Ok total noobie here when it comes to "marine" engines.

I am looking at upgrading the rotating assembly, heads, cam, and probably the fuel system.
My question is where do you guys buy your cranks, rods, pistons, bearings etc

I've looked at raylar engineering but i think i can put together a kit much cheaper.

is there a difference between the forged pistons for the 8.1 truck engine vs the 8.1 marine engine?

I was told at one point the main difference in marine engines vs automotive engines was the bearing tolerances hence the different viscosity of oil required.

Finally, after i install everything what business can i send my computer to have them load a tune on it?

Thanks in advance.

Mercury sourced GM 8.1 longblocks for the 496 platform and marineized from there. No special bearing clearances, etc.... Same longblock as if you bought a 2500HD truck with the 8.1.

The stock GM crank is good to 650ish HP. Very nice piece for stock. Wiseco forged pistons. Use a 6.7" H beam rod with a .990" pin. Clevite makes performance bearings dedicated to the 8.1.

Go with Larry's heads and cam setup from Raylar. Their 315 CNC heads are really nice pieces.

If your keeping the 555pcm, then Whipple can custom tune and has base map tunes for Raylar setups.

502 replacement the way to go. the 496 parts are going away. Some of the parts I am going have made. One system part assembly I have the proto type as we speak.

Anyways just saying -- One can easily build 550 to 600 hp from a 502 right out of a jegs catalog.

Tyler Crockett built some really nice 580 hp 496's for a boat I looked at recently. Cam, valves, springs, exhaust, rods, pistons, intake, and tune is what he did.

I completely forgot about him. I will have to swing by his shop and see what he can do for me.

His shop is 10 minutes from my house lol