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Old 08-09-2007, 01:21 PM   #26
ralleydriver
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Hello all,
Just want to clarify,
Will the EJ257 Sti S/B work with my stock MY99 SOHC heads. This will be in preperation for boost in a few month. You seem to be the only thread that has good clear information so any info would be greatly appreciated. thanks Craig J
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Old 08-09-2007, 03:25 PM   #27
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Quote:
Originally Posted by ralleydriver View Post
Hello all,
Just want to clarify,
Will the EJ257 Sti S/B work with my stock MY99 SOHC heads. This will be in preperation for boost in a few month. You seem to be the only thread that has good clear information so any info would be greatly appreciated. thanks Craig J
Yes the Ej257 will work with SOHC heads. I wouldnt recommend stock however, i would recommend at very least new springs and retainers, (TWE makes a nice setup), as well as a turbo cam (also TWE) the combination of those 2 things and the sti short block will make you very happy, even though with the even the stock cams the car has power it will tend to run out of power past 6000rpm where as with a turbo cam you can make more power uptop.

Quote:
Originally Posted by kaos200 View Post
Specs
EJ257 with SOHC heads approx 8.4:1 (since the sohc has 3cc more volume then the wrx heads according to Cobb)
EJ257 with WRX heads approx 8.6:1
EJ257 with STi heads approx 8.2:1.
the only thing i see wrong with this is actually that the EJ257 w/ the SOHC heads is closer to 9.0:1 the exact CR I'd have to look up but i kno the combination of the RS SOHC heads and the STi block is just under 9.0:1
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Old 08-09-2007, 05:24 PM   #28
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Quote:
Originally Posted by subiekid View Post
What about with 2.5 DOHC heads? I searched and found tons of threads, but all of them seemed to be for using wrx heads.
Whats the verdict on the MY98 DOHC heads as far as comp ratio?

Anyone find out?
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Old 08-13-2008, 11:35 PM   #29
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I know this an old thread but I'm about to go with an STi s/b into my 05 RS. I plan on using the RS heads. Is there an updated list of what you have to do to make it bolt up or is the same as for the older RS's.

I'm also looking for some suggestions for E.M. I was using e-manage and my stock ECU but I'm thinking about going with a standalone for the new setup.

And what is the actual C/R with SOHC heads...is it around 9 or is it 8.4 as the O.P. stated?

Sorry for all the questions just trying to get all the facts before I start this build
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Old 08-17-2008, 07:37 PM   #30
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I think that he was right about the 9:0:1 cr because n/a RS's are running high cr anyways and when slapping a sti s/b to rs/wrx heads your bumping the cr up anways. just my .02. just to let you know im in the process of building my hybrid swap also. im using wrx heads though.
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Old 08-25-2008, 01:33 PM   #31
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SOHC heads and an EJ257 shortblock aren't really a good idea.

The valve reliefs are in the wrong position.

The compression ratio is 8.94:1 with the STi headgasket. (SOHC 51cc)
If you use the Cometic .040" gaskets, you'll have a CR of 8.57:1. This helps the compression ratio issue and also helps give you more room between the valves and pistons. With that, you could probably get away with the EJ257 shortblock.

Best thing to do is get an STi block and get the right pistons.

DOHC RS heads would give a CR of 9.42:1 with the STi headgaskets and 9.0:1 with the .040 Cometics
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Old 08-25-2008, 02:33 PM   #32
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I'm assuming the DOHC RS heads are the same as the Legacy 2.5 NA heads which I have measured as 46cc?

There is also the 1 year only 96' 2.5 NA DOHC heads from a legacy that have a larger combustion chamber of 57cc which is close to what the stock sti heads are, so you can use the stock sti bottom end with stock pistons and stock sti head gasket and end up around the stock sti CR. These heads are hydraulic buckets which are self adjusting and are not adjusted using the shims.

I have a set that I plan to rebuild and use with my sti short block i bought used.
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Old 11-26-2008, 06:13 AM   #33
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this idea has been bouncin around in my head for awhile. crawford sti sb with wrx head port/polish with brain crower cams. ported and coated intake manifold and maybe sugetions on the throttle body and hydra.

all in a 99 rs for n/a build for something different. pretty much a hybrid build but no turbo
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Old 08-19-2009, 05:32 PM   #34
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Bumping up an OLD thread...

Assuming the EJ257 and SOHC have a CR of 9.0:1... Would running the stock ECU still work? My question is for EMISSION purposes. Basically, if I remove my standalone and plug in the stock ECU, would the car pass emissions through OBDII?

Thoughts?
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Old 08-20-2009, 05:24 PM   #35
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The ECUs on both my 98 and 95 Legacy were just fine with the EJ257 swapped in, once I addressed the CELs that had nothing to do with the block swap (dead O2 sensors, etc.) And this car originally had the EJ22 even, with a head swap to the EJ25. It should be within the tolerances of the ECU, assuming you're not running so much boost that you've thrown some other parameter out of whack (like MAP/MAF)
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Old 08-20-2009, 05:29 PM   #36
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Great! The idea would not be to boost under the stock ECU, but rather to run it in vacuum for a couple of days so that the OBDII readiness codes clear, and I can pass emissions. Once this is done, I can switch back to the standalone ECU, and bigger injectors.
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Old 11-29-2009, 02:44 PM   #37
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so everyone doin this swap (well the majority) is doing this for an n/a set up??? i dont understand y not build the stock block for n/a.....but i am looking into this hybrid for my rs and just gathering info.....

was wonderin if i could get more info from Dom'sGurl though on y this isnt such a good idea for a hybrid,

also if thoes boosting on this set up can give some feedback on how well it works and any issues to look out for and all that good stuff

(sorry to bring up the old but its all ive been able to find searching
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Old 10-17-2010, 12:14 PM   #38
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Im new to the Nasioc forums and was wondering if i wanted to buy a Turbo kit for my 2004 RS with 125k miles on it. What would i need to upgrade inorder to run a turbo safely?

Im already considering to buy a thicker head gasket to lower the compression ratio, but what head gasket should i buy and what else should i look to invest in?

My budget isn't too high but im willing to invest alot long term.
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Old 10-17-2010, 12:27 PM   #39
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2004 RS internals are weak and the rods fail around 300whp. This means you should keep the boost down around 6-8psi.

Currently you're at about 10:1 CR. If you swap in the STi block you'd get about 9:1. If you swap in an EJ255 block (that was mated to D25 heads previously) your CR would be 8.4:1 with OEM STi head gaskets. This is more ideal. The EJ255 and 257 have the same everything except pistons. Both are equally as strong. With that setup, you can run whatever boost you want as long as you add valve springs to your heads. Not adding springs will float the valves around 8psi and 6k rpm.

So the big things are:
Valve springs
Proper Shortblock.

after that you're good to go and have a lot of fun.
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Old 10-18-2010, 04:33 PM   #40
Powder61690
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Ok...so i just need to spend about &2,000 for an EJ257 short block and im set to run high psi if i upgrade the valve springs? and is the EJ255 a better block than the 257?

Also, whats you opinion about the universal turbo kits that come with the oil coolers, inter-coolers, blow-off valves, etc.? Will they last if it's not run at a high psi?
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Old 10-18-2010, 05:17 PM   #41
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Old 10-18-2010, 07:02 PM   #42
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you're about to make some big mistakes.

Do not buy a kit like that. it doesn't come with any exhaust work. The pipes are generic and not designed for the car. If you're going to use ebay get a CXRacing intercooler for a wrx. The pipes need some serious massaging, but the core is solid and it comes with t-bolts and couplers that work.

Then have someone make you up and down pipes combined with a borla (or equivalent) header. Weld a bung in your oil pan for the oil drain and call it good.



Use an EJ255 block out of an 06-09 WRX. That is the right one. The EJ257 block won't be good for what you're doing.
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Old 10-19-2010, 07:28 AM   #43
Powder61690
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Alright thanks. Is the CXRacing intercooler a full Kit or just the intercooler and also can't i just use any brand of subaru turbo headers on my RS? I thought they were interchangable.

What do you mean by weld a bung in oil pan? Would the new EJ255 short block not have an oil drain plug?

Also if you could help me find a Link where i could buy an EJ255 because i search for it and all i find are forums.
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Old 10-19-2010, 02:42 PM   #44
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Quote:
Originally Posted by Powder61690 View Post
Alright thanks. Is the CXRacing intercooler a full Kit or just the intercooler and also can't i just use any brand of subaru turbo headers on my RS? I thought they were interchangable.
Full kit.

If you get other headers the flange to the up pipe points up. So no, they aren't interchangeable.


Quote:
Originally Posted by Powder61690 View Post
What do you mean by weld a bung in oil pan? Would the new EJ255 short block not have an oil drain plug?
you need an oil drain from the turbo.

Quote:
Originally Posted by Powder61690 View Post
Also if you could help me find a Link where i could buy an EJ255 because i search for it and all i find are forums.
I don't have an online store for that.
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Old 10-19-2010, 10:21 PM   #45
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Quote:
Originally Posted by Maxwell Power View Post
Use an EJ255 block out of an 06-09 WRX. That is the right one. The EJ257 block won't be good for what you're doing.
Y do u say this......it was my understanding that the block was the same 255-257 but the internals that differed....in which case y go weaker no matter what Ur output goals??? I personally would earner have a block "too strong" then find myself miss calculating, or have a situation where overboost occurs...or even have a change of plans down the road leading me to have to then buy what I could have bought in the first place.....

But again this is based on the understanding that the blocks are the same semi closed deck blocks......
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Old 10-19-2010, 10:49 PM   #46
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Quote:
Originally Posted by Dori Ninja View Post
Y do u say this......it was my understanding that the block was the same 255-257 but the internals that differed....in which case y go weaker no matter what Ur output goals??? I personally would earner have a block "too strong" then find myself miss calculating, or have a situation where overboost occurs...or even have a change of plans down the road leading me to have to then buy what I could have bought in the first place.....

But again this is based on the understanding that the blocks are the same semi closed deck blocks......

do yourself a favor and do a little research before you make a post like this.

http://forums.nasioc.com/forums/show....php?t=1667168
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Old 10-19-2010, 10:50 PM   #47
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Quote:
Originally Posted by Maxwell Power View Post
The EJ255 and 257 have the same everything except pistons. Both are equally as strong. With that setup, you can run whatever boost you want as long as you add valve springs to your heads. Not adding springs will float the valves around 8psi and 6k rpm.
From a few posts ago....
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Old 10-20-2010, 12:06 AM   #48
Dori Ninja
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Quote:
Originally Posted by Maxwell Power View Post
do yourself a favor and do a little research before you make a post like this.

http://forums.nasioc.com/forums/show....php?t=1667168
y?? u still havent answerd my ??? i was wondering y to told him to opt for the 255 over the 257 and putting down what i know...not saying tell me the differences but y u would recomend the block from a lesser model than that of the greater...but that looks like a great read and i will enjoy it!!
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Old 10-20-2010, 12:07 PM   #49
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http://www.maperformance.com/crawfor...aru-s0114.html
http://www.cosworthusa.com/store/pc/...&idproduct=364

What if i saved up to buy these? would the head and short block be able to connect correctly?
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Old 10-20-2010, 12:30 PM   #50
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Quote:
Originally Posted by Maxwell Power View Post
If you swap in the STi block you'd get about 9:1. If you swap in an EJ255 block (that was mated to D25 heads previously) your CR would be 8.4:1 with OEM STi head gaskets. This is more ideal. The EJ255 and 257 have the same everything except pistons.
I already posted the reason why. READ MY FRIEND! It's right there.

THAT IS WHY!
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