DIY Converting Chevy Engine for Marine Use

by Kyle McBride
itstillruns article image
Jupiterimages/ Images

Chevrolet engines can be converted for marine use with a few simple modifications. Gasoline engines can provide strong, reliable power for boat propulsion. Parts are easy to get from auto parts dealers and can be much lower in price than marine-specific parts from a marine supply business.


Install a cam with a broad power-band from 500 to 5000 RPM (revolutions per minute), ideally. Engines that are built for road use have a very narrow power-band. The transmission allows the operator to keep the RPMs in the usable range and adjust speed with the gears in the transmission. Marine transmissions have only one speed forward and one speed in reverse, leaving no way to increase speed without a proportional increase in engine RPMs. The torque generated by the engine will fall off rapidly once the power-band range is exceeded. Replacing the cam with a broad power-band type will allow the engine to deliver power as soon as the throttle opens and continue all the way through the maximum RPM.

Flame Arrestors

Install a flame arrestor on the carburetor. Gas fumes are heavier than air and can fill an engine compartment. Any ignition source can cause it to detonate. The flame arrestor will prevent any flame caused by backfiring from igniting the collected gas fumes.


Use an ignition-free alternator. All alternators create sparks inside as they operate. Ignition-free alternators have screens that dissipate the heat and prevent the outside of the alternator from reaching ignition temperatures. Ensure that any other switches, pumps or devices in the engine compartment are ignition-free.


Cool the engine with a keel-cooler. The keel-cooler is a closed circuit system that will allow you to run antifreeze in your engine, instead of circulating raw water. The antifreeze circulates through the cooler and transfers heat to the outside water without introducing saltwater into the engine. Auto engines are not built to stand circulating saltwater and they will very quickly deteriorate with raw water cooling.

Use non-ethylene glycol based antifreeze in your keel-cooler. Ethylene glycol forms a jelly like substance when it comes into contact with saltwater. This jelly will clog the water passages in the engine block and head and can cause the engine to overheat and inflict severe internal damage.

More Articles

article divider