Ok a few months back we had an individual asking what would be involved in making your own 2.2L stroker kit. Well with some odd happenings I was able to join in and try this out myself. I have had several questions through the pm chain and emails and such. Now granted I have had the engine together and tore back apart 4 times now because this was a big trial and error type thing. Luckily for me the errors were not anything major and most of the time the tear down was for modding again. Now this is not super kit this is not something that you should do on your own you will need help and patience and about 2~3k to spend. With that said here is what I did.

1. EJ20G closed deck engine (Does not have to be this engine I used it for the overall strength of the block)

2. 2.5L JDM Forester STi crank: New here in Japan this is $500 stateside I dunno

3. Rods: believe it or not your EJ20G,K, and 207 rods will work fine price should be nothing since yours are fine or you can upgrade this will be added cost to what I already posted above

4. Pistons: This is where it gets tricky. The standard stroke on the EJ20 is 75mm I assume we can all agree it is pretty much this or close. This is what I go by, Jun goes by, and HKS goes by. The standard stroke for the EJ25 is 79mm which of course brings you to the thought "Uh thats 4mm stroke up you can't just use a head gasket to cure it". No you can't but you can buy custom made pistons and have them professionally shaved. Now if you get some that have a 6mm head and you shave 4mm your gonna start thinking about reliability issue due to the now very thin 2mm piston head. Also you will have to shave your piston skirts as they will be ever so slightly in the way this is a 2~3mm shave on them. Or you can buy the HKS pistons which are already made with the extra 4mm in stroke because their kit adds 4mm in stroke. There may be other manufacturers that make pistons like this. Average cost for premanufactured is anywhere from 750~1.5K

5. P&P your EJ20G heads save some cash do it yourself if you have the skills and trust me they work great once this is done.

6. Headgasket I went with a 2.0mm but a 1.8mm will work fine this will cost about 2~300.

7. Seal kit this is your standard overhaul kit (main bearing seal valve cover seals etc) this will run you anywhere from 2~300.

8. Bore the block now I don't know what the standard running price is on this nor do I claim to but for the most part its relatively cheap.

Now if your mechanically inclined and have the tools you should be able to slap this baby back together and go about your standard ECU tune and such.

If you have questions please feel free to ask if you have suggestions please post em as I am always game to try something new.

How did you get a phase II crank to work in an old phase I engine? The only way I see this being economical is if you could use all stock subaru parts with no machining....but thats not the case. 2.5l STi short blocks sell for less then you can put a smaller displacement stroker engine together for. If for some reason you wanted to make a stroker engine, a better block to start with is the EJ22t block.

The early EJ25 dohc engine have a phase I crank that drops into a EJ22t with no machine work but the rods have a smaller BE journal(makes them specific to that crank) and are slightly longer so cutting the top of an EJ22t piston is basically out of the question. I have all the parts needed to put this engine together, maybe some day I will and see what power I can make on cut pistons before it blows. ~4mm off the top of a turbo piston is nothing to sneeze at! I am sure I could make one hell of a NA engine with the 2.5l crank in a EJ22t using slightly cut NA piston with about a +1.8mm deck height(2mm HG) and some cut EJ18 heads. easy 13:1
EJ20 with EJ25 crank= 2.15L
EJ22 with EJ25 crank= 2.35L

Steve,
The only machining that has been done to the engine is boring out the block to a 92.5mm. The crank sits right down into the EJ20G and the rods from a ver 7 fit perfect as well. This is just what I did and the approximate cost for doing such a thing. If I wanted to do the EJ22 I would have made it a 2.3L Kit. Also I used the HKS 2.2L Kit pistons so how in the hell is it a 2.15L??? I am assuming every numb nutted wannabe manufacturer is better than Jun and HKS?? Not hardly and I am not an JDM guy only but Jun slapped down over 500 a good while before anyone stateside did it.

Oh and steve the phase II crank sit down in the phase I closed deck block like it was ment for it. For rods the Ver 7's mount right up to the crank. So by going with HKS pistons the only maching required is the block!!!

How is that possible...the thrust bearing is in a completly different spot?? You bored your EJ20 to fit EJ22 pistons??

Dirty block is a phase I with thrust bearing in the center
Clean block is phase II with thrust bearing at end of block, no way will a phase II crank work in a phase I block without machine work....unless you plan on running it without a thrust bearing:lol:

http://home.epix.net/~smf52/74209615.jpg
http://home.epix.net/~smf52/casehalve123.jpg

I will post some pictures in a few days Steve trust me man your not gonna believe this!! Also is there a possibility that the EJ25 used in the STi forester is different than the USDM STi???

I will post some pictures in a few days Steve trust me man your not gonna believe this!! Also is there a possibility that the EJ25 used in the STi forester is different than the USDM STi???

Not a chance. I have no doubt the Phase II crank will physically fit in a phase I block....without the thrust bearing in place. The only problem is the thrust bearing. The phase I block is machined in the center for the thrust bearing as you can see circled in the first picture(bearing not in the journal). The phase II is machined closest to the flywheel as you can see in the picture(bearing in the journal) big circle.

If you are using a phase II crank in a phase I block the thrust bearing has to be on the last journal(closest to flywheel) the problem being the Phase I block isnt machined for it. I have heard of people machining the phase I blocks to fit a phase II crank.

It wont and cant work without machining the old phase I block!

The reason I am asking is because when you order the crank its the exact same part number as the N/A EJ25 over here. So I am not sure what differences there are if any. Also I am not doing this alone I am not THAT good (wish I was) I am having the help of Naramasa Speed and MSpec. I will definately get some pics up as soon as I can. Everytime I go to work on the car I forget the digital camera!!!

Oh, and you can't use the 2.0 rods. The extra 1.2mm in length of the short stroke rods will put the piston right out of the block. You need to use EJ25 rods to match the crank.

Sounds like you have quite a bit more research to do. Yes anybody can build a stroker with stock Subaru parts, but you HAVE to have the right parts, not a hodge-podge of parts that may "fit" but don't really fit.

Well if your getting custom pistons you can use 2.0 rods...although i agree the 2.5's are better for a few reasons.

My thanks to Scoobie Steve for the info on the thrust bearing. My apologies for being somewhat of an arse.

As for the rods I hate to tell ya buddy but the WRX RA rods work perfect with the Crank and HKS Pistons!! I have no clue what your talking about extra 1.2mm in lenght or stroke or whatever but the pistons are not leaving the block!!

http://img141.exs.cx/img141/5364/tomeicrank5xk.jpg
http://img141.exs.cx/img141/3871/block8fw.jpg
http://img141.exs.cx/img141/1679/bore8au.jpg
http://img141.exs.cx/img141/4651/hkspiston6oa.jpg
http://img141.exs.cx/img141/2403/pistoncomparo0mf.jpg
http://img141.exs.cx/img141/3581/pistoncomparo27sq.jpg

Updated post above!!

Ahh, I see. You're using HKS stroker pistons. Not sure how I missed that. I'm not familiar with the HKS slugs, but are you sure they are designed for the short rods and not the long rods? I think the stroker pistons I've seen were made to be used with the longer 2.5L rods (131.5mm for 2.5 vs. 130.5 for 2.0 IIRC) If you're deck clearance was off by 1mm your CR might be a bit low! Whats the compression height on those pistons btw?

Otherwise if everything specs out it should make for a nice motor :)

Ok don't shoot me here but the full HKS stroker kit to include the crank has a 4mm increase in stroke. The pistons are made 4mm shorter in height to compensate for this. HKS said a 1.4mm head gasket gives 8:1 compression but I will not have complete results until later this week. This has been a year long thing and I have not really driven the car much because of the constant changing of parts.

Hey,

Great info guys. I am thinking of going this route instead of just swapping in a ej257 block due to the compression issue and the ej22 looks like it should be a much more solid platform handling boost. Please correct me if I am wrong with this
EJ22t block + phase one 2.5rs crank + 2.5rs rods + 4mm shorter pistons equal= 2.35l
Trying to get a good idea of everything needed and to source parts and price to determine the best buildup

Thanks for the information
Nicholas

The pistons aren't 4mm shorter. But you have the general gist of it. If you have a total of 4mm increase in stroke, only half of that will be on top of the stroke, so roughly you need 2mm shorter pistons. But, if you use the EJ25 rods, which are ~1mm longer than EJ20/22 rods, you need pistons that have about 3mm less compression height.

The Wiseco EJ22 -> 2.33L pistons have a compression height 30.25mm (measured from the center of the wrist-pin to the top of the piston)

The normal EJ22 turbo pistons have a compression height of 33.25. So the difference between the two is 3mm. The stroker pistons also have a larger dish to make up for the increase in static compression as well. If you stroke an engine an maintain the same dish and deck clearance, you'll get an increase in compression ratio since the TDC combustion volume is the same, but the BDC volume has increased. The pistons need to account for this as well.

Nick I don't know much about the 2.5 in the RS but if your going to build an engine I would try and get forged internals thats if the RS does not have them!!

Hey,

Thanks for the response and the technical descriptions. I need to make a couple of corrections on some search information that I have found.

EJ22t block + wrx heads + wiseco offset piston kit + EJ20 forged rods(eagle or scat etc..) + phase one 2.5rs crank + EJ22t head gasket = 2.330liter

I found a chart that outlined some subaru builds and this one seems to be exactly what I am looking for. A touch more displacement to a mild increase in torque but a very strong engine that can handle plenty of boost

Please let me know if I am missing something or need to make some other considerations for parts.

Thanks for all of your help
Nicholas

EJ20 rods WILL NOT WORK ON EJ25 PHASE I CRANK. :)

Hmm then I assume the Forrester STi crank is a Phase II because the EJ20G RA rods work just fine.

Hmm then I assume the Forrester STi crank is a Phase II because the EJ20G RA rods work just fine.

Yes the STi forestor is a Phase II ej25 crank. Phase I EJ25 crank only came in 96-98 2.5l engines. Phase I EJ25 cranks use a smaller BE journal. The only rod that works with them is a Phase I EJ25. There are companies that make after market rods for this engine. I covered this all in an earlier post ;)

Yes the STi forestor is a Phase II ej25 crank. Phase I EJ25 crank only came in 96-98 2.5l engines. Phase I EJ25 cranks use a smaller BE journal. The only rod that works with them is a Phase I EJ25. There are companies that make after market rods for this engine. I covered this all in an earlier post ;)

Do you know the exact dimensions Steve? I've long said this was the case, but since I've never much cared to find exact figures I only theorized they were ~4mm smaller - which would offset the rodjournal centerline 2mm, giving a total stroke increase of 4mm. My guess is they just offset ground 75mm stroke cranks down to get the 79mm?

So what happened?

So what happened?since you brought this back....

What are the CC's on those HKS pistons?Make of those heads(year)? and head gasket you ended up using?