See full version: Why cant have car motor with rad in boat
For instance, I have a stock Melling Mercruiser grind for a 350 that specs out to 194/204 duration on a 114 LSA. Nothing fancy about it, just a normal stock grind. Worked great in my station wagon, but ran out of breath at 5000. more
Change the cam, add an intake and "big" carb, and instant "hot rod". (:-
My post was simply to outline the differences between a "marine" and other engines. I have no doubt, the marine BBC pulls hard in the car.
I'm an old man. 10-12 years IS "recent". (:- more
This motor is considered a "modified" motor and will make the boat fast with a low run time. High torque low RPM will give you realistic looking run, the 19 turn will make your cabin cruiser more like a hydroplane. Also remember that the lower the turns the lower the resistance in the motor which means higher the current draw. Some ESCs cannot handle the lower turn motors and will burn up. more
Yes, you can use car motors. We do it all the time. But be aware, a boat is a different animal and you can easily overheat and destroy your car spec motor. Consider this: a boat prop is always putting a load on the motor. Unlike a car, where it will reduce resistance once it is rolling. So a comparison might be like this: holding the tires still while trying to turn them over with the motor. Lots of resistance. That is what a boat is like. So you need to prop it "small" to start with, and work up to a larger prop if desired. All the while, checking motor, esc, and battery temps every minute or so until you are sure it is not overheating.
Good luck, and post pictures!
Can you use car motors? Yes. Just make sure that you have an ESC that can handle the motor and that the type of boat is good for the power of the motor you are using. Also you may need to get a water cooler for the motor. more
Multiple Gears
An automotive engine kicks down to a lower rpm at top speeds. In contrast, a marine engine's sustained speed only increases with sustained rpm. Basically, a truck motor has four to six gears, and a marine motor has one. It only makes matters worse when a boat engine isn't properly broken in. more
Here’s why a boat can’t achieve the fuel efficiency and longevity of the truck that tows it.
Today’s marine engines are high-tech wonders. Flush them and change the oil at regular intervals, and you should expect hundreds of hours of faithful service. Yet we still often hear casual boaters wondering why a boat can’t achieve the fuel efficiency and longevity of the truck that tows it, especially since they share the same engine block. Here’s why.
Frequency of Use
A car engine has an advantage in that it gets run every day, and engineers say hours are good. Think of it in terms of physics. Things in motion stay in motion. An object at rest tends to rust — from the inside out. more
Many boats have auxiliary generators. Again, most are diesel, but there are some manufacturers that make gasoline powered generators for boats. There is a difference between a marine generator and a generator not intended for use on a boat. The differences are the same as for auto engines and marine engines. Do not use a non-marine generator on your boat. See https://newboatbuilders.com/docs/portable.pdf [links]
Another subject that seems to puzzle people not familiar with marine engines is engine rotation. I am not talking prop rotation here, but the actual direction that the engine turns. The reason for the confusion is, on older marine engines, when you go shopping for parts they ask you, what is the engine rotation? The direction it rotates determines the part you get.
12. Cooling can be raw water or closed cooling. Raw water is picked up by a through hull routed through the engine and then dumped into the exhaust generally where the riser exits to the exhaust line. Closed cooling uses a radiator much like an auto but it is called a heat exchanger. more
More Thoughts on Marine Engines [links]
10. Carburetor: The carburetor on a car and on a boat may look the same but internally they are not. If the float sticks in the bowl and fuel flows out the vent on a car it goes out of the carburetor. On a marine carburetor it goes down the throat. Marine carburetors are not allowed to spill any fuel into the boat. Plus that, marine carburetors have different jets and setup because of the different duty cycle. They need to be tuned to run most efficiently at three quarters throttle, usually about 4500 rpm (the rpm varies depending on the engine). more
7. The head is usually heavier with larger water passages.
Can’t you make the parts? Possibly, but doubtful, or maybe yes and no. Motor mounts, cover plates, pump adapters and many other parts have and can be made. However, making marine exhaust manifolds is another story. A marine manifold jackets the exhaust chamber with water. Making and welding a manifold so each chamber is separate plus, fitting it to the block-bolting pattern is a formidable project. Many have tried but, in our experience, few have succeeded in making a useable manifold. here
Very early conversions simply amounted to lifting the motor with transmission from the car and slapping it in a boat. Several things were quickly learned. The exhaust manifolds became red hot and the circulating water pump didn’t adequately cool the motor as a radiator and rush of air through it was not used. Since the motor was set in at an angle, the carburetor would flood and the oil pickup in the pan would run dry. The transmission was never intended to absorb the forward and reverse thrust of the propeller, and the clutch and very low speed of the reverse made rapid braking impossible. These are but a few of the problems; most were quickly solved.
Be warned. If you get a chance to get a motor from Aunt Gertrude’s low mileage old car, pause for a moment. Be sure you can get the parts required to marinize it before congratulating yourself.
What about the transmission? Marine transmissions are readily available and, with an adapter plate, will fit to almost all automobile motors. What about using the auto automatic transmission in a boat? It can and has been done, but, with older transmissions and internal changes. Such a transmission will be considerably longer than a marine gear and it won’t take the forward and reverse thrust. Shifting from forward to reverse as a brake may create excessive wear on the auto transmission. Then, too, the unit probably reduces the rpm’s in reverse. It’s difficult to duplicate the marine gearbox by converting an automotive one unless you are particularly adept and very familiar with the inner workings of these units.
Converting an automobile motor to a viable marine engine has been going on for years. Although, going back in memory, many of these conversions were disasters waiting to happen.