The EJ25 Engine is in fact a SOHC, 16 valve engine... but due to the boxer design (damn proud to own one) the SOHC really refers to the single overhead cam that is located on each head. In a sence, it is a dual, SOHC The EJ20 is a DOHC, or in a sence, a dual, DOHC ( 4 cams!)

Now, as for the difference between the RS and the WRX. Reguardless of what anyone tells you, buy the WRX. Period. $5000 will not even get your RS close to the WRX in performance, and I dont even care if you bolt on a super or turbo... the whole RS drive train is built to reguarly handle about 200HP maximum. After that, things start breaking. I am speaking from experience!

I had a 2000 RS. Loved it. Did just about every bolt on mod short of a light weight or underdrive pully. I was pushing about, oh, 195 engine HP. Ill tell you, the damn clutch would slip sometimes. Whats worse? The factory fuel cut off is at about 6300 rpms. About 1000 lower than the WRX.

Lets just put it this way. My new unmodded 2003 WRX anihlated my old modded RS. Now, about only $1800 dollars later, and Im pushing about 285 engine HP. Unfreakingbelievable. And, btw, wait until february to buy a WRX. I got mine for $22300 new

There is no replacement for displacement... except forced induction