Specs for an HP500 Engine

by Richard Manfredi

The Mercruiser HP500 EFI sterndrive engine package was first introduced by Mercury Racing in 1999. A sterndrive motor provides propulsion to powerboats through a two-part system, with the power-producing shaft drive on the upper half of the unit inside the boat and the propeller outside the boat on the lower half. As of November 2010 the Mercruiser HP500 EFI has been replaced by the Mercruiser HP525 EFI.


The eight-valve Mercruiser HP500 EFI sterndrive produces 470 horsepower (hp) or 390 kilowatts (kW) of power, with a maximum of 5,200 revolutions per minute (RPM). It features a precision CNC-machined cast iron cylinder block with a displacement--otherwise known as size--of 8.2 liters or 502 cubic inches. The engine has a maximum alternator output rating of 60 amps and alternator wattage of 847. It has also received a three-star CARB rating from the California Air Resources Board, meaning it meets the agency's 2008 exhaust emission standards and produces 65 percent fewer emissions than one-star rated motors.


The HP500 EFI from Mercruiser weighs 1,113 pounds and is 39 inches long, 34 inches wide and 22 inches tall. It has a bore and stroke of 4.47 inches by four inches, along with a multiport fuel injection system featuring a high-flow throttle body to increase horsepower and a tuned intake manifold to provide a better fuel/air mixture. The engine runs on gasoline rated at 87 octane or higher.


The standard drive unit on a Mercruiser HP500 EFI sterndrive is a Bravo One XZ with either a right or left-hand rotation--which turns the propeller clockwise and counter-clockwise, allowing for improved speed and handling. It has a gear ratio of 1.36:1 or 1.5:1, allowing for faster or slower cycling through gears. Additional drive options available are the Bravo One XR, Bravo One XR Sport Master, Bravo One Short Sport Master and Dry-Sump Six. Bravo One XZ and Bravo One XR drives include separate dual-water pickup and low-water pickup gearcase housings.


The connecting rods on the Mercruiser HP500 EFI sterndrive are forged from fully machined and 4340 alloy steel that has been shot-peened through a cold-working process to reduce stress. It has a hydraulic roller camshaft, providing increased torque at lower RPM speeds, which reduces fuel usage and increases performance. The large oil cooler is thermostatically-controlled to quickly raise the oil engine temperature to optimal operating levels and keep the oil temperature within a consistent range. The oil thermostat and positive crankcase ventilation valve are designed to reduce oil condensation, which can lead to thick buildup of viscous fluids inside the engine block. The serpentine belt system is a one-piece unit that requires less power to turn the engine parts and helps increase potential hp.

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