View Full Version : All EJ255 Engines are NOT created Equal

10-09-2010, 10:02 AM
Just wanted to post up some research I have been doing on the Engines in our Subies. The reason I want to post this is because some people want to swap an EJ257 into a legacy and that may not be necessary because some years they are the same. I had put some of this information in my members picture thread but thought it would be easier to find here.
To complete my "Outback XTi" project looks like Ill need the 6 speed, DCCD, yaw sensors, axels, and rear diff since in my year the engine is pretty much the same.

If you want to swap to the STI turbo and intake then that is a different story. I chose to just go aftermarket on the turbo.

What most do not understand is that there are more than one short/long block combinations that are labeled EJ255 but not all of them are built with the same parts. For example the EJ255 in the legacy GT/OBXT vs the WRX may or may not be the same.

Also there are a couple of years of EJ255 engines that are the same as the EJ257 in the STI of certain years with the exception of the turbo and intake.

So when looking at the data on the EJ255 make sure you are looking at what vehicle it came out of. If it was a WRX it may not be the same as the Legacy GT/OBXT.

This is also really important for the amount of boost you are running because the 05-06 legacyGT/OBXT/04-05 FXT and the STI have LOWER compression ratios to be able to handle more boost.

Here is a quick quote from some threads I dug up that sorta sums it up:

"The '05-'06 LGT/Outback XT uses the same longblock as the STi 04-'06. The longblock on the '07+ LGT/OBXT are the same as the '06+ WRX, which uses a 50cc combustion chamber instead of the B25 heads which it had started off with; 58cc.

There is NOTHING fancy about the EJ257. The '07 EJ257 is a nice upgrade because of the revised heads. The '08 EJ257 are nice for their DUAL AVCS."

Here is another:

"The '05-'06 Legacy short block was identical to the '04-'07 STI short block. The '08+ STI short block is different from the '07+ Legacy short block, although I don't have the specifics in front of me.

The only difference in the 05/06 LGT/OXT vs the STI of these years is the intake (black plastic instead of red alum and the turbo vf40 vs vf39) If you look at the part numbers even the heads, cams, valve springs, valves are the same.

Here is a link to a post by Jeff Sponaugle from Surgline Tuning with some part number picture charts:

http://forums.nasioc.com/forums/showpos ... stcount=16 (http://forums.nasioc.com/forums/showpost.php?p=23670210&postcount=16)

And the full threads:
http://forums.nasioc.com/forums/showthr ... ight=EJ255 see posts 27-28 and on

http://forums.nasioc.com/forums/showthr ... ight=EJ255 see post 29

Here is a good quote from Jeff in another thread that also sums this up:

""It is important to correct one thing:

It is not proper to catagorize these pistons as EJ255 pistons. There are two variants of the EJ255 shortblock. The first EJ255 shortblock used in the 05/06 Legacy GT, 04/05 *CORRECTED* Forester, and the Turbo Baja is identical to the EJ257 shortblock.

Thus you want to avoid grouping all EJ255 motors together, as the statements saying such would be incorrect. The correct way would be to either indicate the SB number 10103xxyyy.


And some more.....
As most of you know, the term EJ255 and EJ257 come from the first part of the ‘Engine Code’ assigned by Subaru. Unfortunately Subaru used the EJ255 code for two different configurations that overlapped in production. This use was in part driven by the assembly of the Legacy in the US plant ( SIA ) while the Impreza line was built in Japan. In the end, there are two different EJ255 motors. For clarity sake, I will call them version 1 and version 2. Note that this use of the term version is my own, not something that Subaru has used.

EJ255 Version 1:
Used in the 2005 and 2006 Legacy, as well as the 2004 and 2005 Forester. This engine uses the AB440 shortblock, which is the same shortblock as the 2004-2006 STI EJ257. The heads on these EJ255 are the AB650s, while the US 04-06 STI is the familiar AB640/910. The cams are the same between the EJ255 Version 1 and the EJ257.

EJ255 Version 2:
Used in the 2006-2008 WRX, the 2007+ Legacy, and the 2006+ Forester. This is the newer AIS equipped EJ255, which uses a slightly different AB630 shortblock, as well as the AB820 heads. The only difference in the shortblock of this EJ255 and the 04-06 EJ257 is the pistons. They are of nearly the same construction, but have a slightly larger dish volume. As for the heads, the AB630 heads have a smaller combustion chamber, but I do not yet know the exact specs. I suspect it is around 50ccs based on the engine config spreadsheet listed below. Subaru lists the CR at 8.4:1 vs 8.2:1 for the 04-06 STI engine.




Unclemat Quote:

"Engine wise 05-06 LGT and 04-06 STI are identical except intercooler and turbo. Yes, same long block. It has been proven by parts cross referencing long time ago.

07-09 LGT shares engine with 06-09 WRX.

07 STI is bit of an oddball, different block and heads. 08 STI has exclusive newer dual AVCS heads.

Of course otherwise the car is different. 08 STI is based of 05 Legacy platform wise, but the rear suspension is newer better design. 05+ LGT chassis however is a far better design than pre-08 Impreza.

Transmission 5mt vs. 6mt is obvious differene. 07-09 LGT SpecB have 6 speed transmission which is similar to 07+ STI transmission. Differences are: no front LSD, no DCCD, 5-6th gears are taller.

05+ STI has 5x114.5 hubs, Legacy has 5x100. Of course STI has far better brakes.

All mods that can be done to STI, can be done to LGT. SpecB is better start platform due to 6-spd and R180 diff."

AWD Bishop
10-09-2010, 10:19 AM
Great info. Thanks for sharing...

10-09-2010, 08:54 PM
Subaru has been known to "mix up" parts in the production line due to various reasons. People have torn down older motors and found parts in them that weren't supposed to be there; ie. finding sti pistons, rods, or such in a non sti block. I guess there has been instances where they ran out of parts on a production line and had to use the next runs parts or even dip into the sti parts bin to complete production.

10-10-2010, 12:09 AM
Interesting read. Thanks for the info Greg.

10-10-2010, 08:15 AM
Your welcome John. The main reason of course for me doing this is my Outback XT build. I kept hearing my Outback had pretty much the same engine as the STI, and then I also heard it wasn't.
What I found out was, in the year I purchased mine, it was the same. Furthermore, because I have 138000 on my Outback now and some day I desire to do the STI drivetrain swap I wanted to make sure I didnt need to do the engine as well.

Whenever my engine needs swapped due to the miles I was looking at having mine rebuilt or swapping for a EJ257 etc. etc.

Now I know I can pull it out and either, try myself, or have someone else rebuild it, and I dont need to find an STI block and heads somewhere. The crank, rods, piston, cams will likely be replaced :D but if I can save money because I basically already have an STI engine, then there is no need to waste money on those parts.

My car runs great and I am not having any problems with it at all. My goal is at least 250000 if I can do it, but I wanted the info just in case the day comes that I lose a ringland or something goes.

Also what this does is allow guys with WRX or later legacies who want the STI engines, to have another place to look in older Legacies and Forresters.

10-25-2010, 02:50 AM
This was one of the most informative threads I've ever read. This affirms my love for the 05-06 LGT.

05-19-2011, 11:15 PM