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Old 08-26-2012, 02:43 PM   #1
xhector2013x
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Impreza GC8 n/a 2.5 head help

So im gunna be buying an 01 rs today or tomorrow, the guy bought it as a project and turns out the SOHC he swaped has some noise in the bottom end, but hes including a 2.5 DOHC for me to swap he is including a DOHC ecu with the car but no harness. so the question is can i just swap the SOHC heads onto the DOHC block and run the same SOHC ecu and wiring harness?
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Old 08-26-2012, 03:02 PM   #2
EmanLives
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it's not that simple, they're completely different engines.
sorry that just the short answer.
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Old 08-26-2012, 04:50 PM   #3
GrundleJuice
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I think this has been done before. have you searched the forum?
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Old 08-27-2012, 09:23 PM   #4
geronimo81
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Quote:
Originally Posted by xhector2013x View Post
So im gunna be buying an 01 rs today or tomorrow, the guy bought it as a project and turns out the SOHC he swaped has some noise in the bottom end, but hes including a 2.5 DOHC for me to swap he is including a DOHC ecu with the car but no harness. so the question is can i just swap the SOHC heads onto the DOHC block and run the same SOHC ecu and wiring harness?
It is that simple. Your compression ratio will be slightly lower but not significantly. I know a shop that buys dohc turbo motors from Europe and swaps the shortblocks into all types of NA 25's and they run great.

The next question is what kind of condition is the dohc ej25 in?
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Old 08-28-2012, 10:09 PM   #5
DerekNichols
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yes you can swap 2.5 sohc heads on a 2.5dohc block. make sure you use the Dual headgasket, as there thicker. The dohc pistons come past the deck a bit and need the extra clearence inthe gasket. Thats the main thing! your intake from your sohc 2.5 will fit on the dual block with sohc heads.

Only other thing is there is a lil bracket above the water pump that differs from dohc to
sohc. Other than that, Its a very simple swap.

Pull the heads off that Dohc and when you have just the block, check for knocks the best you can. Listen+ Feel, every piston at/and before tdc. and also at/and before Bdc

Last edited by DerekNichols; 08-28-2012 at 10:16 PM.
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Old 08-30-2012, 04:18 PM   #6
Matt Monson
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Contrary to popular belief, there were in fact phase II DOHC Ej25s made. When you get the heads off, post a picture of the tops of the pistons. Then we'll tell you which head gaskets to use on reassembly.
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Old 08-31-2012, 06:15 PM   #7
xhector2013x
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Quote:
Originally Posted by geronimo81 View Post
It is that simple. Your compression ratio will be slightly lower but not significantly. I know a shop that buys dohc turbo motors from Europe and swaps the shortblocks into all types of NA 25's and they run great.

The next question is what kind of condition is the dohc ej25 in?
its in pretty good condition from what i can see
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Old 08-31-2012, 06:19 PM   #8
xhector2013x
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ill post a picture of both motors
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Old 08-31-2012, 06:43 PM   #9
xhector2013x
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im clueless as to how to upload pics on here so here i made a photobucket and i have the images there. i think you can find out which is which
http://s1251.photobucket.com/albums/hh553/xhector2013x/
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Old 08-31-2012, 06:46 PM   #10
xhector2013x
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Quote:
Originally Posted by Matt Monson View Post
Contrary to popular belief, there were in fact phase II DOHC Ej25s made. When you get the heads off, post a picture of the tops of the pistons. Then we'll tell you which head gaskets to use on reassembly.
ill pull the heads tomorow and post the picture, i worked on that car enough for today
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Old 09-01-2012, 09:35 AM   #11
RaceTSI
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I have an 02 2.5 forester engine in my 97. the 2.2 in it crank walked leaving the bottom end useless. I swapped over my heads to the 2.5 motor and used the 2.5 motor head gaskets being the bore for the 2.2 is slightly smaller.

I used the stock SOHC harness, manifold, exhaust (same heads it came with), etc. The only thing I changed was the bottom end, and the head gaskets. Everything else can be swapped over. I do run premium now as it is higher compression. supposedly like 10.9:1? Its faster than a friends RS and my car is slightly heavier.

main thing is make sure the head gaskets are the same bore.
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Old 09-01-2012, 01:19 PM   #12
xhector2013x
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yeah i was imagining that thats what i was going to have to do, so would this be the same procedure for a 2.5 head?
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Old 09-01-2012, 10:36 PM   #13
xhector2013x
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Old 09-03-2012, 01:36 PM   #14
xhector2013x
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yup everything bolted up and iv got compression , iv got a picture in my photobucket
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