making this for all the newbs
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).
is good to atleast 7500rpm (from personal experience, others may go higher, im not that crazy)
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.