jester1614

iTrader: (13)

my cousin has an 18 foot fiberglass boat and were assembling a 350 for it, its a 79 block stock cam currently, I was wondering what cams work good out on the water.

ZONES89RS

iTrader: (25)

I have no idea, but the more important part to worry about is the valve train, that thing will be going through extended high RPMs and i would worry about valve float and spring failure, so dont cheap out on any of those parts and if you can, make sure the oil return passages are in great shape, allot of people pert them and smooth everything out so that oil can return as fast as possible, higher RPMs for extended periods of time will really find the weak link in a engine.

jester1614

iTrader: (13)

yeah i have a few sets of springs that are all options for the car, as well as roller rockers.

1 FMF

iTrader: (1)

most stock merc cams are in the 198 to 202 duration realm. Going up to around 210 is usually no problem, if you're goal is all out speed then up around 220 duration @ 0.050" is about the most while still having < 900 rpm idle to be able to shift the outdrive and considering wet exhaust backpressure. If you have thru-hull exhaust that's above the water line then that helps but if exhaust goes through the outdrive and exits underwater then that'll prevent you from going with durations near 220, and you'll also want higher lobe separation angles (that'll depend on the duration cam you choose which will limit the size of the cam) to increase low rpm vacuum and help with idle. I think edelbrock or comp cams has a handful of cam choices listed by performance vs idle sacrifice.
you'll also need to consider rocker ratio, or what ratio you want. 1.6 is the performance norm, if you choose something more than that then definitely have the valvetrain to support high rpm use like was said. And all this is assuming you have vortec or similar 64cc heads giving > 9:1 compression ratio. If you're running the old heads on that 79 block then you're pretty much stuck with a small cam, a larger cam will not work on low compression. hopefully you're building that 350 with good heads and new pistons resulting in higher compression?

jester1614

iTrader: (13)

well it still has the stock heads, but I was also gonna ask about using a set of my lt1 (gen 2) pistons on either the lt1 rods or the stock 350 rods, I know that compression ratio will have to be figured out with the CC of the heads and such. also the rockers are 1.5 and or 1.55 ratio depending on what brand i am gonna give him.

what vortec heads are compatible with this block?

i will have to find out about the exhaust and such

1997bird

iTrader: (2)

Has the block been zero decked? The stock 882/993 casting heads that I have cc'd have measured from 76cc to 79cc in the combustion chambers untouched. Even with a flat top piston your compression will be low without decking the engine block and a Fel-pro replacement head gasket, about 7.23:1-7.04:1 with real engine math on a 4.00" bore 350. You would be better off staying with the stock cam but haveing the correct valve spring used and have the springs installed .050"-.080" of coil bind after max lift. I would use the higher ratio rocker arms to help the lift out.

jester1614

iTrader: (13)

what about using a set of gen 2 lt1 heads (modified of course) on the 350 block with the stock pistons and a carbed intake for the lt1 heads? i wanna say the gen 2 heads are 56-58cc

1997bird

iTrader: (2)

Are you going to have the block zero decked? It would be money well spent IMO. But yes it would help bring your compression up to 10.76:1 with it at 58cc head, zero decked, Felpro #1003 performance head gasket for the aluminum heads. Without decking the block it will be around 10.12:1 depending on how far in the hole the piston sits (most GM 350's have been from .022"-.037" in the hole). I figured 10.12:1 at .025" in the hole and I still believe that you will want to keep the quench tight for less detonation in the running engine. At 0.061"-0.076" quench you will be more easily prone to detonation with the low octane fuel we end up getting these days. You will want to keep the quench in the 0.040"-0.050" range and have less detonation issue's even with the elevated compression ratio from it.

96lt4c4

iTrader: (5)

Back when I had my boat, 19 ft Glasstron 305 Merc with a factory roller block, I put a stock LT4 cam in mine, ported the heads, changed springs and ran a set of Summitt 1.6 roller rockers. The little boat would scream, I could run 5500 RPM at about 55 mph easy. With just me in the boat and about 1/2 tank of gas I could almost hit 60 mph. Thats with the factroy 2 barrel Rochestor carb and me port matching the intake to the heads.

You need to watch the overlap of your cam on a boat motor, because your exhaust is mixed with water and if you have to much valve overlap you can suck water back into the engine threw the exhaust

If your block was a roller block I would say run the LT4 Hot Cam. It has just the right amount of overlap for a boat motor and sounds good out on the water. I knew a few guys with this cam in thier boat and really liked it.

For a 350 boat motor you cant go wrong with the Vortec heads. The stockers are junk. My 305 had the best heads that came on the 305, they were the same heads that were on the TPI Camaro motor 041's I think was the casting number. I even machined them for screw in studs.