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Old 11-16-2019, 09:14 PM   #1
Colonel Ives
Scooby Newbie
Member#: 211558
Join Date: May 2009
Location: Seattle
2002 WRX sedan

Default EJ25X with AVCS into '02 WRX using JDM V7/8/9 ECU?

I'm attempting to do all of my research leading up to a 2.5 L swap into my '02 WRX.

The typical options of course are:

1. Hybrid
2. Transplant entire EJ25X long block and don't use AVCS
3. #2 plus transplanting the STi ECU, every wiring harness, steering column, the kitchen sink, to get AVCS

#3 sounds like a nightmare. It would probably make more sense to just buy a used STi and build its motor. Which I'm not excited about. Options #1 and #2 are very sub-optimal. If I'm going to go through all this trouble I think I really want to have AVCS.

I found that at least one vendor sells add-on wiring so that people swapping in a JDM EJ207 and a JDM ECU don't have to replace their USDM harness. The only real reason to swap the ECU is for AVCS support. But, people doing that swap aren't also swapping steering columns, every harness in the vehicle, etc. All they have to do is swap the ECU and upgrade the harness, apparently. So, the JDM v7/8/9 ECU supports AVCS, and apparently can be swapped into a USDM WRX without having to mess around with also swapping in over half of the rest of the donor car's electrical system.

My question is: Why wouldn't it work to swap in a long block EJ257 along with a JDM STi ECU and a harness upgrade in order to have a fully functional EJ257 in a bugeye with AVCS ? The JDM ECU supports AVCS and also doesn't apparently require you to replace every damn wire in the vehicle in order for it to function. I haven't found a single post describing a successful build using this approach, which leads me to believe it won't work, but why?
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Old 11-16-2019, 11:37 PM   #2
Scooby Specialist
Member#: 395793
Join Date: Jul 2014
Chapter/Region: Tri-State
2005 92x Aero

Default EJ25X with AVCS into '02 WRX using JDM V7/8/9 ECU?

USDM avcs cams advance by up to 30* where JDM avcs cams advance up to 40*. The other aspect is DBW vs DBC (there's more than this but keeping it simple). To my knowledge all DBW ECUs are 32bit and there are a s**t load of body control electronics that are an issue swapping into a 16bit car. The easiest, most cost efficient and best engine option you can do is a DBC 207 if you want an STi engine. I personally don't see any advantage to using a 257 instead of a 207 unless you're not going to use avcs, which you seem to want. So get a 207 and save yourself the headache.

Last edited by snow_bound26; 11-17-2019 at 12:29 AM.
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