Two 4.6-litre V8s, both pushing 300 horsepower. On paper, the Mercury Racing 300R and the brand-new 300 ROS are close relatives – but on the water, they speak entirely different languages. One is a versatile high-performance outboard for offshore-minded boaters, the other is a factory-built race weapon. If you run fast cats or deep-vee centre consoles in New Zealand or Australia, the 300R is the proven Mercury choice for serious speed and control. If your weekends involve race courses, rules, and chequered flags – and you’ve got the class approval – the 300 ROS might be your new obsession.
From launch ramp to race dock
Mercury Racing released the 300R in May 2018, replacing the two-stroke 300XS. It arrived with a naturally aspirated 4.6-litre DOHC V8, a 5,800–6,400 rpm operating range, and the flexibility to run on 91-octane fuel (in New Zealand). Gearcase options included Torque Master and Sport Master, with a choice of mechanical or Digital Throttle & Shift controls.
Last week (7 August 2025), Mercury Racing unveiled the updated 300R and introduced the 300 ROS – short for Racing Outboard System. Built for competition, the 300 ROS shares the 300R’s powerhead but adds factory above-water exhaust, a racing trim cylinder, and the 5.4-inch Sport Master gearcase.
Both the 300R and 300ROS have the new game-changing 15-inch Heavy-Duty Conventional Midsection (HD CMS). The new 15-inch Heavy Duty Competition MidSection (HD CMS) is engineered to deliver sharper handling, reduced flex, and improved stability at speed. It’s built to handle the punishment of high-speed turns and the repeated load changes that come with racing.
The HD CMS features heavy-duty solid mounts, a reinforced swivel bracket, and a robust clamp bracket assembly. The result? A noticeably tighter feel in the helm, especially when cornering hard in choppy water.
The boatie’s weapon: Mercury 300R
For performance-minded boaters, the 300R strikes a rare balance between speed and civility. It’s equally happy on a fishing cat, a multi-engine game boat, or a ski-day runabout.
Under the cowl, a short-runner intake manifold and high-lift cams deliver rapid throttle response. Through-prop exhaust keeps things quiet at idle and under way, while the 85-amp alternator handles the demands of electronics, pumps, and lights.
The 300R packs a 4.6-litre V8, with a short-runner intake manifold and high-lift intake camshaft that team up for sharp, punchy acceleration.
The 300R has long been Mercury Racing’s flagship for high-performance recreational boating — think high-speed centre consoles, performance cats, and luxury sport runabouts. Until now, it ran a standard midsection, which, while quick, wasn’t optimised for heavy competition-style loading.
The introduction of the 15-inch HD CMS changes that. The 300R now benefits from race-grade stability and responsiveness, making it an even more tempting option for recreational boaters who want sharper cornering and better control at speed. For New Zealand’s growing performance boating scene, this upgrade could be a game-changer, especially in rough coastal conditions.
Enter the 300 ROS
The 300 ROS is unapologetically single-minded. Built for closed-course domination, it’s for sanctioned racing, with hardware built for punishment. It uses the same base platform but comes with racing-specific calibration, lightweight rigging, and the same 15-inch HD CMS as standard.
- Above-water exhaust – quicker breathing, more noise, easier service.
- Racing trim cylinder – instant bow attitude changes.
- Sport Master gearcase – low-water pick-ups and surfacing propellers.
- 15-inch HD CMS – forged brackets, solid mounts, and that lower centre of gravity for stability at pace.
This gives racers the same midsection stiffness and control benefits as the refreshed 300R, but with tuning aimed at maximum acceleration, sustained wide-open throttle, and race-class reliability.
Mercury Racing’s Jeff Broman explained the thinking: “We’ve incorporated upgraded components designed to best withstand the rigors of offshore racing… giving both competition and high-performance recreational boats extreme durability and the handling benefits of a lower center of gravity.”
READ ABOUT TRAVIS PASTRANA MAXES OUT NEWEST 300R AND 300 ROS OUTBOARDS
Clear intentions
Mercury Racing’s integration of the HD CMS into both the 300R and 300 ROS shows a clear push to bring competition technology into the hands of both serious racers and hard-charging recreational boaters. In Kiwi waters — where offshore racing and fast coastal runs are part of the culture — that’s welcome news.
