Freshwater cooling, not saltwater, I hope... You'll still want to use brass 'freeze plugs', not steel...
Yes, you can try porting the exhaust side of your heads, but the marine manifolds will negate most of your gains.
Your OMC engine probably already has a torque-grind cam, but I'm sure that can be improved upon with a more modern grind to maximize your engine torque at 2500-3600rpm and still have a nice smooth idle to keep your marina-mates happy.. You also might want to bump up the compression a bit to ~9.0-9.25:1 if you can...


Copied from another 460 boat post:

I'd message or call Paul Kane on here. He's a big Ford boat guy.

Paul Kane

www.460ford.com

 

Thank you.
I'll message Paul.

Engine is raw water cooled but I'm in fresh water on lake Simcoe in Ontario so may not be a big deal.

marine manifolds will negate most of your gains.

Is this why some people switch to dry exhaust?

I'm sure that can be improved upon with a
more modern grind to maximize your engine torque at 2500-3600rpm

Can you recommend a good supplier of such cams so I can talk to them?

 

Just perspective on how to approach this, IMO, as I have done exactly this in order to increase my own small V8 prop from 15x12 to 15x14, and similar for others. While your build can be generally tweaked into the most beneficial operating range, your ultimate results will be based on tuning of the package to achieve highest efficiencies for both peak power and peak economy.

For a combined target like that, I prefer to tune sharply to everything it can give now, which will clearly show where and how much it's lacking to hit or exceed targets without extra cost and work in areas it is not required. Better is better anywhere, but you want specifically better, and is a way to focus on that. This should provide a clear vision and allow a clear plan for what is specifically needed.

I would suggest borrowing a good tuning kit for the Holley, and the Progression ignition (or similar) will help substantially to quicken and ease the process to best results. You are fortunate to have a boat, which is equivalent to a steady-state dyno. Use it effectively. A couple hours for a first-time effort should have plenty of good answers for you.

 

I would suggest borrowing a good tuning kit for the Holley, and the Progression ignition
(or similar) will help substantially to quicken and ease the process to best results.

Unfortunately, my boating season is over, and I'm looking for recommendations on the internal components upgrade during this winter to give me the best possible, or at least a better base for fine-tuning next spring.

Should I stick with OEM components as much as possible and replace only what's broken or in poor condition with the same part, or are there better, newer options? ...as long as I have the engine out of the boat and am replacing things.

While the cost is always an important consideration, I'm not looking for the most budget-friendly solution (which would be "not buying a boat" )

 

There's an old adage about boats being a 'hole-in-the-water that you throw money into'... It could be worse - I also fly airplanes!!!!

 

 

I don't know the torque curve of the cam you have now, with your combination of parts. Perhaps someone here or on a Merc site does. A dyno graph is easiest to see that curve and where peak under the curve is. That would tell you if a cam change would be beneficial.

In a general sense; for a combination of economy cruise plus equal or better top-end, you want a cam that peaks higher with max area under the torque curve between 3200 and 3700 rpm. Peak torque translates to peak volumetric efficiency (and why peak is there), which should provide peak economy efficiency in that range, and with better power to handle more pitch.

I upped my cruiser's power about 12% and a cam to one that peaked in-range, and raised top-end by about 300 rpm even with the higher pitch. With that pitch, full-throttle from rest (hole shot) would then harshly cavitate the prop. Rolling into it, or ±2/3 throttle until getting close to plane would move fine, then wide-open. It would only hit 4200 until speed increased on-plane, then climb to 45-4600. 😁 Just be aware, hole-shots may be weird if it's used for skiing (especially if loaded heavy) unless the driver knows to stage or roll the throttle. Not predicting yours, but just an example of possible unexpected changes with mods like this.

 

I don't do skiers, this is just a simple cruiser which becomes a raiser as soon as another power boat is moving in the same direction - just a few minutes to see who is willing to burn more $ on stupidity.

you want a cam that peaks higher with max area under the torque curve between 3200 and 3700 rpm.

Where would I find a provider of such cams?

 

I see @The Mad Porter was recommended on this forum for custom cams. I'll contact him about this.