Well its cold as hell, a plan for a 502 should fill some time and be fun... and help me figure out what to do. So the motor has a manufactured for GM tag on the side part # 12568778, it has heads with casting #12562934 and brass freeze out plugs. I dont know if its a marine or not. Their is a set of tube style headers that are dry to the tip.

Price point of say $6000. Durability takes trump over performance. I would like to get around 500 hours out of the top end if that's possible. With that said I would like to get as much performance as possible also.

If this is what you are buying, it shoud be a good base for a marine engine build.502 HO Tech Specs

• Part Number: 12568778
• Engine Type: Chevy Big-Block V-8
• Displacement (cu. in.): 502
• Bore x Stroke (in.): 4.470 x 4.000
• Block (P/N 19170540): Cast-iron with four-bolt main caps
• Crankshaft (P/N 10183723): Forged steel
• Connecting Rods (P/N 19170198): Forged steel, shot peened
• Pistons (P/N 12533507): Forged aluminum
• Camshaft Type (P/N 24502611): Hydraulic roller
• Camshaft Lift (in.): .510 intake / .540 exhaust
• Camshaft Duration (@.050 in.): 211° intake / 230° exhaust
• Cylinder Heads (P/N 12562920): Iron rectangular port; 118-cc chambers
• Valve Size (in.): 2.190 intake / 1.880 exhaust
• Compression Ratio: 8.75:1
• Rocker Arms (P/N 12523976): Stamped steel
• Rocker Arm Ratio: 1.7:1
• Water Pump (P/N 19168606): Cast-iron, long-style
• Flexplate (P/N 10185034): 14"
• Recommended Fuel: Regular Pump
• Ignition Timing: 32° Total @ 4,000 rpm
• Maximum Recommended rpm: 5500
• Balanced: External

The motor is what I already have with the headers. I dont know weather to just freshen the motor up (probably the smart thing) or try to get as much power as possible with some new heads and/or cam (what will prob end up happening because i never stick to my plan of doing things cheap or easy. lol )

Speed Calculator
This is a good place to estimate your max speed using weight, hull efficiency and HP. The one thing that will lose weight the quickest will be your wallet.

No way you will get 500hrs out of valve springs with any decent sized cam.
With what you have now and your budget, swap out the cam for a Crane 168731.
Cam, lifters, roller rockers, springs, etc will run about 2k + valve job and some head work for prob around 1k.
It would be a very close build to an HP500.

Bottom end cost will depend a lot on what is needed.

I like your style! If the man was going to disassemble to freshen up, would it be worth decking the block to bring up the compression?

Jeff

What is a reasonable time frame for springs?

What is a reasonable time frame for springs? I know it is dependent on cam lift to an extent, but with what I have I cant go to radical anyway.

200-250 hrs ^^^^^^^^^

I think you will want at least 500 hp in that boat? 90 percent of the time it's plenty on the lake... On the bay,more would be nice. Those damn jet skis are fast these days and it sucks when they creep by ya. Lol