I've done quite a bit of research on marine 383s but haven't dropped the hammer on one. There are some nice pieces out there from big name builders, but they are prohibitively expensive. Also a lot of $2000 ebay specials that I wouldn't trust in a boat for more than a season. Probably do great in a car that sees 5k rpm once or twice a month, but not nearly robust enough for marine use. There's surely a sweet spot somewhere in the middle, but I can't tell you exactly what that is; one of the remanned Merc 383s from Michigan Motorz is probably pretty close.
My inclination is to build one myself so I know what's in it and know who to blame if it craps the bed. A really robust, bullet-proof bottom end would provide a lot of confidence when you drop the hammer. Good new blocks are not much more than a used block after machine work, so I would start with a fresh block (probably Dart). Summit and others also have prepped 383 blocks for less than you could get it done yourself. Scat 383 kits are supposed to be better than the Eagle stuff, and I think the forged is worth the extra cost for this application. Forged crank / pistons / rods, plus bearings & rings is just over a grand - God bless the small block Chevy.
Stock Vortec heads with screw-in studs and beehive springs will support 400hp, but my preference would be some AFR 195s or other aftermarket aluminum heads, particularly with closed cooling. Getting away from the 64cc Vortec heads also opens up way more options for pistons without going over a 9.5CR. Call Bob Madera at Marine Kinetics for a custom hydraulic roller cam based on the rest of the build, or for out of the box Comp and others have some great cams in the 270 duration range. Rest of the valvetrain based on whatever the cam manufacturer recommends. Stainless intake and inconel exhaust valves would be a plus. Marine head gaskets for sure, and good ARP hardware.
No idea on your EFI supporting 400hp, but there are very few folks that can tune the stock MEFI box. I like EFI, but from a practicality and cost standpoint I'd throw a 750cfm carb on there and call it good. Edelbrock RPM Air-Gap is a good intake, as are the regular RPM and a lot of other high-rise dual-planes.
Exhaust - probably GLM aluminum manifolds and some SS risers.
Ignition - stock TBIV or V.
Tin - big ass 7+qt oil pan with a windage tray. Valve covers are tough on the SBC to find something that will fit with roller rockers and still clear your exhaust (especially center-bolt). Pretty sure you can hog out the oil baffles in the stockers and clear everything.
Doing it yourself the right way is a $5k+ proposition depending on how much of your current setup you can reuse, but it would be a reliable 400hp and pretty darn satisfying. I would rather go that route and have a premium motor vs. one of the online specials that I would never personally trust. Or find a local builder and work closely with him to get what you want; he may be able to source the parts a little cheaper as well.
If you find the holy grail of stout marine 383s in your hunt please let me know!
Last edited by duckhunter; 12-24-2013 at 02:33 PM.
Reason: atrocious grammar
"Speed's fine, but accuracy is final."
- Bill Jordan
1998 Donzi 21LXR
1971 Boston Whaler 13