I forgot to mention that marine engines use head gaskets made of corrosion resistant materials, too. Marine engines often (but not always) have forged components, especially the crank and rods.

Michael

That would be like shifting into high gear at 30mph and trying to go up a steep hill. A boat hull has a lot more resistance than 4 spinning wheels on a car.

paint it blue and put a mercury sticker on it and you will have magically turned it into a marine engine.

"Marine engines have an extra .001"-.003" bore clearance because of high load operation and cold water to the block. A cold block with hot pistons is what dictates the need for extra marine clearance."

http://racingsecrets.com/article_racing-10.html

People overlook this very important fact all the time. They are usually pushing a rope back to the dock!

I agree with all of the above. Since the early 1980's I have seen lots of boat guys who had a machine shop that is used to building great car engines fail when they were in stalled in an offshore boat. Piston to cylinder wall clearance, piston ring end gap, valve guide clearances all has something to do with "thermal expansion". The weight of oil you use and keeping it cool is important as well.

Finding a good precision machine shop that builds a truly decent marine engine is hard enough itself. Even many of these guys and their machine shops who are used to building great car engines for the past 20+ years....they have a lot of pride and you can't tell them anything because they think they know it all because of their sucesses with car/street engines. Think twice before you take your engine(s) to a machine shop used to building car engines...street, drag strip, oval......no matter how good they are. It is usually hard for them to grasp the marine offshore engine thing.

Also, cam differences. The only thing I could think of that would even be close to a marine cam would be a tame hi-perf street legal cam. You have to consider the engine's RPM operating range and the application when used for a marine engine.

The best way I have heard a marine engine being described is: A marine engine is like a semi pulling a full load of heavy cargo up a mountain. The torque has to be there and you have to keep everything cool at the same time.

Sorry about the soap box presentation. Have fun.

Can anyone (specifically anyone who works/worked for either company or has FIRST hand knowledge- not I know someone who knows someone) answer the question of what is the difference between the short block that GM performance sells -ZZ502 - and the shortblock that come with the "marine engines" from 1800runsnew and the likes. We are talking about only the shortblocks (not heads, cams, etc). You can buy a GM ZZ502 shortblock for approx $ 4400 I think and the 1800runsnew total engine is about $ 5400. Is someone taking apart these shortblocks, changing/checking clearances, balancing and reassembly, and then charge only an extra $1000 for the entire motor?? Point is I have heard that the 415 horse 502 comes from a plain GM performance shortblock (forged piston, steel crank, 7/16 rods etc.) and the 500 hp was disassembled and changed/checked, balanced and reassembed. Sorry for the long post.

Very interesting perspectives. I know for a fact the guy that machined my engine is very very very PROUD. He got Really , Really pissed off when I asked him if I should plasti gauge the bearing clearance's etc. He said no! Thats what you paid us for. ( I plasti gauged anyway ).Anyway, that said, It sounds like I would be better off not to put this engine in a boat, I know the crank and rods are not forged, I know the piston clearance and rod bearing, ring gap and etc is to manufacturer specs. My measurements showed the bearing clearances were on the tight side of the range and so were the ring gaps. I would assume those spec's are for automotive use. Sounds like I would be pushing my luck. I have no idea on the 502 question.

I don't think anybody asked what you were going to put this in. If it were going in a light weight 16 foot jet boat it would probably work fine with the right impellor. We are on OSO so I assume it is going in something bigger.

I have done some experimenting with this I bought new a boat with a 350 mag blew it up and tore it down I found no 4bolt main cast pistons and crank nothing different than a 78 chevy truck engine. I even ran my 350 mag cam in my 78 chevy truck to see what it would do and how it would react I found not much different than the cam it came stock with. I even tore apart the starters one from the truck and one that said marine stamped on it and found no difference they were exactly the same. The water pump on the front of the marine motor went bad had a gm pt# matched up to a 68 corvette. I built a marine small block without using marine parts but with marine clearances except for carb, fuel pump, and alt and ign and it has performed flawlessly for over 700hours. So go figure.