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Old 05-29-2005, 09:27 AM   #1
tmeh
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Default ej20 DOHC heads onto 2.5 SOHC NA block

can anyone provide maybe a pic of the two, i'm thinking about the possibilities of putting DOHC WRX heads on a 2.5L NA to up the redline a bit and increase the overall flow... maybe i'm way out to lunch but i can't seem to find a similar undertaking anywhere.

the car would be run NA... i'm sure EMS would be required as well

i'm just really wondering if the bolts, coolant and oil passages would line up

if i had a spare 2.5 block i could try it, but right now it's required to move my car around... the wrx heads i've got. i'd like to use the ej20 intake manifold as well(TGVs are very deleted).

opinions and experiences appreciated!!
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Old 05-29-2005, 02:58 PM   #2
MeshmeZ
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from what i have heard the stock sohc heads flow well to begin with, and as it is, the power from the 2.5 na is dissapearing by the time you hit 6000rpm anyway. im not really sure upping the redline would make much difference. i would venture a guess that its not going to be worth it for the money you will spend to do it. thats just my opinion though.
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Old 05-29-2005, 08:31 PM   #3
Kostamojen
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Doesnt work that easily.

If you use WRX heads, you have to use the WRX intake manifold, and everything that goes with that (wiring, fuel lines, etc.)
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Old 05-29-2005, 10:56 PM   #4
tmeh
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i've got it all already

would the heads line up at all??

i'm not 100% serious about doing this it's mainly for interest, i wonder sometimes how Lego this car really is


i figured the wrx heads would flow better, thats an important bit of info completely defeating the purpose it all
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Old 05-30-2005, 03:04 AM   #5
Kostamojen
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The heads line up fine with the block, dont know about piston/valve clearance. The problem is that the bolt patterns for the intake manifolds are completely different and are not compatible. So you have to go with whatever intake manifold/etc. with the heads.

So basically, if you want to do WRX heads, you have to do almost full WRX swap to use them...
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Old 05-30-2005, 07:37 AM   #6
tmeh
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nice. thanks!

Last edited by tmeh; 05-30-2005 at 05:18 PM.
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Old 05-30-2005, 11:11 AM   #7
Matt Monson
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What are people talking about here? The phase II SOHC EJ25 heads use the exact same manifold bolt pattern as the USDM WRX's. Everything from '99 on is the same. If they are '98 or earlier WRX heads, then they use the same pattern as our '98 EJ25 DOHC heads. Coolant passages and head bolts, etc are totally a non-issue.

Regardless, this swap is a crap shoot. The smaller combustion chamber of the EJ205 heads (45cc vs 49cc of the SOHC EJ25) will bump your CR up to around 11:1, so gains will be had there. But the EJ205 heads flow 220cfm and the EJ25 SOHC heads flow 240cfm, and have substantially larger ports. Only if you replace the turbo camshafts with a pretty aggressive cam will you be able to make use of that extra CR.

Xephyr has a wagon with a similar setup, but he used the USDM DOHC EJ25 heads (which flow better than either of the above heads) on a phase II Ej25 block. He uses a 272 degree HKS cam meant for the WRX, and is getting about 5whp less than I am with my set up. But our powerbands are night and day different. He's got nothing below 4500rpm, and then it is like Vtec. It cranks all the way to 7000rpm.

My car comes on nearly 1000 rpms lower, and peaks at 5900rpm. But my torque curve is ridiculous. Over 200ft/lbs of torque from 3000-6400rpm when fuel cut hits. My power under the curve is substantially more than his...
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Old 05-30-2005, 05:18 PM   #8
tmeh
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wow

thanks for the info

idea abandoned
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