STI block SOHC heads completed.
Thread Starter
Registered User
Joined: Jan 2003
Posts: 144
From: Colorado
Car Info: 2000 2.5 RS USDM STI block, SOHC heads GT25 Ball bearing turbo, TMIC, TXS BOV, Tial wastgate, etc...
the sti rods are a little different, in fact on the sti they are shorter than the N/A rods. I will see if I can attach a picture later on, but I am 99% sure that the sti rods are shorter
Thread Starter
Registered User
Joined: Jan 2003
Posts: 144
From: Colorado
Car Info: 2000 2.5 RS USDM STI block, SOHC heads GT25 Ball bearing turbo, TMIC, TXS BOV, Tial wastgate, etc...
well sorry about the useless info.. 
any way yues they are the same so your crank will fit.
any way yues they are the same so your crank will fit.
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STi Heads
I see a lot of guys replacing short blocks to STi and keeping the original heads. Has anyone tried putting STi heads on a 2.5RS. I would think the heads would make a big difference. I'm thinking about it but I haven't heard of anyone doing it.
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sti heads use a different intake manifold which makes for a nightmare on a 2.5RS
plus the 2.5 ECU (99+) would never work with the DOHC setup
(cam sensors..)
also the 2.5RS SOHC heads are awesome heads..
the roller / rocker setup is considered by many to be supior to the more friction inducing dohc setup.
you do suffer the drawback of cam tunability.. anything else besides that can be replaced with components supior to sti for not too much cash.
plus the 2.5 ECU (99+) would never work with the DOHC setup
(cam sensors..)
also the 2.5RS SOHC heads are awesome heads..
the roller / rocker setup is considered by many to be supior to the more friction inducing dohc setup.
you do suffer the drawback of cam tunability.. anything else besides that can be replaced with components supior to sti for not too much cash.
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Posts: 18,369
From: Reno, NV
Car Info: 1993/2000/2001 GF4 mostly red
I'm working on the intake manifold/head choice issue right this second. I will be posting up all the workable combinations I find, and of course at least ONE will actually work. 
Big Baller
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Joined: Nov 2002
Posts: 1,821
From: Washington
Car Info: 93 BG5, 00&01 GM6, 06LGT, 07STi
the beauty of this swap is that we don't need to change engine managment. Also, we get lower compression (9:1-ish) but not turbo engine low (8:1 ish). This helps us retain all that torque we're used to but also push more PSI. Also the STi block is obviously stronger so we up our max power capability (400+ HP).
However if we put STi heads on a normal 2.5RS block then we're totally screwing ourselves. We then have to change our entire engine management system. PLUS, we still have a weak bottom end that's only capable of about 350HP before crapping itself.
We haven't removed any of our weak links and we've created a huge PITA.
If someone wanted to do heads, they should do a total conversion. Not just that, but the cost of a conversion could buy us a stronger block and some stronger gears. An STi block runs around 1400 bucks. Heads are upwards of 2000 then add on wiring harness, ECU, Intake manifold, accessory components (because they're not the same mounting wise) etc etc
However if we put STi heads on a normal 2.5RS block then we're totally screwing ourselves. We then have to change our entire engine management system. PLUS, we still have a weak bottom end that's only capable of about 350HP before crapping itself.
We haven't removed any of our weak links and we've created a huge PITA.
If someone wanted to do heads, they should do a total conversion. Not just that, but the cost of a conversion could buy us a stronger block and some stronger gears. An STi block runs around 1400 bucks. Heads are upwards of 2000 then add on wiring harness, ECU, Intake manifold, accessory components (because they're not the same mounting wise) etc etc
Registered User
Joined: Nov 2002
Posts: 99
From: Delta, BC, Canada
Car Info: 2000 Impreza 2.5RS BRP
That's what I had in mind when I go turbo - EJ257 short block with SOHC heads, just so that I can keep my wiring job simplier. The main argument against bolt-on in the 2.5RS is the block, and once swapped, makes a sweet setup. You can't rev as high as the EJ20s, but guess what - the install would be easier than doing a JDM/USDM swap because you don't really need to muck around the harness, keep the displacement as well
Man, if only I had the money and the right shop locally to do this...
Man, if only I had the money and the right shop locally to do this...