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Old 02-20-2018, 12:05 PM   #1
Scooby Specialist
Member#: 170439
Join Date: Jan 2008
Location: Sioux Falls, SD
I <3 Lamp

Default 99 Outback engine rebuild... boost?

I've got a 99 Outback with the ej25D phase 2 bottom end and phase 1 heads.

Bought the car recently and have pulled the engine with my wife to put all new gaskets in and re seal it back up. The stock pistons look fine and the bores have great crosshatching which is surprising considering it has 230k miles on it. Inside of the engine looks immaculate aside from carbon deposits. I have a gt2554 turbo sitting in my garage begging to be put into something. I know the stock compression ratio on this engine is something like 9.7:1 but if I put ej255 pistons in, it should drop to about 8.5:1. My thought is to possibly drop some stock ej255 pistons in that were pulled from a low mileage car getting forged pistons, then run stock ecu with the gt2554, wrx top mount, and a sti fuel pump for awhile. I'm planing on making my own uppipe and downpipe since I have a welder and fabrication experience. Then when I finish figuring out all the wiring I would drop in a microsquirt based diypnp ecu with some sti 565cc injectors.

Not looking for gobs of power obviously, but I do want some semblance of reliability for relatively cheap. Keep in mind I already have the injectors, ecu, and wrx top mount intercooler. I've yet to buy pistons for obvious reasons, same with the sti fuel pump.

My question is, would ej255 or ej257 stock pistons and stock ecu combo be reliable enough for a couple months without issue if I ran 91?

I Have...

  • 99 outback with EJ25D, taken apart in garage
  • GT2554 Turbo from a saab 900 (7psi wastegate)
  • 565cc STI side feeds
  • 02 WRX top mount intercooler
  • DIYPNP Megasquirt ecu

I may need...

  • ej255 or ej257 pistons and rings, used probably.
  • wrx or sti fuel pump

Should I slap the turbo pistons in and run the stock ecu til I put the megasquirt in with the 565cc injectors?
Overall this only should cost me an additional $200 or so since I should be able to scrounge up enough steel pipe for the uppipe and downpipe.
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Old 03-30-2018, 02:31 PM   #2
Scooby Newbie
Member#: 437670
Join Date: Jan 2016
2005 2.5 SC OB


Sorry nobody replied earlier.

You should not run any boost with stock ECU. You can run the turbo pistons with stock ecu, you will just be down on power, but if you run boost with no engine management, you can destroy the motor obviously.

You might need to check to see if you need to run turbo rods also. I'm not sure if your 99 Rods are EJ255/257 length.

Last edited by pcampbell; 03-30-2018 at 02:51 PM.
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Old 04-03-2018, 09:15 PM   #3
91 RS RA
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Member#: 457410
Join Date: Oct 2016
Chapter/Region: International
Location: Christchurch, New Zealand
1991 Legacy RS RA


Also the EJ25D is not great with head gaskets, yes this can be improved with new and better head gaskets, but I wouldn't trust it with much boost.
And not have a correct ECU will make everything much worse as well.
What are you going to be using for boost control and what sort of max PSI are you thinking?
If you do want to do it, leave it at wastegate pressure, enjoy it till something goes on it and in the mean time save up for a nice turbo short block and then rebuild with better bottom end
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