Small Block & Big Block Chevy Specific - 4.3L Mercruiser upgrades

Hey guys I'm sure some of you think this should be posted on a boat forum but those sites all suck.... So I've got a 19'.5" bowrider with a 4.3L non balance shaft with roller lifters v6 rated at 195 HP it cam stock with a 2 barrell quadrajunk & a stupid heavy cast iron intake... I was thinking about putting some 96+ 4.3L vortec heads a mild cam, 4barrell intake & 600cfm electric choke carb. Do you think it is worth doing the heads, or should I just do the cam , 4 barrell intake & 600 cfm carb?

Depends on what kind of boat you have.

You can add a ton HP to a boat engine but if the haul is not made to go any faster it will not help. So yeah it could be huge waste of money.

dont forget to look into different props too

Didn't forget about the prop, but I wanted to add more HP then a prop! :devil: keep em coming.

all the boat sites suck, haha you ain't kidding. i just troll iboats now to piss people off and find humor in their "marine" engineering rationale.
had a friend with around a 19', no bigger than 22', forget the make but was an open bow/bowrider with a 4.3L engine and merc alpha drive. I know he put a 4v carb on it along with an intake swap because he initially had a 2v carb. Don't remember if he swapped heads too, and I'm pretty sure he didn't do cam, the boat would run around 50-55mph, he gained a significant amount of speed over the previous setup but the thing was a dog getting on plane if there was any weight in the boat. when he pulled me on my slalom ski I sucked down half the river for about 30 seconds before the boat planed. I'm not familiar with the specifics of the 4.3L and the differences between the old heads vs the vortec heads for that engine, but I would bet the vortec heads would be most worth it. At minimum you'll be going to a 4v carb, which requires an intake change so at that point you should make it cost effective and get the vortec style intake, along with the vortec heads. And if you go that route, don't know what you prefer to run for octane but if you can mill the head and up compression ratio in addition that'll help a great deal. Do those 3 first, see how it is, then consider swapping out cams if they're available. The props won't give you much unless you're current is f'd up or way out of range for the boat. the best you'll do is a stainless 3-blade, I happen to like the turbo props by precision propeller, see soderbloom.com.

all the boat sites suck, haha you ain't kidding. i just troll iboats now to piss people off and find humor in their "marine" engineering rationale.
had a friend with around a 19', no bigger than 22', forget the make but was an open bow/bowrider with a 4.3L engine and merc alpha drive. I know he put a 4v carb on it along with an intake swap because he initially had a 2v carb. Don't remember if he swapped heads too, and I'm pretty sure he didn't do cam, the boat would run around 50-55mph, he gained a significant amount of speed over the previous setup but the thing was a dog getting on plane if there was any weight in the boat. when he pulled me on my slalom ski I sucked down half the river for about 30 seconds before the boat planed. I'm not familiar with the specifics of the 4.3L and the differences between the old heads vs the vortec heads for that engine, but I would bet the vortec heads would be most worth it. At minimum you'll be going to a 4v carb, which requires an intake change so at that point you should make it cost effective and get the vortec style intake, along with the vortec heads. And if you go that route, don't know what you prefer to run for octane but if you can mill the head and up compression ratio in addition that'll help a great deal. Do those 3 first, see how it is, then consider swapping out cams if they're available. The props won't give you much unless you're current is f'd up or way out of range for the boat. the best you'll do is a stainless 3-blade, I happen to like the turbo props by precision propeller, see soderbloom.com.

Sounds very similar to my boat set up with the alpha outdrive. I'm thinking that Vortec heads, intake & carb might be good since I can rev that 4.3L past 4800RPM because it only has 2 main oil gallies in the block, so a cam might be pointless. But 50-55mpg is impressive! I hope to get that.

Leave the stock cam in it. I would use the late model vortec heads and the 600cfm marine carb and four barrel intake. Cams are tricky in the boating field.

I know nothing about boats but if are still looking for some 4.3 vortec heads I have a pair that I had on my 01 s10 that i would like to sell they have been ported an polished standered size valves with some heavy springs that are rated for 600 lift im pretty sure, sitting in my basment collecting we had a procharger on the truck and made 425 at the tires on boost give or take 500hp flywheel let me know