engine swap in to a 99 obs
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This is a discussion on engine swap in to a 99 obs within the Builds forums, part of the Tech & Modifying & General Repairs category; ive done alot of searching and got a pretty good idea about swapping either an sti or wrx engine in ...

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    engine swap in to a 99 obs

    ive done alot of searching and got a pretty good idea about swapping either an sti or wrx engine in to the car. i am also swapping a manual trans in to the car at the same time. i only have a few questions that i really couldnt find any definitive answers on.

    1. wiring - wiring is not a huge problem for me, certified in automotive electrical wiring and diagnosis and through frieghtliner but more towards the multiplexing side of things. anywho..... i have done tons of swaps srt in to older neons, hondas like there going out of style, northstar in to a jetta....and so on, but as of the subbie i get conflicted answers about harnesses. do i need a donor car for the harness? or can i splice in to the factory obs harness and repin the ecu connectors. i also can not seem to get a straight answer if i dont need a donor car for the harness...which harness do i use. motor obviously, but what else....

    2. difference in the turbocharged ej20 and ej25... sound, performance, able to withstand abuse at times (voluntary fire fighter), aftermarket support between the two (im guessing they would be almost identical.)

    3. drivetrain - im planning on swapping over to a manual trans. would like an sti drivetrain, but its not a MUST HAVE. i would be happy with just the wrx or with what i have now (minus the auto trans). once i do swap over though, i would have to switch the rear diff gearing out to match the front diff correct?

    4. running cat less.. how to bypass the downstream o2 sensor without throwing codes, and without getting into the ecu. ive heard of the spark plug nofouler trick, but is this really effective?

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    Registered User SKI.WRX's Avatar
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    1. I do not know for certain but I don't think the ECU from the OBS will have the proper tables to run the turbo and associated parts. If you go to STI motor you will need to either get an sti harness or get some non AVCS heads and get the combustion chambers match since the ECU will definitely not be able to run AVCS.

    2. EJ257/255 has more low end grunt and will potentially make more power. sound is pretty similar between my EJ205 and my friends EJ257 hybrid build. both will last if taken care of.

    3. you will need an after market DCCD controller for the STI drive train but a WRX drivetrain would bolt right up.

    4. anti foulers have worked for a lot of people. electronic fix in the ECU is the best way to go though since you will need a tune anyway to run catless.

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    1. You're going to want to use the ECU that goes with the engine you are using, so I would get the engine harness as well as the body harness that matches the ECU/engine. There will still be some splicing I'm sure, but this will make your life a lot easier. You don't need a donor car, just the wiring harness.

    2. Given the same exhaust configuration, the two engines sound relatively the same. The 2.5L will make considerably more torque down low, and more power over all. That's something to consider when driving around town. And for what it's worth, I actually got better fuel economy after switching to the 2.5L because I didn't have to press the gas as much. As far as abuse and aftermarket support, they're virtually the same.

    3. You will probably want to swap the diff.. although I'm not sure about the existing diff in the obs, as well as the axles, that is an unknown to me. I do know if you want to put an 05+ STi transmission into a WRX you need to swap everything over, driveshaft, diff, axles, hubs, etc.

    4. I would just tune it. The stock tune sucks, and if you're only interested in turning off the CEL, it's as simple as clicking a check box next to rear O2 sensor in RomRaider.

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    Brydon teaches you to merge a harness - Subaru Impreza GC8 & RS Forum & Community: RS25.com

    You need the dash harness for the car you're swapping into and the entire harness out of the car you're swapping from.
    Last edited by Drews; 05-01-2013 at 02:08 PM.

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    Quote Originally Posted by Drews View Post
    Brydon teaches you to merge a harness - Subaru Impreza GC8 & RS Forum & Community: RS25.com

    You need the dash harness for the car you're swapping into and the entire harness out of the car you're swapping from.
    this is what im talking about....why would i need the entire harness?

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    Quote Originally Posted by boosted to 26ps View Post
    this is what im talking about....why would i need the entire harness?
    To make sure you have everything you need. For example, fuel pump relay is quite important. Your other option is to just do a dash swap from whatever car you're using as a donor. But then you have to drill holes and cut the firewall to fit the AC and heater core and blower. This swap has been done a ton.

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    Quote Originally Posted by Drews View Post
    To make sure you have everything you need. For example, fuel pump relay is quite important. Your other option is to just do a dash swap from whatever car you're using as a donor. But then you have to drill holes and cut the firewall to fit the AC and heater core and blower. This swap has been done a ton.
    so if you use the harness you can use your factory dash?

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    Quote Originally Posted by boosted to 26ps View Post
    so if you use the harness you can use your factory dash?
    I'm not sure I follow your question. Maybe my previous post wasn't clear. There are 2 ways to do the swap. If you want to keep the factory dash in your OBS then you need to do a harness merge. Or you can use the dash out of the WRX or STI that you're pulling parts out of and use that dash.

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    Quote Originally Posted by Drews View Post
    I'm not sure I follow your question. Maybe my previous post wasn't clear. There are 2 ways to do the swap. If you want to keep the factory dash in your OBS then you need to do a harness merge. Or you can use the dash out of the WRX or STI that you're pulling parts out of and use that dash.
    i noticed i worded that kinda f'ed up. but you still got what i was saying. ok so next question is ive been looking around on the net trying to find a place that sells swaps and cant really find any place that has the engine i want. what would you recommend for sites to check out in the area of swapping?

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    Quote Originally Posted by boosted to 26ps View Post
    what would you recommend for sites to check out in the area of swapping?


    nasioc classifieds.. or me, I have a complete 2002 WRX swap for sale (but the engine needs a new cam gear, timing belt, leak down test.. and I still need to pull the body harness).

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    Quote Originally Posted by boosted to 26ps View Post
    i noticed i worded that kinda f'ed up. but you still got what i was saying. ok so next question is ive been looking around on the net trying to find a place that sells swaps and cant really find any place that has the engine i want. what would you recommend for sites to check out in the area of swapping?
    Do you just want the harnesses done? IWire on RS25 is a popular choice for the guys that need harness merges. That link I posted earlier in the thread is a GREAT resource if you want to attempt the merge yourself.

    Quote Originally Posted by MainFrame View Post
    nasioc classifieds.. or me, I have a complete 2002 WRX swap for sale (but the engine needs a new cam gear, timing belt, leak down test.. and I still need to pull the body harness).
    I need those harnesses

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    thanks...i looked at that link and man...thats a good right up. as of buyin the conversion, im looking down the road like this coming tax season. i got 2 kids now and one more on the way. so got to save my pennies til after he/she is born

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