The MerCruiser 7.4-liter MPI (7.4L MPI), is an boat engine manufactured by Mercury Marine, a American company headquartered in Fond du Lac, Wisconsin. The 7.4L MPI is an inboard motor which, when attached to a sterndrive unit, propels the vessel through the water.
The MerCruiser 7.4L MPI is a gasoline powered, fuel injected, 8-cylinder, 4-cycle marine engine. It delivers 310 horsepower (HP) to the propeller shaft at a maximum of 4,200 to 4,600 RPM at WOT (revolutions per minute at wide open throttle). It is a large engine with 454 cubic inches (7.4 liters) of displacement.
The 7.4L MPI comes standard with a 72-amp alternator that charges the 12-volt, negative ground electrical system. The recommended battery rating is a minimum of 650 CCA (cold cranking amps) with 150 Ah (amps per hour).
For purposes of a tune up, the correct timing setting is 8 degrees BTDC (before top dead center) at idle of 600 RPM. The firing order of the cylinders is 1-8-4-3-6-5-7-2. Oil pressure is 30-70 PSI (pounds per square inch) at 2,000 RPM and 4 PSI at idle. Normal operating temperature of the 7.4L MPI is 160 degrees Fahrenheit and is controlled by a thermostat.
- Zubin Shroff/Digital Vision/Getty Images