http://www.thehulltruth.com/boating-...-outdrive.html
From Baypro
"I went from a old, tired 235hp 5.7 4 barrel to a 300hp and gained 8mph at 3400rpm's after repropping. I don't think a supercharger is your only option. I believe you will see a noticeable differance with:
vortec heads // hi-rise aluminum intake (marine) // and a cam with these specs: lobe lift intake .287 exhaust .300 // duration intake .307 exhaust .294 // this gives a valve lift of .431 in and .450 ex. with 1.5 to 1 rockers (your cam may already be within these specs).
I believe the better breathing vortec heads makes most of the differance but you need a intake with them (differant bolt pattern). The al. intake manifold should be good for 10-15hp.
I was cruising at 3400/24mph and now cruise at 3275/30mph. My best cruise economy went from 2.25mpg to 3.4mpg.
The alpha drive handles up to 300hp, I avoid full throttle accelleration (not needed anymore anyway) and I very rarely use wot."