What are the simple differences between engines?

Pratical use of automobile engines in boats ? what are the differences for rust, corrosion protection?

• I'm always dreaming up wild ideas, and I had one for a new breed of high performance personal watercraft - the Tube boat. I want to put a V-8 engine into a very stretched Seadoo-type watercraft, and just use a simple propeller shaft off the back of the engine, with maybe a simple clutch mechanism to engage/disengage the power to the shaft. Anyway, that all said, I know boats use automobile-type engines, but use special water-cooled exhaust manifolds, etc. What other Boaterizing is done to an automobile engine to make it into a "marine" engine? Any special gimmicks to prevent the corrosion of dissimilar metals inside the motor? If I chose to use a straight car engine, with the watercooled boat manifolds, how long would a motor last without any other mods? Obviously a boat style cooling system as well would be installed <duh>. So other than radiator, coolant, and exhaust manifolds, what else would normally be changed?

• Answer:

  A marine sticker and a large increase in the price. although there are specialized marine engines that use special alloys to prevent corrosion (ie atomic 4, westerbreke diesels) most of your cheaper ski boats use a car motor core for economic reasons (ie cannot put a $10,000 marine engine into a brand new Bayliner that retails brand new for $8995) As for your question of how long one will last, depends on the water quality ran through it, salt, sand, silt, algae all change the lifespan. Most boats die of neglect than anything else. Although you can use an air cooled radiator in a boat,(seen it done) its easier to use the water underneath it. I would suggest a heat exchanger, that way you can add antifreeze rust inhibitors to the water going through the motor. Boats either use a dry exhaust or a wet exhaust. Dry exhaust is like a car, no water going through the exhaust manifold. The exhaust pipe is hot, there is usually vented above the boat instead of through the hull. They are usually used on racing style boats (ie drag boats with striaght pipes are common) A wet exhaust, water cools the exhaust manifold, and is usually sprayed into the exhaust a couple inches from exhaust manifold. This allows used of a rubber hose to vent the exhaust through the hull. Coast guard requires a flash arrestor on carburator engines, a piece of window screen will meet this requirement though. Nothing says you have to use a carb, fuel injection works just as well in a boat. As for you gearbox, (transmission) the typical propeller will caviate and loose effieciency long before a engine will redline. Usually a set gear ratio is used to match optimum prop rpm with optimum engine rpm . Most boat use a set pitch, set diameter prop, with either is good for top end or for acceleration. Variable pitch props are out there but are expensive. Also, marine engines do not run backward, on multiple engine boats the direction of props is changed in the gearbox.