i had a 4k that was bored out to a 5k, completlely balanced, shot peened rods, 11.5:1 compression, lightened flywheel, ported head, 304 deg cam and a 32/36 webber as well as 2 1/2inc exhaust and extractors. it made 56 rwkw's and it revved to 8 (as far i felt safe to rev it).
if i were you i would either biy 1) an ex sprint motor, or 2) just get high comp pistons and do more headwork
you can drift 4k's properly. its fun, but as soon as i got an e7 with a 4age, you know what rolla's are really about.
although the 4k sounded f@$kin cool.
don't get an s13. major disrespect points.