-07-2004, 11:49 AM   #21
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Toto is talking about the 2.2 turbo Legacy heads. You should check out that Cobb article I posted, VERY informative.
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Old 07-07-2004, 01:28 PM   #22
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I did read both of them. They were very good articles. 2.5 heads were the best #'s of all of them. And the guy with a sweet 1/4 mile. I saw that post a couple of days ago. That's what I'm talking about.

Jason
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Old 07-07-2004, 07:50 PM   #23
Hurley 2.5 WRS
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Wedge is right, just listen to the man!
RS heads flow very well.
but back to the original post...
going from a 2.5 to a 2.0 block would probably require stand alone managment.
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