Medusa 400

There is a new Sheriff in town. Our entry level engine, fittingly, more powerful than the top of the line Volvo Penta, Mercruiser and most others, and that about says it all. 435 horsepower and 470 ft-lbs torque of water churning power! And at only 500 lbs, compact enough to fit in small engine bays, leaving plenty of space for daily checkups and routine maintenance, which makes for long lasting engines.

The Medusa 400 is our most popular engine for good reason: it is the perfect replacement for the thousands of boat models between 1965 and 2005 that came originally equipped with gasoline engines up to 502 cubic inches, or even older diesels like the Detroit 53, 71 and 92 series.

But it goes well beyond a repower, as the Medusa 400 will achieve quicker acceleration, faster planing and better fuel consumption that any of those engines by a big margin. Breathing new life into most boats produced in a 40 year span makes the Medusa 400 the most versatile engine ever made!

Build Sheet

  • Block: GM. 4-bolt main, 1-piece rear main seal, cast iron.
  • Crankshaft: SCAT. 4340 forged stainless steel.
  • Connecting Rods: SCAT. 4340 forged stainless stell, I-beam
  • Pistons: PROBE. Forged aluminum, -22 cc dish, 9.1:1 CR
  • Camshaft: HOWARDS. Hydraulic roller, lift: int .500/ ext .510, duration @ 0.050": int .225/ ext .231, angle: 110 degrees.
  • Rockers: SCORPION. Full roller, 1.5 ratio, forged aluminum.
  • Cylinder Heads: NKB. Aluminum, 200 cc runners
  • Valves: BPM. Stainless Steel, 2.02" intake/1.60" exhaust.
  • Intake: PROFESSIONAL PRODUCTS. Aluminum, Crosswind, dual-plane.
  • Ignition: MSD. 8560 Marine Billet Distributor + 6M-2L control box/rev limiter
  • Carburetor: QUICK FUEL. Marine Series 600 CFM, vacuum secondaries and black diamond coating.
  • Fuel System: HOLLEY 110 GPH marine pump with fuel regulator, 10 micron fuel filter/water separator and AEROMOTIVE flexible steel fuel lines.
  • Exhaust System: MEDUSA. Stainless Steel headers inside stainless steel water jacket, raw and fresh water capable, integrated anode.
  • Cooling System: MEDUSA.  Fully closed, fresh water. 60 GPH crank mounted raw water pump, high flow heat exchanger & 3-year coolant.
  • Alternator: DELCO. Marine 120 AMP.
  • Starter: DELCO. Marine 1.6 kw, top mounted.


  • Type & Displacement:  DOV 90° V8, 383 cubic inches/6.3 liters, 4" bore x 3.75" stroke.
  • Power Output: 435 HP @ 5500 RPM, 462 ft-lbs @ 4100 RPM
  • Compression Ratio, Idle & Max RPM: 9.1 : 1 CR, 800 RPM idle, 5000 max RPM (rev limited)

Target vessels: