hi i have a 05 rs and was wondering if you could swap the dohc heads and change heads with my sohc. IS THIS TRUE? ive been asking a many people and im gettin MANY different answers- YES or NO which is making me only more confused and angry. PLEASE ANYONE? WHICH IS CORRECT/ :mad:

Uh, enlighten me as to why you would want to do this?

so i dont have to do the complete engine swap to get a 2.0l wrx engine

so i dont have to do the complete engine swap to get a 2.0l wrx engine

:giggle:

Hmm, interesting... a 2.0l RS...

Back to the original question though, from what I understand, replacing the whole longblock is considerably easier. A little more information would be helpful, like why exactly do you want to change the heads?

YES, you can swap heads.

NO, its not a 2.0L wrx engine after you've swapped heads.

After you've swapped heads you still need the 2.0L shortblock, intake manifold, throttle body and a whole bunch of crap!

RS pistons are around 10:1 compression, where as WRX pistons are closer to 8.0-8.5:1 compression.

Exactly what are you trying to accomplish? Because a 2.0L WRX engine is crap without a turbo or anything. Would you like a Turbo car or a Naturally Asparated car? How much power do you want? How much money can/will you spend? Do you want to keep your stock clutch/tranny?

Nick

Subaru needs a high revving 2.0L Boxer N/A with 35+mpg. And a 6 speed, and Recaros and good suspension all for about 24k.

Subaru needs a high revving 2.0L Boxer N/A with 35+mpg. And a 6 speed, and Recaros and good suspension all for about 24k.
they have one, 2.0R with avcs, DOHC, I dont know about mpg, but they are over 200hp. Of course we dont get it :mad:

YES, you can swap heads.

NO, its not a 2.0L wrx engine after you've swapped heads.

After you've swapped heads you still need the 2.0L shortblock, intake manifold, throttle body and a whole bunch of crap!

RS pistons are around 10:1 compression, where as WRX pistons are closer to 8.0-8.5:1 compression.

Exactly what are you trying to accomplish? Because a 2.0L WRX engine is crap without a turbo or anything. Would you like a Turbo car or a Naturally Asparated car? How much power do you want? How much money can/will you spend? Do you want to keep your stock clutch/tranny?

Nick


whoever said anythin about swapping the ENGINE. i want to keep the engine, just make it dohc like the 06 imprezas. i plan on using my friends wrx stock turbo because he bought a new one.

On most engines this would be a good idea but from everything I have tried and heard it would be pointless!

Oh,
Don't we all wish it was this simple. There are several reasons why this just won't fly.
#1 DOHC WRX heads flow less than SOHC Ej25 heads. So, in that respect, there's nothing to be gained
#2 DOHC WRX heads have a smaller combustion chamber than SOHC Ej25 heads. If you bolt these to you block, your compression will go up, not down. I give this engine 30 days before it detonates to death...
#3 You can't just bolt a turbo to this. You need the complete turbo plumbing from intake through the intercooler, as well as the headers,up-pipe and down pipe. And this also requires changing to a turbo crossmember
#4 What are you going to do for engine management

Your best bet would be just holding out till you come accross a smashed Subaru with what U want and swap it over. ( long block-ECU-intake-exhaust parts ) Like a turbo Legacy-Baja-ect It will be a faster swap in the long run.....less headach less figuring out all the little details you will need, to go from scratch, and when ur done Your Done! You wont have to tune like crazy and keep after it like all get out

98 2.5rs is dohc, swap one of those in?

he wants a turbo...

98 2.5rs is dohc, swap one of those in?

if i were to swap a 98 rs wouldnt it be safe to put a turbo on it with all its accessories.

Oh,
Don't we all wish it was this simple. There are several reasons why this just won't fly.
#1 DOHC WRX heads flow less than SOHC Ej25 heads. So, in that respect, there's nothing to be gained
#2 DOHC WRX heads have a smaller combustion chamber than SOHC Ej25 heads. If you bolt these to you block, your compression will go up, not down. I give this engine 30 days before it detonates to death...
#3 You can't just bolt a turbo to this. You need the complete turbo plumbing from intake through the intercooler, as well as the headers,up-pipe and down pipe. And this also requires changing to a turbo crossmember
#4 What are you going to do for engine management

why would the engine blow up? i can always get a stronger block- was thinkin sti block for about a grand.

Um cuz the compresion will be so high if U where to put on WRX heads.

2.5rs block with stock pistons 11.0/1 compression. With a WRX head setup ( I think 8.1/1 compression on WRX ) compression will go up to I dont know....probly more than 12-12.5/1. Anyway you will bust a piston rod, or valve, blow a valve seal, all kinds of fun stuff could -will happen. That equals more $ to fix when you could prevent it from happening

If you rilly want to do it sweet and original steup go with a STi block and get your stock 2.5rs heads redone with like a Cobbtuning port-n-valve job. You will get better folw on the RS head than WRX and the valve job takes you up to like 7800rpm redline

Um cuz the compresion will be so high if U where to put on WRX heads.

2.5rs block with stock pistons 11.0/1 compression. With a WRX head setup ( I think 8.1/1 compression on WRX ) compression will go up to I dont know....probly more than 12-12.5/1. Anyway you will bust a piston rod, or valve, blow a valve seal, all kinds of fun stuff could -will happen. That equals more $ to fix when you could prevent it from happening

If you rilly want to do it sweet and original steup go with a STi block and get your stock 2.5rs heads redone with like a Cobbtuning port-n-valve job. You will get better folw on the RS head than WRX and the valve job takes you up to like 7800rpm redline

yeah man that is what i was planning. so if i got the block and had the rs head redone there wouldnt be a problem if i got it tuned right?

so why spend the same money and time to hybrid somthing crappy, when you could buy something complete and good?

most people on this forum know from experiance that its the best and cheapest way to go. you could easily find yourself a smashed WRX or STi car, throw all the wiring in your RS and have a proper WRX. im not going to harass you and tell you to dump the RS and just buy a wrx.......

so why spend the same money and time to hybrid somthing crappy, when you could buy something complete and good?

most people on this forum know from experiance that its the best and cheapest way to go. you could easily find yourself a smashed WRX or STi car, throw all the wiring in your RS and have a proper WRX. im not going to harass you and tell you to dump the RS and just buy a wrx.......

Moose, for once I am going to have to tell you that you are talking out your arse. Hybrid something crappy? :rolleyes:

Hmm, let's see... If the Ej25 SOHC heads are so crappy, why did the Rigolis dump the V8 STi heads to use them on their 8 second drag cars? Or look at Xyphyr's car. For the last few years he ran DOHC heads on his '98 RS hybrid with an STi Ej257 bottom end. That set up was putting out 408whp. That is uncorrected, at 5000ft. That would be pushing 500whp at sea level. last month he put a set of Cobb stage III SOHC heads on the car. He picked up over 40whp.

And, as I said previously, either of the types of Ej25 NA heads outflow WRX heads, in stock form. I personally wouldn't even bother with getting them Pnp'd. But telling him to get a WRX swap is going backwards. 2.0l displacment and lesser heads. And a complete Ej257 swap will run close to $8000 to pull off.

And before you jump in with your JDM is best garbage, let me remind you that the DOHC Ej25 heads are essentially EJ20K heads, so components of that quality and performance are readily available stateside.

The only real key to making this set up work is to get the Ej257 turbo shortblock and go from there. You can do this for $4000-5000 if you are smart. And you will see 300-350whp out of it...

neh.

noob+crazy hybrid + wiring nightmare = kaboom.

ej25sohc heads = good, why bother switch if do hybrid motorsetup? if i he has the guts to do it, keep the sohc and add 257 block + turbo kit.

think u got my line wrong-

damn. I just wanted to stir you up. Didn't work...

You should go the other way around instead of swapping heads - swap the short block with STi block, you get something like 8.5:1, and get some EM when you turbo. Don't bother swapping just the heads - it's far more trouble than its worth

one thing you should think about is, your car is DOHC, if you use SOHC heads, you need the ecu and wiring to go along with the SOHC heads, thats why lots of people put EJ25 DOHC heads on a WRX block, you get less compression, but you can run higher boost and use the current wiring. the same rule applies ofr going the other way with it too, SOHC car, DOHC heads etc., etc.


~Josh~

Um cuz the compresion will be so high if U where to put on WRX heads.

2.5rs block with stock pistons 11.0/1 compression. With a WRX head setup ( I think 8.1/1 compression on WRX ) compression will go up to I dont know....probly more than 12-12.5/1. Anyway you will bust a piston rod, or valve, blow a valve seal, all kinds of fun stuff could -will happen. That equals more $ to fix when you could prevent it from happening

If you rilly want to do it sweet and original steup go with a STi block and get your stock 2.5rs heads redone with like a Cobbtuning port-n-valve job. You will get better folw on the RS head than WRX and the valve job takes you up to like 7800rpm redline
Just seeing if any one else caught this and I will gladly eat it if I am wrong:

The valve job isnt what will let you rev to 7800rpm. You will need new valve train, springs buckets, shims. and a new ecu because your stock rev limiter are going to stop it way before then.

That is the valve job from Cobb.....that would be why its like $3000-$4000. When I say "valve job" I mean the whole shabang, to just replace one or two things in the valve assembly would be prety pointless. Perhaps I should have said Cobb stage II-III head/valve job

You can get your stock ECU reflashed to reset the RPM limit or get rid of it all togather ....I would not recomend the latter

http://cobbtuning.com/impreza/enginehead2.html#stage2

http://cobbtuning.com/impreza/enginehead3.html#stage3

dangerousatom,
I am going to take a shot in the dark and say that you have no personal experience with this? The reality is that for a turbo application, the only thing you need to change in a set of SOHC Ej25 heads is the valvesprings. And even that is optional if you are going to boost less than 20psi and keep it at 7500rpm or below. Spending a cent on Cobb heads is a waste of your hard earned money for anyone making less than 400whp. And unless you are using a gianormous turbo, you aren't going to making squat for boost above 7000rpm. When we start talking those kinds of numbers, we are talking about a $10,000 build and then maybe head work is justified.

Furthermore, there is not a reflash available to turn an NA car boosted. He must use a piggyback or a standalone.

Ballitch,
Actually, he already has SOHC heads in his car unless they went back to DOHC in '05 and I somehow missed it...

sorry for not making my thoughts clearer, and with a lack of specifics. I was following my thoughts of the whole swap over, STi block w/ECU or WRX ECU....for I thought U could reflash those ECU's with the ability to change the RPM limiter. Least that was what I was told would work for what I had planed on doin to my car.

Actually,
In that respect it is totally workable. Using a WRX ECU will give you all the tuning you need. I will be doing that on a car sometime next year. My primary motivation for it is that I live in an area with OBD-II plug in testing. I want my monster to be completely street legal in all 50 states...

thanks