hmm i recommend you getting a complete wiring harness and running motor.

Since you have a GD everything will swap in easily with no extra wiring and making you smog legal.

If you must build a motor, at least get matching harness, ecu, and heads with the ej255/ej257 shortblock.

If 06+ wiring make sure you obtain matching keys, transponder, and ecu.

AVCS is nice to have 06+ ej255 or ej257 have avcs intake side. If you really want to do a "swap" 08+ have dual avcs but some minor wiring will be involved, not to mention a nice nitraded or heat treated crank with better oil passageways depending on the year.


Not only will this save you money, it will save you the headache of figuring out what went wrong.



For drivetrain don't waste your money on anything else other than a complete 6 speed swap

 

sweet. thanks for the info bro. not knowing what ACVS were before your post, i did a quick research and may stay at the single intake side. it seems to be a lot more wiriring to see that secong ACVS.

in terms of "mix n matching" i am still trying to understand all these numbers on this block. i know its an EJ25 semi closed. also says "B25C 703" does that mean its one of the newer motors? also, the diff beteen EJ25 and EJ257, EJ255 is genereation, correct? EJ257 came on newer cars?

again, thanks for the suggestions and heads up.

 

Primary Difference between a WRX EJ255 and EJ257 shortblock are the pistons. 257 has a shallower dish measured in CC, where the 255 has a deeper dish. This is because of the head differences. EJ255 longblocks run D25 heads (except for older Legacy EJ255) which have around a 50cc combustion chamber. EJ257 have B25 heads that have around a 55-56CC combustion chamber.

Basically, for a car that run on pump gas, you do not want to slap D25 heads onto an EJ257 block as your CR will be up around 8.8-9:1

Now if you are building your block, and plan on putting in forged pistons, it does not really matter. You can choose a piston with a dish CC appropriate to your heads.

 

ah. great info. thanks bro. im trying to build up my STI engine to OEM specs. or as close to it. so, i can run EJ257 heads as long as i use the respective pistons? the shortblock has nothing to do withthese numbers? and how would know which heads came on my short block when all that is stamped is: "EJ25"? B25C it also says. based on recently learned info from you, this block was factory built with the B25, EJ257, 55-56CC heads, correct?

 

I do recommend getting complete wiring

yep!



the ej255 has pistons that bump it .2 cr, the heads are nearly identical studies shown b25 head is the best(refer to aboothman's post).

Any how you build it, get the complete wiring for either a 06+ wrx or sti. Use the corresponding ecu, transponder, and key. So you can just plug in a accessport and get a tune for w/e mods you are doing.

A brand new 08+ shortblock with the nitraded crank or heat treated crank is around 1800. (you can choose to drop in some nice pistons or not)

This way it is most reliable for around 350-400 whp, any crazier build becomes reliablity issue if you do track hard.

Then finding a pair of heads that are still good would be the challenge, thus me recommending you to save that shortblock and finding a complete long block out of a running car. Which includes turbo exhaust manifold etc etc.

 

Im in no rush to build this engine. I dont mind picking up a set of heads, realizing they are no good and looking for another set. With this build, id like to stay as close to stock power as possible. and yes, when i get to the chassis portion of the swap, eveything will be replace (wiring, ecu, cluster, sensors, driveline, etc) its essentially a whole different car in my 02 bugeye RS body. it WILL take a bit of time, which i am fine with.

So, for my STI shortblock, im looking at running the most reliable setup. Even if this means going with the slightly lower CR.

also, now this is getting at me. does B25C indeed signify that I had the B25 heads on there?

 

my block says b25C also but it is from an 06 wrx ej255

If you have the time and money to do it, I suggest avoiding splitting the block and hone and match a good set of pistons with arp head bolts with oem sti gasket. That is why I recommended a brand new 08+ shortblock and swap the pistons out since it comes built with a awesome crank.

 

ah. hmm....i still need to do some more reading. LOL. thanks for all the info guys. deff have learned a lot in just these few posts!

 

Btw what is the casting number? 702? 703?

 

703. what does that signify? i know that AB, AA, BB letter and numbers are the bore for each respective cylinder. correct?

 

the Newer EJ257 Subaru cylinder block castings vs. the previous 702 EJ257 cylinder block casting.
The casting quality difference is night and day!
(703) Casting is the newer latest and greatest cylinder block casting.
(700- 702) Castings were used for previous model years.

All internals appear to remain the same.

 

Sweet! Thanks again for all the info. I thinks its safe to say I now know my shotblock. Lol. So in terms of the heads, I can run either 255 or 257 as long as I use the respectiblve pistons for my application? (Strength and reliability in terms of CR)

 

They discontinued the Nitrated crank. They are all heat treated on any new shortblock.

Installing pistons without splitting the block is a bad idea and pretty much impossible if honing is done (which it SHOULD any time pistons are installed). The block needs to be thoroughly cleaned after a hone. Putting in pistons without measuring and honing to the specific pistons is a sure way to have an oil burner. Better to stick with an OEM block and solid tune in that case.

The block generally has no indication of the heads that eventually go on it as the same engine case is used for EJ255 and 257.

Buy once and buy what will work. Wait until you have $800 or so and buy a clean set of heads with NO issues. Ready to bolt on, cleaned and inspected by a shop, etc.

Yes, yo do





All good advice Flatironstuning.com in Colorado has great prices on OEM short blocks and ships for around $75 IIRC. Heads can be found if you are patient, but it is very well may be trouble than finding a good longblock ready to go as he said. And with an OEM longblock you probably dont have to worry about mating the right heads to the right pistons...

As for the wiring, if you are not set on 05+STI or 06+ WRX, look into 04 STI. Same engine etc but no immobilizer to worry about. Not a big deal as long as you do what he said and get the key, immobilizer, ignition and ECU from the same car...but 04 STI makes it a lot easier. Easier to steal too tho...

As for B25 vs D25, I did not necessary mean that B25 are better, but that is a subjective argument. It is commonly held that the D25 heads have better combustion chambers, and flow slightly better, but they cause CR issues unless you have the proper pistons. I guess I should have said they are less of a hassle as most aftermarket pistons are made for a 55-56CC B25 combustion chamber.

A lot of these topics are current and past issues that are debated on NASIOC and other places. Mostly by people with goals much loftier than yours.

You have the idea, but you should stop thinking about heads in terms of 255 or 257. That is generally a number associated with the combined longblock. D25 = smaller combustion chamber, so it needs pistons with a bigger dish. B25 = larger combustion chamber, so pistons need a smaller dish.

Shoot for 8.2-8.5:1 CR in my opinion.

 

AHHH! my eyes! sooo much info! thanks again guys. this really helps. I have indeed browsed, read, and studied many threads and articles regarding this build. I just wanted to start my own thread with my own questions and answers.

Ive gotten a general idea about the relation with the block and heads. id say im 20% comfortable with head terminology and mechanics. i understand the general idea regarding CR. it seems that with the two different head and piston setup ups, Subaru tried to maintain that CR between the two heads?

im still reading around and watching many videos regarding this topic. im a true gearhead at heart and want in it to win it. i plan on building my heads myself as well. I will also learn a bit more when I have my RS heads on my bench. (blown pass side HG. going to R+R HG's, stem seals, and possibly valve job if neeeded)

Wiring: jeez. i dont even want to think about that just yet. lol. but i do know i need to correlate between engine and computer.

this is all great info guys. i really do appreciate it. Im going to focus on longblock assembly for now and return/revive this part of the thread once i start looking at installing heads.

 

astonishing that you can learn so much from playing GT5