2018 Mercury 300R - 25 in. Shaft

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300R - 25 in. Shaft



The 300R FourStroke is the highest performing engine in its class. The naturally aspirated 4.6L V-8 provides an astounding 44% in increased displacement and up to 40% higher overall bottom end torque than the legacy two-stroke 300XS it replaces. Custom Racing intake cam profiles and short intake manifold runners maximize power throughout the rated speed range. An integrated oil cooler keeps oil temps down throughout the Racing exclusive 5800-6400 rpm operating range.

Transient spark calibration boosts torque by 7% for unmatched acceleration. Advanced Range Optimization automatically adjusts fuel delivery for up to 10% improvement in cruise-speed fuel efficiency.

All of this on 87-octane (90 RON) pump fuel while maintaining a comparable weight as it’s legacy two-stroke cousin. Best of all, the 300R is backed by a three-year factory warranty.

  • Class Leading Performance: Naturally aspirated, 4.6 Liter V-8; 44% higher displacement than the 3.2L 300XS OptiMax while maintaining a comparable weight.
  • Reduced Operating Cost: 300 rated horsepower on readily available 87 octane (90 RON) pump fuel.
  • Unmatched Torque: Class-leading 4.6L displacement resulting in 40% more bottom-end torque.
  • Maximized Power: Racing exclusive intake cam profile and short intake manifold runners for maximized power throughout the rpm band.
  • Integrated Oil Cooler: An integrated oil cooler keeps oil temps down throughout the 300R’s higher 5800-6400 RPM operating range.
  • Exhilarating Acceleration: Transient spark calibration boosts mid-range torque by as much as 7% for superior acceleration.
  • Enhanced Efficiency: Advanced Range Optimization automatically adjusts fuel delivery for up to 10% improvement in cruise-speed fuel efficiency.
  • Versatile: Mechanical or Digital Throttle & Shift (DTS) control system options for enhanced repower versatility.
  • Idle Charge Management: Idle charge battery-management automatically increases engine idle rpm to boost alternator output as needed, ensuring batteries are always charged to the proper level.
  • Class-leading Battery Charging: High-capacity alternator produces 42% higher charging output vs. the legacy 300XS OptiMax.
  • Easy Maintenance: An industry-exclusive Top Cowl Service Door simplifies routine maintenance with easy oil checks and oil fills without removing the cowl. Graphic, hour-based maintenance decals under the cowl for easy access to all regular powerhead maintenance points.
  • Maintenance Free: Maintenance-free valve train for life of the engine.
  • Sports-Car-Like Drivability: Tri-Ram midsection with a stiffer, high-durometer elastomer upper mount and solid lower mounts for enhanced handling at higher speeds.
  • Race Proven Durability: Heavy duty midsection models come with solid mounts and an ultra robust, forged transom brackets with single ram power trim and remote trim pump designed to endure the harsh offshore environment.
  • Integrated Rear Tie-Bar: Factory rear tie-bar models are available for enhanced stability on high speed multiple engine catamaran and offshore center console applications. An optional side steering bracket kit is also available.
  • Sport Master Gearcase: The surface piercing Sport Master gearcase, designed for boats capable of speeds in excess of 85 mph, features low water pick-ups and a crescent leading-edge for maximized efficiency and speed.
  • Torque Master Gearcase: Dual water pickups enable the Torque Master gearcase to run partially surfaced. It carries the load of heavier tournament bass boats and multi-species hulls while maximizing top speed and drivability.
  • 5.44" HD: The 5.44? HD gearcase, featuring dual water pickups, is designed for use on bay boats and multi engine performance center consoles where the application requires a more submerged gearcase.
  • Hand Crafted Propellers: A full arsenal of custom Mercury Racing propellers are available to maximize performance in any application.
  • Color Options: An optional Graphite Grey accent panel is available as a kit. A paint-ready kit is also available to custom match the engine to the boat.
  • 3-year Limited Warranty: The 300R is backed by a factory three year limited warranty with up to two additional years of Mercury Protect Protection available.
  • Rated Horsepower (HP/kW): 300/224
  • Bore & Stroke (in./mm): 3.6 x 3.4/92 x 86
  • Idle RPM: 600
  • Max RPM at Full Throttle: 5800-6400
  • Cylinders/Engine Configuration: V-8 (64 degree) with 32-valve Dual Overhead Cam (DOHC)
  • Displacement (Liter/CID): 4.6/279
  • Induction System: Custom Racing Short-Runner Intake Manifold
  • Fuel System: Electronic Fuel Injection (EFI) Computer Controlled with Advanced Range Optimization
  • Fuel Requirements: Unleaded Regular 87 Octane Minimum (R+M/2) or 90 RON 10% Ethanol Maximum
  • Ignition System: SmartCraft PCM 112 Digital Inductive
  • Charging System: 85-amp (1071 Watt) with idle Charge
  • Starting: Electric Start with SmartStart Protection
  • Lubrication system: Integrated wet sump
  • Oil Requirement: NMMA Certified FCW SAE 10W-30
  • Throttle and Shift Controls: Mechanical and Digital Throttle and Shift (DTS)
  • Tri-Ram Midsection: High-Durometer Elastomer Upper Mount and Solid Lower Mounts
  • Heavy Duty Midsection: Solid Mounts; Remote Trim System
  • Gearcase: Torque Master, Sport Master or 5.44" HD
  • Gear Ratio: 1.75:1
  • Cambered Skeg: Sport Master and Torque Master
  • Gear Shift: F-N-R
  • Dry Weight (lbs./kg): XL - 25": 556/252
  • Warranty: 3-Year Warranty



Engine Type
V-8 (64 degree) with 32-valve Dual Overhead Cam (DOHC)
Bore x Stroke
3.6 x 3.4 in. (92 x 86 mm)
4.6 L (279 cid)
Electric Start with SmartStart Protection


Shaft Length
25 in.
556 lb. (252 kg)


Propshaft Horsepower
300 hp (224 kW)
Full Throttle Operating Range
5800-6400 rpm
Gear Ratio / Shift
1.75:1 / F-N-R
Fuel Induction
Custom Racing Short-Runner Intake Manifold
85-amp (1071 Watt) with idle Charge
3-Year Warranty


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