Engine difference - WRX vs Legacy GT

[BrandonDrums]

First, I know the donor vehicle is a 2002-2007 Impreza. I've been wondering that if I picked up a really cheap non-turbo Impreza with a bad engine as a donor, would it be possible to use a good engine from an '06 - '07 Legacy GT? Is there a difference between an '06 - '07 WRX and an '06 - '07 Legacy GT? Do we have any Subaru experts here?

I bought a Legacy GT new in '07. The engine and trans were great! Got rid of the car after 2 years because the front seats were TERRIBLE! My wife got a back ache within 30 minutes after we bought it. It took about a month for me to get one, but I did. I ended up having to replace the head rests (tilted too far forward) and disconnect the lumbar support mechanism. Those seats either had too much lumbar support or way too much lumbar support.

I have an '00 Legacy Outback wagon - I feel the same way about the seats. However, I found that because the electonic seat adjustment is only for the seat bottom-not the back, when I have the seat as low as I want it the lumbar hump is too high and my back hurts. I have to sit much higher than I want to the lumbar support is actually at my lower back. Perhaps you had the same issue.

As far as swapping engines into a 02-07 wrx, the engine I have in my 2005 wrx now is actually an EJ255 from an 05 legacy GT but with forged, STI spec compression (lower compression) pistons so you can call it an EJ25X because the only component that was different from an STI engine (the pistons) were replaced.

For an 02-05 wrx donor/ecu running either a EJ255 or an EJ257, you'll just need a cam sensor adapter. There are many vendors and 2-3 manufacturers for these. Mine is a Cosworth.

Cosworth at Rallysport Direct
Torque Solutions adaptor at Vivid Racing

I'm not sure if the Drive By Wire system is the same in the 06-07 wrx and the Legacy GT. The Legacy GT also has AVCS which the 02-05 wrx does not have. If you can run the ECU from the Legacy GT, you'll need to run the legacy's intake manifold which has the drive by wire throttle. If you don't have that ECU, then you'll need to run the WRX's intake and throttle. Again, 02-05 wrx has a cable throttle, the 06+WRX has a drive by wire setup and AVCS.

If your donor WRX is 02-05 AND you have to use the 02-05 ECU without AVCS, it is recommended but not required that you plug the AVCS cam's oil passages and run non-avcs cam pulleys. There are a few opinions on this but my personal thought is that the AVCS cams which work by oil pressure being sent through a oil passage in the front of the camshaft into the cam pulley itself have a bit of "float" or play when the avcs control solenoids are unplugged as they are when you swap to a non avcs wrx.

I haven't found much proof of this but on my build which had the unplugged AVCS cams still on the engine, I felt some lack of low-end torque that wasn't present on my 2.0L. Below 2500 rpm, the engine would bog when I used more than ~15% throttle. That wasn't an issue on my 2.0L and regardless of AVCS, a larger engine should have at least a little more torque down low.

Here's probably the best write up on how to plug the AVCS passages. It's easier than you think.

http://forums.nasioc.com/forums/show....php?t=1356918

The last tidbit of mine is the Legacy GT most likely is an automatic and there can be some issues running an ECU for an auto when you swap a manual transmission in it. You may be able to flash a manual transmission Map/Rom to the auto's ECU unit and go OR tune around it. However, I don't know enough about the specific ECU's to confirm cross compatibility and with what.

You can probably find some of that information over at openecu.org along with the tuning sections on NASIOC.