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Old 08-04-2008, 12:58 AM   #1
HillbillyLes
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Join Date: Apr 2008
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Location: Central Missouri
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2002 WRX Speedwagon
Platinum Silver Metallic

Default RS DOHC to SOHC swap...

Well, it appeared that it would be as close a plug-n-play swap as possible to get a reliable engine in the 98 RS opposed to more cash and considerable downtime for one of the more common turbo engine swaps.......It appeared!!!

first I found the engine. then I realized it was a Drive by Wire TB'ed engine so I started the search for an older drive by cable intake. Now I've invested a considerable amount of time and effort and money into finding an intake and buying it, now I have been informed that the electronics between the DOHC and SOHC are entirely different and cannot be swapped....it has been suggested that the only option I have to get this to work is to disassemble my commuter car's DOHC engine and put the DOHC heads and intake on the SOHC shortblock....

I have a couple of people i was referred to who are either gurus or are familiar with what I thought would be fairly simple.

does anyone else have any info that might help me to avoid doing engine teardowns...I really don't have the space or the resources (and can't afford the downtime on my only work transportation) to do the head and intake swap if I son't have to...besides, the SOHC is a 30K mile car and if I am going to tear it down and swap parts, I probably should have the heads gone thru since they are over the 100K mile mark (this was a salvage engine replacing the original engine 6 years ago until a few weeks after I bought the car this spring and it developed a rattle in the bottom end). That means more money and downtime and I won't even realize a performance increase to offset the considerable amount time money and effort invested


Come on... can't someone shed some light and hopefully offer me a glimmer of good news??

Les
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Old 08-04-2008, 03:16 AM   #2
HillbillyLes
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Platinum Silver Metallic

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I did a search and read several similar posts back to 2006 or before...saw a lot of opinion and conjecture and even an argument or two but nowhere did I see where anyone had returned after the project to answer how difficult it was.

The only things that kept coming up were that the harness plugs/wiring were different between the DOHC and SOHC meaning splicing...actually the pins are removable from the harness plug and if you trace the pin's wire back to it's respective sensor you can then move that pin to the correct place on an empty DOHC harness...pain? I suppose, but in my case it will allow me to continue driving my RS to work and back until the SOHC is ready to drop in and will cost me very little other than time which it is going to cost, anyway.

I suppose since I have a background in electronics I will start on the harness tomorrow...or the next time I get a chance. Now I need to find a empty harness plug off of a 98 DOHC to put the corrected pins in out of the 2000 SOHC intake's harness plug...

Les
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Old 08-04-2008, 07:48 AM   #3
Storm
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If you start with the original engine harness, you'll eliminate most of the wiring issues, as the main plugs will all play nice. It gets tricky when the cam sensor on the SOHC is further away from the crank than the DOHC, so that plug may need extended. The shapes of the coil, TPS and IAC sensors may be different as well....so those will need spliced. Work through those few items and you should be up and running in short order. Doing everything to make sure you don't throw a CEL will likely require some light fabbing of block off plates or brackets.

Check the water temp sensors on both crossover pipes before you start dropping stuff in the car. It might be easier to swap them to keep from splicing the wiring.

Good luck,
Jay
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Old 08-04-2008, 10:50 AM   #4
HillbillyLes
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Good Advice...Thanks for the heads up. I will keep that in mind.

MUCH APPRECIATED!

Les
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Old 08-04-2008, 10:52 AM   #5
HillbillyLes
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2002 WRX Speedwagon
Platinum Silver Metallic

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Wonder if anybody has a spare DOHC engine harness out there they would be interested in getting rid of...since mine is being used on the RS. that way I can work on the harness in the garage while I drive the car.

Les
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Old 08-04-2008, 11:54 AM   #6
greenspeed
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Les...I got a DOHC harness off my 98 leg.

I did a SOHC short block with my DOHC heads on my leg. I never compression tested the engine to see what exactly would be my compression, but tearing then engine down, putting in new hg's isn't a bad idea. It's actually really easy on a subie. I would suggest going that way...or KEEP modding your own way and keep the community in step...

If my harness can be used for experimental services I'd be happy to work something out with you...as you've been in contact with me frequently about parts...
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Old 08-04-2008, 11:57 AM   #7
greenspeed
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shart pay shipping and the harness is yours...shoot me a pm les...im excited to see you get this working...
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