IA Performance

I'm not sure if this is the right forum, they are both 2.5L subaru turbo motors so I figured this location is the best bet. Please keep in mind, this is just our findings.

This is the closest 'Apples to apples' to date:

Donor motor:


I, like many people on here, wondered what the true power difference was of the ej255 vs ej257. We have been selling ej255 long blocks for quite some time and every so often we'd get a customer that was hell bent that the ej257 was that much better (cams mainly). I couldn't give an honest answer without testing it first hand. Here is how it happened:

2007 US Sti EJ257 w/ stage 2 COBB & n2o dyno tuned with Ecutek (this was one of the first 07's in the entire US, at the time only EcuTek offered tuning support). Regardless, the EcuTek software did a fine job of controlling the car. The short of it is that the motor had a nitrous back fire after the customer did some 'spirited driving'. We needed something to replace it with. I made a few calls and had a EJ255 w/ EGR heads here at the shop in a matter of days. Every single usable stock part was reused on this build, exhaust manifold, intake manifold, turbo, etc. All items were in great condition that were reused. Intercooler, throttle body, and some gaskets were replaced with new stock pieces. This car was setup identical to how it was the first time we had it. Nitrous was removed from the car(don't give any input on nitrous, I don't care to hear a speach, customer wanted n2o so they got it).

Test results info:
- all runs were done on 91 octane
- Temps were hotter with the EJ255, 88 vs 74F
- EJ255 long block with ej255 EGR heads (found on 06+ models)
- More HP
- Less TQ, but less boost. If we ran higher boost the torque would have been the same if not more. (it wasn't worth it to us to push the car for the extra dyno numbers)

End Result:
- EJ255 >= EJ257 at stage 2 power (and anywhere lower)
- slightly higher compression meant lower boost would net higher power gains (8.4 vs 8.2:1 in ej257)
- we have not tested a car like this on a 400 whtq level, but I do not imagine power results would change much. I do not foresee these motors to be within 5% of each other for power.
- We feel that similar head types (non EGR vs non EGR and EGR vs EGR will net similar power results). If you tested EGR vs a nonEGR car then the power may be higher.

Edit:
Head definitions
- EGR heads (as I call them) are the new age emission compliant Exhaust Gas Recirc design where an air pump adds outside air to the exhaust mixture to allow for cleaner emission results

DYNO sheet info
- Solid run is with EJ257 done in November
- Dotted run is with EJ255 done in August

Tuning
- I did not do the initial tune, it was done by another. The ej255 touch up tune was done by me. Only items changed were lowered boost pressure and added fuel from 3800 RPMs upwards under WOT. Timing, AVCS, etc all stayed the same. The reason we lowered the boost was that our customer runs Mexico unknown fuel. Sometimes it is 91 sometimes it is 87 We've learned to be more conservative for our Mexico client cars due to this. I.E. with higher boost we could run the same torque as the ej257, if not more.



Feel free to post any questions or concerns. We sell used EJ255 motors, price varies, but they are usually around $3500 and in stock every day.

Stephen