Considering this cam for my twin 4.3 maxum 30ft - https://www.compcams.com/magnum-206-...2-4-3l-v6.html

SKU56-410-8, 206/206 260HR grind- shd make some noticeable difference in torque over the stock which tends to start tapering off around high 3000's which is kinda cruise territory imo- with some mild porting and deshrouding i think the vortec heads will produce excellent power gains as well in a large rig.

I played around with the edelbrock cam (not for balance engines but similar size) and it shows around 40 ft lbs increase on two 4.3s.. thats 20% over stock and the torque curve sits right in the 1200-4500 range..

Might even consider a regrind..

You have to consider that if you have more power and torque higher in the rev range, you will either need to raise your wide open throttle rpm or go up in prop pitch in order to utilize it. If you go up in prop pitch, then your boat will be more prone to struggle coming out of the hole. The fact that shifting the torque curve higher in the range means that you simultaneously lose torque lower in the range.

In order to maintain similar torque coming onto plane AND extending your power higher in the rev range, you will need to increase compression along with your cam swap. Increasing compression makes it more important to maintain a tight squish in your combustion chamber to keep swirl action high.

Let's say that your mods yield you 40 ft lbs of additional torque at 4500 rpm. This is easily enough to go up in prop pitch.

So you should do an experiment to see how well your boat will accelerate on plane with the higher pitch props. Borrow a set of props 2" higher pitch. Make sure your boat is full of fuel, as well as enough weight to duplicate a full crew, coolers, gear, etc.

Make a few pulls from 1400 rpm to 3500, and make a few pulls gently up onto plane and decide if you are still pleased with your ability to accelerate with authority.

If you ARE still happy with the low speed performance then you can proceed with your plans.
If the increase in prop pitch turns your boat into a dog that struggles to drag itself up on plane, then a cam swap might not be the right choice.

add a merc 525sc blower to your engines.

Well I posted the dyno graph to show the gains around cruise rpm 3400 to 3800.. very little shift in rpms if any . My props are not readily available and they perform excellent. Maybe a bump in static comp wd help but perhaps not mych.much.. for bigger cams yes but not sure it wd make that much diff since the cam is small.

Option 2 is snipers. They are incredibly good.. perhaps snipes and 260 cams..

I do build hot rod motors so familiar with the tech.. I'm keeping the max torque curve below 4200 .. this is a big boat so torque is king.

I've seen various specs on the cam specs can anyone confirm? Some are tiny 191 to 198 or there about.. other 205 ish which is getting into stage 1 territory..

Mine are the late model non adjustable roller vortec motors.. My thought are having more torque might reduce running rpms by 200 to 300 possibly and save some gas.

I'm spinning 4blade stainless big cow props on a b2. They are huge and equate to 20p 3 blade at least.. perhaps 21p.
Move alotof water or boat depending how u look atit.

They are on the edge as I can reach about 4300 wot and iirc about 32mph maybe 34 if super flat..

More torque wd reduce pitch imo.. in this case. Notlike im going for stage 2 or 218 duration territory .. the peak torque on the 260 is smack bang on the money ito rpm range.

I had a small boat in the early 90's that had a 4.3. We used it a lot for pulling skiers, tubing, knee boarding and such. It had a 2 bbl carb on it and I believe it was rated at 165hp. I don't remember the specs now, but I changed the cam, intake and installed a 4 bbl carb. At the time there were no aftermarket intakes available for the 4.3. I had to search for a factory 4 barrel intake that I believe was made and used for 1 year only on pickup trucks. It helped the boat in every way, more torque to pull skiers and also picked up speed up top. I do remember that I didn't change props. I am almost sure it was a 21P 3 blade.

I don't follow you when you say that more torque (from the engine?) equals less prop pitch.

A boat is not like a car.
Power (Hp) = Torque (ft x lbs) x RPM /5252
If you have ONE hotrod cammed motor and ONE stock motor in your twin engine boat and keep the same props, then at 26 mph and the engines synchronized to spin the same rpm, then both engines at that instant will be outputting the exact same torque. One may have the throttle opened or closed more than the other engine - but by definition they will both gave identical output.

But aside from that, I'm not understanding your goal. Is it higher top speed? Stronger acceleration? Better fuel economy?

And what goal is associated with the sniper EFI? Do you want it to start easier after sitting fir a week? Because a sniper can deliver that.

But unless your existing carburetors or factory fuel injection is in need of tune/tweak or out if calibration, AT CRUISE your engines are going to be able to deliver similar fuel usage regardless of what is spraying the fuel in it.

And again, with same props and same cruise speed, a sniper setup is going to be within half a hair of the same fuel burn as whatever you're using now (assuming it's working properly).

Now, cam and sniper and exhaust upgrades can increase the output of your motor, but if using same props, at the same cruise speed your boat requires the same hp to maintain that speed - period.

I'm interested in helping, but I dont seecwhere youre going.

I had a '93 206 Rinker that had the 4.3LX which was a 4 bbl. (Weber). Believe they rated it at 180 HP. Ran a 19" Mirage Plus.