Need a shortblock, please help me understand 255 vs 257

I'm unfortunately in need of a new shortblock and I've been attempting to understand the similarities and differences between the 255 and the 257 but I'm still a bit unclear and was hoping one of you gurus could give me some advice.

My car ('05 LGT 5mt) is currently unmodified and I have no intentions of doing anything major in the future so I'm guessing that replacing my shortblock with another exactly like it would be just fine for me but if I have the opportunity to upgrade for little or no added cost then naturally I want to do that. I guess my question is quite simple: what is the best shortblock for me to buy and run using the stock tune and hardware?

I can buy at wholesale through my local dealer but just for my own reference I was looking at subarupartsforyou.com and I see different part numbers for 04-06 Legacy, 07-09 Legacy, 07 STi, 08-13 STi and so on.

Your knowledge and assistance are deeply appreciated.

You can order the ej257 and the gasket set for a 2005 that's what I did.

The ej257 is aboput $200 cheaper then a ej255. They say it has a better crankshaft. You will get the current version of the ej257.

http://legacygt.com/forums/showthrea...-r-184106.html

There's my thread.

Thanks Max. So am I correct that the only difference between the two is the crank? I've read that the pistons are different resulting in a different compression ratio and then of course I've also read that there's little to no difference in the CR. I guess that is the part I'm most concerned about.

For 2005 and 2006 LGT's, there is no difference in short block with an STi motor from 2004-2006...even the pistons are the same. They share the same part number. My understanding is Subaru has changed the part number a few times over the past few years as revisions were done to the short block. The most current part number right now is 10103AC030. If you search that part number on a vendors site from this forum (infamous, heuberger, fred beans, boston motorsports, etc) you will see that it is the same part number for both an EJ255 and EJ257. You can also google Subaru parts, open a link into one of the results for OEM Subaru parts, punch in that number and get both EJ255 an EJ257 to come up.

The 08+ ej257 have a nitrided crank and other than that the differences are minimal if at all. None of which should deter you from thinking one is better than the other. You only begin to see differences if you get a longblock s the newer ones have DAVCS where our motors have SAVCS and you have you have to re do some wiring and other little things. Thats why people just get shortblocks and put their LGT heads on and call it a day.

Originally Posted by Serb Legacy GT

For 2005 and 2006 LGT's, there is no difference in short block with an STi motor from 2004-2006...even the pistons are the same. They share the same part number. My understanding is Subaru has changed the part number a few times over the past few years as revisions were done to the short block. The most current part number right now is 10103AC030. If you search that part number on a vendors site from this forum (infamous, heuberger, fred beans, boston motorsports, etc) you will see that it is the same part number for both an EJ255 and EJ257. You can also google Subaru parts, open a link into one of the results for OEM Subaru parts, punch in that number and get both EJ255 an EJ257 to come up.

^^^^^ This. Search threads from Unclemat, he used to loose his mind over this.

The part numbers I'm finding are 10103AC030 for 04-06 Legacy, 10103AC040 for 07-09 Legacy, 10103AC050 for 08-13 STi.

Originally Posted by tlfowle

The part numbers I'm finding are 10103AC030 for 04-06 Legacy, 10103AC040 for 07-09 Legacy, 10103AC050 for 08-13 STi.

http://www.trademotion.com/parts/ind...&siteid=214857

Here is a quick search to show you that the EJ255 and EJ257 are the exact same short block. For your application, a 2005 Legacy GT, you want to use part number 10103AC030. Use the link and scroll through, and you will see that part number comes up for an '05-'06 LGT (Spec. B too), '05-'07 STi, '05-'06 Baja Turbo, '06 Forester XT, and '06 Outback XT. All of these share the same short block, there is no difference. The heads and intake manifold may differ between the models, as well as what turbo comes stock with each vehicle, but the short block is the same.

Order a 10103AC030, whether it's an EJ255 or EJ257 doesn't matter, and have your heads re-finished and put them on the new block. I would order from one of the vendors here in the LGT community...best service, best prices, and you support one of our guys

the new short blocks have a heat treated crank not nitrated as of this last year

Originally Posted by tlfowle

The part numbers I'm finding are 10103AC030 for 04-06 Legacy, 10103AC040 for 07-09 Legacy, 10103AC050 for 08-13 STi.

The differences between 255 and 257 are basically in name only - the year is more important. The two Legacy part#s only differ in pistons. The early block is designed for the larger B25 heads, the latter for the smaller D25 heads. Thus the later pistons have more dish to keep the same compression ratio.

Just my $.02 - I would strongly suggest that if you are going to spring for a new shortblock and have any future performance desires get a block w/ 4032 forged pistons and the bearing clearances blueprinted. Yes, you will spend a little more than new from Subaru but you'll have a better platform to work from for future mods. The 4032 pistons (Mahle, Wossner, Cosworth) are very streetable but will hold up better to performance mods since they are less brittle than the stock cast pistons. Bearing clearances are a crapshoot in even new Subaru blocks - maximum reliability is when all of the clearances are the same.

Sorry for the level of detail - I'm in the middle of building a motor and have been through every possible combination to make sure it is build right.