Is it a lake boat or ocean boat? Is it open or closed cooling? If you run in the ocean and it's open cooling then you could convert to a closed cooling system. 2 major benefits, the engine will make more power if you can control the temperature with a thermostat and the life of the engine will be extended by keeping that salt water out of the engines. This is a big benefit also if you decide to go with aluminum heads! I have carbed 502s with heads, closed cooling, intakes, and cam upgrades making 565hp!

Jim

You are correct. When starting from scratch and using aftermarket parts, the cost is about the same. A 4" and 4.25" crank are about the same money. The rods and pistons are the same as well. There is no reason that a 540-565 short block should be more than a 502 short block, assuming the have the same quality parts. Obviously, a 540 with an aftermarket crank, rods and pistons will cost more than a stock 502 with GM parts.
Eddie

600 from a 502 with some tweaks? What if it is carbed? Can that still be done and what torque numbers are we talking?
Thanks!

I have a intake and carb off a stock HP500 for sale. I think its a dart intake and a 800 holley. $500 call me if your interested
765-210-1124

I went through this process several years ago with 502 efi. I spent way too much money prior to going inside the engine only to pick up a few mph. Try to make sure that you are adding parts that you can use when you decide to go to a 540.

600HP from a carbed 502 is just as easy, if not easier, than making it with a Merc EFI. The 500EFI manifold limits the power that can be made to around 600hp. You don't have that restriction on a carbed engine.

Your heads and cam are the restrictions to horsepower.

A Crane 731 or stock HP500 cam is pretty trouble free and will give you around 450HP with a jetting tweak on your carb.

Bigger cams than that, with untouched stock heads, will give you more power, but at the cost of idle quality and spring and lifter life. Those cams with a good set of heads will get you over 500 horses.

Great heads and efficient cam is always the route that makes for a happy boater.

GOOD heads, and a custom cam will deliver all around performance, maintain idle quality.

Intake and carb that you have is good for 520 horses before you hit the wall. Above that, the right intake and bigger carb make things easier.