EJ257 into 2.5RS Faq

[kaos200]

making this for all the newbs


Specs
EJ257 with SOHC heads approx 8.x:1 (since the sohc has 3cc more volume then the wrx heads according to Cobb)
EJ257 with WRX heads approx 8.x:1
EJ257 with STi heads approx 8.x:1
EDIT: I HAVE REMOVED THE CR ESTIMATES SINCE THERE ARE NOW MANY VARIABLES (EJ255, EJ257s, and differences in cylinder heads).

The block is good to atleast 7500rpm (from personal experience, others may go higher, im not that crazy)
The block is holding up to 20+psi boost, and 450whp so far without much trouble (again, its all in the tuning/setup)


If installing into RS with sohc. parts needed are...
- STi headgaskets

-WRX upper coolant pipe... requires the following
-- coolant line from pepboys/kragen to go to heater core, stock prerouted piece will not work
-- you need to grind some metal off the passenger side cylinder head near where the upper radiator hose attaches to the upper coolant pipe. A die grinder makes quick work of this.
-- you need to lengthen the wires for the coolant temp sensor, since it sits in a different location.
-- you need to do the coolant through throttle body bypass mod, AND remove the little piece of metal that sticks into the throttle body that the coolant goes through, or else it will hit the new upper coolant pipe where it meets the heater core hose. (yank out or cut off, your choice)

OR, use the stock upper coolant pipe, but you need to measure where to cut out a chunk of it since the block has that extra breather, then weld the hole in the pipe shut.




If installing with dohc,
You can use either upper coolant pipe, and if using the one meant for the wrx, you do not need to grind the heads, but the other mods must be done. INCLUDING....

-DOHC Oil dipstick tube, it mounts to the head differently.

-You still need the STi head gaskets.

If using wrx heads, you can use the stock RS intake manifold, and everything else but you must drill out the manifold bolt holes, and shave some of the plastic on the driver's side valve breather piece (hard to describe, black plastic piece that attaches to top of valve cover, well, guess its not THAT hard to describe)

If using STi heads, you MUST use the sti/wrx intake manifold, and rails etc. I had an adaptor made to use my stock RS throttle body, but that was such a pita
So using STi heads, pretty much means you've gone and changed the entire motor setup, and you're going to probably do an ecu swap as well.

If im missing anything just post it and Ill add it so people doing a search can just find it all here.

EDIT: SOMEONE ASKED THE FOLLOWING:

So. Are you saying that if you use wrx heads in an rs that you do not have to do an ecu/harness swap? Just em?

No, if you switch from SOHC to DOHC, you must change the ecu somehow. Either do a wiring swap and go OEM or use a standalone system.
That being said, I had moved away from recommending piggybacks and standalones years ago. I've done so many wiring mergers for people now it's not even funny. Another benefit of that is that for those in smog strict states (like good ol' CA) the swap would be legal.

EVERYONE NOTICE THE ORIGINAL POST WAS FROM 2004!
I INTENDED IT FOR GC MODEL 2.5RS, NOT NEWER MODELS.

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[kastle]

adding this to the Forum FAQ... good job

[subiekid]

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.

[kaos200]

I havent had a chance to experiment with them, but I would imagine the only difference is in the intake manifolds. You would need to just use the manifold for the dohc RS, and not the wrx.

[HndaTch627]

great post Kian, i am gonna fly you out here when it's time to put one in liz's car

Jeremy

[kaos200]

haha, thats cool, I wanna come visit eventually anyways!

[HOK]

awesome post!

[Crawford Performance]

Originally Posted by subiekid

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.

I have put the 2.5 n/a DOHC heads on the STI shortblocks many times.

Use the STI head gaskets and every thing else bolts up.

Quirt Crawford
www.crawfordperformance.com

[latinskllz]

Originally Posted by kaos200

If using wrx heads, you can use the stock RS intake manifold, and everything else but you must drill out the manifold bolt holes, and shave some of the plastic on the driver's side valve breather piece (hard to describe, black plastic piece that attaches to top of valve cover, well, guess its not THAT hard to describe)

How much do you need to drill out the bolt holes? do you have any pics showing this by any chance??? I'm thinking of picking up a set of 04 wrx heads mated to a ej257 block with rs Intake manifold...

Any comments?

[kaos200]

its a few mm's of shaving, on each end of the manifold (to make it even) and the plastic piece must be shaved a few mm's as well. Its not bad, but you must take your time and do it right.

[Drac9]

So, a little off topic here, but I think you know the answer. I am putting some USDM Version 8 heads on my ej22t block. Will my MY99 Intake manifold work with these heads?

[kaos200]

If you mean USDM STi with AVCS, nope, no dice. The avcs hits the manifold...

[Drac9]

Damn, this is getting more and more expensive by the day. Anyone wanna buy a really nice, shiny, polished 99 manifold? What are my options without changing to new injectors?

[kaos200]

Id say screw the avcs heads, theyre not of much advantage unless avcs is working anyways.

[Migo]

bump...

I did the EJ257 with SOHC heads on a 2003 RS/TS. I bought turbo aftermarket coolant pipes but found it unnecessary, and it's a good thing I didn't spend time on lengthening the coolant temp sensor wires yet, because these were strangely not necessary for swapping the EJ257 on the 2003 RS/TS.

I did hammer the extra breather tube to fit the crossover coolant pipe, and siliconed it shut.

Grinding parts wasn't applicable on this...

I'm assuming that this FAQ is for the older 2.5RS?

[kaos200]

Originally Posted by Migo

bump...

I did the EJ257 with SOHC heads on a 2003 RS/TS. I bought turbo aftermarket coolant pipes but found it unnecessary, and it's a good thing I didn't spend time on lengthening the coolant temp sensor wires yet, because these were strangely not necessary for swapping the EJ257 on the 2003 RS/TS.

I did hammer the extra breather tube to fit the crossover coolant pipe, and siliconed it shut.

Grinding parts wasn't applicable on this...

I'm assuming that this FAQ is for the older 2.5RS?

Yes the notes were for the original GC RS's
If anyone would like to note the significant differences in any years after and let me know I'd be glad to modify the original post to reflect the changes.
Kian



edit: Once I get around to it I need to post up the chart I made for wiring in swaps.
Basically a pin by pin/ wire by wire how to for the popular model years.
So much stuff to do... So little time

[DZnutz]

Originally Posted by Migo

I did hammer the extra breather tube to fit the crossover coolant pipe, and siliconed it shut.

is this a good idea? id assume the breather is there for a reason. possibilty of building up unnecessary pressure by capping it off?

[White 2.5rs]

This is always in debate.
A lot of air flows through it, thats my input.

[kaos200]

Originally Posted by DZnutz

is this a good idea? id assume the breather is there for a reason. possibilty of building up unnecessary pressure by capping it off?

I'm definitely against that, it is there for a reason and blocking off that passage can't be good for anything. There are people that have done it, but I'm not sure of the outcome.

[turboed22]

I capped it. I was getting a ton of oil through it into my re-circ system
I am using a 22t though

[4S-TURBO]

i may just go down that yellow brick road afterall...

newb question: will a turbo x-member still be necessary to run the sti shortblock because of the oil pan/headers? i'm not too interested in grinding the stock one. thanks.

[Migo]

Originally Posted by DZnutz

is this a good idea? id assume the breather is there for a reason. possibilty of building up unnecessary pressure by capping it off?

A few other people actually pull the entire tube out, and weld the hole shut. I'm assuming that it is there for perhaps the extra stress/flow that the STi has compared to the RS, so I wouldn't pick 'yes' or 'no' because my application with my EJ257 is higher compression non-turbo....

But before I siliconed it shut, I had oil spewing everywhere out of that breather. The whole block was covered in oil and the oil was burning off under the hood, creating a large cloud of smoke. Other cars beside me looked quite nervous.

Originally Posted by 4S-TURBO

newb question: will a turbo x-member still be necessary to run the sti shortblock because of the oil pan/headers? i'm not too interested in grinding the stock one. thanks.

No there's no need for a turbo crossmember unless you want to eventually use turbo exhaust components. I reused my old oil pan and headers. Using a turbo crossmember is mainly for clearing an uppipe.

[4S-TURBO]

Originally Posted by Migo

No there's no need for a turbo crossmember unless you want to eventually use turbo exhaust components. I reused my old oil pan and headers. Using a turbo crossmember is mainly for clearing an uppipe.

which leads me to my next question: is the n/a oil pan sufficient to run, say, a bolt-on turbo kit that's designed for n/a x-member/headers, pushing a bar of boost with the sti s/b and n/a sohc everything else?

thanks migo!

[kaos200]

Originally Posted by 4S-TURBO

which leads me to my next question: is the n/a oil pan sufficient to run, say, a bolt-on turbo kit that's designed for n/a x-member/headers, pushing a bar of boost with the sti s/b and n/a sohc everything else?

thanks migo!

It's fine. Depending on what year your model is you may already have a regular wrx (5qt) oil pan, the older RS's came with 4.5 qt pans. The STis pans are different for twin scroll manifold piping (which... they don't even come with...)

[dogtranny 2.5rs]

sorry if this is a easy question but with the EJ257

would the DOHC or the SOHC be faster wen only naturally-aspirated

i just got a job and looking for a 1999-2000 2.5rs coupe

new to the forum too thanx