I am doing valve replacement on a 1997 dohc ej25 , and I'll have to do valve ajustments too. Really currious to know if the later hydraulic lifters and shorter valves can fit in these heads, It would be nice to just replace the valves, lap them in and put it back together. Ordering shims and waiting to put it together is a pain (every 105k or so).

No, the heads are completely different. Nothing from them interchanges.

or - install EJ22 heads instead of the EJ25 heads and use an EJ22 intake manifold and timing belt to match.

probably cheaper than replacing a bunch of valves and no more shim/adjusting madness.

Does that significantly affect comp ratios? intake velosities? Power? Fuel efficiency? Any other benifits besides the hydraulic adjusters?

there are hydraulic and standard screw type adjusters, you can get what you want.

 

compression ratio goes up a bit...i don't get into this for performance modifications so i won't comment on this in terms of performance, though in general it seems most folks like the results. and they'll likely comment in a bit.

 

no annoying valves, improves on the headgasket debacle, cheaper and simpler timing belt and maintenance - all around better. 

 

the EJ22 head bolts are external - so you can have a head off in no time, no removing valve covers, hard to access head bolts, etc.

Ej22e heads will bump your compression significantly, near 11:1. Research high compression frankenmotor for more information as to what you'll need to set one up. You'd need a complete donor ej22e to source everything you'd need for the conversion, there is the possibility of swapping on 96 ej25d heads as these are hla heads but that will drop your compression ratio to about 8.5:1 great if you want to turbo it but probably not the most economical option.