I am going to be purchasing an Impreza in the next couple months. The dealer I talked to couldn't give me the info I wanted. I was hoping you all can help.
First, which imprezas have which engine? I know the 02-05 RS is a 2.5 SOHC, but what about before 02 or the new 06 RSi and WRX? There are a lot of 2.5's, but what mods will interchange? Which ones are DOHC or SOHC? I also have heard mention of an ej20 and ej25. What do these signify? Is there part of the VIN # that can help me out?
Finally, i plan on buying an RS and going crazy with mods (turbo, valves, head, etc.) over the next couple years (making my own WRX, but with a SOHC's torque curve :devil: ). Has onyone tried it yet and how would they compare?

Thanx fellas!!!

woah lots of questions. 98-present rs's have a 2.5 liter motor. only the 98 had a dohc motor, meaning 99+ all have sohc.

ej25 is the 2.5liter motor. ej20 is the 2.0liter turbo motor as found in the 02-05 wrx. 06 wrx has a 2.5liter turbo.

all mods (ie exhausts, pulleys, etc.) are interchangable on all 2.5 motors. intakes are too, but not all 2.5's used a maf sensor, but obviously there are different intakes available for different years. aftermarket internals are mostly interchangable, but if you are doing head work, obviously buy something that is made for dohc if you have it, or sohc if you end up with that. building an n/a rs isn't really worth it though. i've seen someone put about 10 grand into a 2.5 motor and only come out with about 250hp... i think the most someone has ever squeezed out was just shy of 300hp, and that was with EXTENSIVE work.

if you plan on buying an rs and turboing it, i'd suggest buying an older gc8 bodied impreza rs or L, (93-01) and doing a wrx motor swap in it. i've done it to mine and it screams (much lighter body and a much better transmission). i just blew my rex motor though and am now moving on to an sti motor.

you can turbo the 2.5liter motor in the rs, but after a while its not worth it. the blocks are very weak since the cylinder walls are so thin (all subaru motors are based on the same block, but just have different bore sizes, with 2.5 being the largest). also you will need engine management and to run low boost (around 6psi max) unless you go with lower compression pistons, and even then you're still limited to what the motor can handle. my suggestion would be to find an old impreza l (dirt cheap now) with a 1.8liter motor and boost that... those motors are built very strong and can make tremendous amounts of power if done right. from what i remember, they also have the best flowing heads. also know that all blocks and heads on subaru motors are interchangable. lots of guys who boost their rs's use the ej257 (sti block) which is designed for boost, along with their rs heads and intake manifold...

hope this helps.

-mike

I bought a 2.5i last week. I love it. I'd like to do some basic mods. Since I plan on getting a WRX or STI in '07 I plan to keep it simple, intake and exhaust, and suspension stuff.