Neighbor has a pair of stock 330-340 inboards out of his sea ray both standard rotation.Bought a offshore boat with no engines .Wants to use these,>reason for removing them was one had a blown head gasket and he re-powered with fuel injected engines.Now he is removing the heads and was asking if a head and intake manifold change would give him a little more HP.Does not want to get into the lower end.Has small ovel port heads on it now.Just want a little more than 340 HP Just a river boat .Wants to use the engines because they were well taken care of and are closed cooling system .Any thoughts or help would be helpful. Thanks JOHN SR

454;s merc 420 and 525sc used standard cheap rect port heads. next limiting factor, cast crank, little rods 4600 rev limiter tons and tons of info out there,

the crank will hold 450 ish hp but the rods are only 3/8 with the tiny rod rod bolts..like mentioned heads and cam but i would use air gap intakes..more user friendly..

grab rectangle ports, dual plane intake, and cam for 46-4700 rpm, should be fine... bottom ends are not the strongest but I dont see the power being enough to worry about anything.

Full Force How about large ovel ports? Just any type square port.Thanks JOHN SR

Ihave seen good success with aluminum oval ports, not sure what budget is, I was thinking cheap budget, Gellner was offering a nice Brodix head already set up for Marine with Inconel, maybe give him a call see if hes still doing it...Dean told me when I was looking at doing my 454, now I went to 540 so thats out the window...

https://www.google.com/url?sa=t&rct=...79908130,d.cGU

Hmm, I thought I'd replied but I guess it did'nt show up.

Mysuggestion is to change to Dart Iron Eagle heads, roller cam, Dart intake and Holley 750. Yoiu will make 450+ hp cheap and relable.

Wannabe

ttt

Ttt? There's a few good suggestions here. Anything else is going to be contradictory and get confusing

Gm 781 ovals make good power. I had a 330 bottom end. Used 781 ovals, edelbrock performer, comp extreme marine flat tappet, 830 holley, scorpion roller rockers, and imco powerflow exhaust. Made a solid 450hp at 5000 and it ran awesome for years until I overheated it not realizing my tilt switch wasn't working running in shallow water.