Tom Your 100% right! it ain't rocket science,but good machine work is a must!

Per Hot Boat article of three years ago or so, the "webbing" of the block ( at the bottom of the piston skirts) is heavier/thicker on the merc block that that GM crate 502s. Also, the cam in a crate 502 / 502 is reported to have "reversion" problems/risks if run without "dry"headers.

MAV (Just another guy that reads the mag - articles)

Maverick you dont really think that GM has two different cstings for automotive and marine blocks do you? I think hot Boat is Yankin ya....

I wonder what Merc really thinks now that GM is in APBA.

Dyno

I have engines built off of the crate Gen 5 502. The valve train, valves and intake are different than GM but other than that bone stock. Un-ported iron squareport heads and make 600 horse and are as reliable as a 330. My machine guy is in Troy and he is the difference. Ask Kamma about Jomar he is only a couple hours from you and worth the trip.

GM had one cast for the 502 block. There is no differance between a marine and a street bare block. Of course the cam, valve train and ignition timing will be different. A street motor has a more broad torque curve than a marine application ,say any where from 850 rpms through 3500 4000 with a normal driving rpm range of 1200 to 2500. A marine motor doesnt really need any torque untill after about 2500 or 3000. Think about this example, drive your car around and see where the tach reads most of the time, then when your in your boat see where the tach reads. I know in my boat the tachs very seldom read under 3000, unless I am idling. So really the differance between a marine tuned motor and a street motor is in the cam and the ignition curve in the distributer. Any question let me know.

Don

Used 502 blocks $500
ph # 504 279 2460
Unless there cracked or complete junk ya cant beat that. Build a short block all new with good stuff and machined for 2k or less

Dan

WOW Dan you the Man!!! anyone know where the 504 area code is?

504 is the New Orleans area of LA. The guys name is Ron Sprol. He's located in a town just south of N.O. called Chalmette. He runs an ad in Powerboat and Hotboat every month that has prices. He has a large inventory of used parts an is great to deal with. I have bought several parts from him in the past and he was always straight up. He buys the engines Merc replaces under warranty I think. He builds race motors for teams across North America including Canada. He has a large super clean air conditioned machine shop. Call him he can probably set you up with whatever you need. You can buy a block and crank and have him do the machine work. He sells parts, shortblocks, longblocks, and complete engines.

Ron

What year??
Mark IV / Gen 5 / Gen 6????????????

The big question is - "How Used are they"