car engines verses marine engines

Depends on the engine. However most marine engines would be considered to be heavy duty use. The usual differences are the camshaft, crank is usually a forged item, the heads are usually heavy duty types. Intakes are usually designed a bit different with regard to cooling issues and the water pumps are high flow units.

Several dealers sell marine conversion equipment for auto engines. I once had a converted Chev 283, and the differences were these:

1. Water-cooled exhaust manifolds. The closed-in type of engine in a boat means no airflow around the exhaust and they would get red-hot and cause a fire hazard. The cooling is via jackets in the manifold, and the water leaving the engine is also dumped into the exhaust itself to cool it further and muffle it some. Only in wide-open installations do they use non-jacketed marine headers, but they're still cooled by the heated water leaving the engine, which, as with the jacketed system, is dumped into the exhaust manifold to cool the exhaust itself.
2. You might need an oil cooler and adapter to direct oil from the filter mount though the cooler and back to the filter. No airflow around the oil pan, see, and a hard-working engine that generates a lot of heat. The transmission, if it's a hydraulic type, will need another oil cooler.
3. A positive-displacement water pump that draws water from beneath the boat. The centrifugal pump found on auto engines won't lift the water unless the system is pre-primed, a real headache, and if the system gets a little air in it the prime is lost again and the engine burns up.
4. The thermostat housing is changed to one with a couple of 3/4" hose nipples, and the water pump cavity is closed off with a cover having a similar nipple. So the water is drawn from the lake, through the pump, through the oil coolers, divides and runs through both exhaust manifold jackets, out of those and into the water pump cover and through the engine, out the thermostat housing and into the exhaust manifolds where it's blown out with the exhaust.
5. If the engine is mounted at a radical angle as with a straight- shaft setup, the carb must be mounted on a shim to level it.
6. Engine mounts are rigid if a straight-shaft setup. The shaft is bolted rigidly to the transmission's output flange and the engine/ trans can't be allowed to move around.
7. A marine transmission, probably the most expensive proposition of the whole works. Most of them are forward/neutral/reverse, using clutch packs similar to those found in a car's automatic transmission. The thing is really stout, much stronger than an auto tranny.

Get ready to spend lots of money to do it right. See

You also need a prop shaft, prop, strut, stuffing box, and on and on.

But it's fun.

Dan