383 MAG Inboard 4V

340 Crankshaft Horsepower

383 MAG Inboard 4V

There is finally the perfect engine to replace a 5.7L or 7.4L classic inboard. This engine delivers more torque than any standard 7.4L big block, and it does so while weighing 150 pounds less. Standard and opposite rotation versions are available, so you don't have to re-engineer your classic boat with a different type of transmission to make it go again.

  • Full roller valvetrain reduces friction and saves on fuel
  • 1-year factory backed limited warranty Available when purchased through any Mercury/MerCruiser authorized dealer
  • Up to 2 years of Mercury Product Protection available



Part Number Standard (LH) Rotation Part Number 8M0061212 - Transmission not included

Opposite (RH) Rotation Part Number 8M0061213 - Transmission not included
Horsepower @ flywheel 340
Kilowatts @ flywheel 254
Maximum RPM (WOT) 4600-5000
Cylinders Remanufactured GM V8 Marine Iron Block & Gen+ Heads - 062 Casting
Displacement (CID/L) 383 / 6.3
Bore & Stroke (in/mm) 4.03 x 3.75in
102 x 95mm
Compression Ratio 9.0:1 with Hypereutectic Pistons
Fuel Requirement 87 octane (R+M)/2
Engine Control System Thunderbolt V w/Knock Control - MIE Calibration
Fuel Delivery System 4V carburetor and mechanical fuel pump
Fuel Injection System / Carburetor Type 750 cfm Weber 4V with electric choke
Induction System Dual Plane Aluminum Intake Manifold with Bronze Inserts
Charging alternator amp 65
Charging alternator watt 917
Water drain system Multi-point drain - Hand Removable Blue Drain Plugs
Exhaust System Iron manifold with Dry-Joint Exhaust Elbow
Cooling System Thermostatically Controlled Raw Water - 143F
Accessory Drive System Serpentine belt
Lubrication System High Flow 100 psi Oil Pump and Copper Oil Cooler
Recommended Oil SAE 25-40 NMMA Certified FC-W Synthetic Blend
Rocker Arms 1.6:1 Full Roller Aluminum
Length (in/mm) 43in / 1092mm
Width (in/mm) 29in / 737mm
Height (in/mm) 22in / 559mm
Weight (lbs/kg) 980lbs / 444kg - When Installed with 72C Transmission
Features & Related Products Audio Warning System:
- Oil Pressure
- Coolant Temperature
- Transmission Temperature

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