Mercury Racing 450R Outboard Review

A Boating expert opines on this new Mercury Racing outboard.

Mercury Racing turns up the volume on outboard performance with its new 450R model, a 4.6-liter V-8 with a ­supercharger system. This high-performance outboard supersedes, but will not ­replace, the popular Mercury Racing 400R model. Mercury Racing claims the 450R cranks out 450 prop-shaft horsepower and 439 foot-pounds of torque burning 89-octane fuel—40 percent more torque than the ­Mercury Racing 400R. Yet at 689 pounds, the 450R weighs just 21 pounds more than the six-cylinder 400R.

You’ll pay for that power. Pricing for the 450R ranges from $54,000 to $64,000, depending on gear case and other options—about 50 percent more than the Mercury Racing 400R. Availability of the 450R will be limited for the remainder of 2019, with production earmarked for performance boatbuilders, and few left for repower installations through dealers.

Mercury Marine 450R at top speed
Putting out gobs of torque—439 foot-pounds—that doesn’t quit makes the 450R ideal for big, fast boats plying often in rough, open water.Courtesy Mercury Marine

At a demo session organized by Mercury we had a chance to run the Mercury Racing 450R on a variety of boats from Formula, MTI, Nor-Tech, Mystic, Cigarette and Sea Ray, and to talk to reps from those brands who could compare the performance of the 450R to that of the 400R on the same boat model. All reported an increase in top speed, from 5 to 10 mph, and all raved about the snappy mid-range punch of the new motor.

Mercury Marine 450R outboard
Mercury Racing’s new 450R is an outboard powerhouse.Courtesy Mercury Marine

“The 400R starts out strong, but then seems to sort of run out of breath as you build up speed,” says Mike Griffiths, who was manning an MTI 340X cat. “The 450R’s torque starts early and stays linear. This motor pulls hard all the way to wide-open throttle.”

The 450R is based on the naturally ­aspirated Mercury Racing 300R outboard, which in turn has its foundation in the 4.6-liter double-overhead-cam, four-valve 64-degree V-8 platform used across four Mercury outboard series: Verado, FourStroke, Pro XS and Ocean Pro.

“This entire platform has been in development since 2013, and the Mercury Racing version of the 4.6-liter V-8 was always part of the program,” says Mercury Racing head engineer Jeff Broman. “Mercury certainly knows how to supercharge an outboard, so that aspect of the project was not a significant challenge. The toughest task was fitting our supercharged powerhead under the same slim-line cowl used for the normally ­aspirated versions of the V-8.”

Cutaway of the Mercury Racing 450R
This cutaway of the Mercury Racing 450R shows the twin-scroll supercharger placed on the front of the powerhead.Courtesy Mercury Marine

The 450R features forged pistons, a high-performance intake cam profile, and race-spec Inconel exhaust valves. A 2.4-liter belt-driven twin-screw supercharger is water-cooled to reduce the temperature of the intake air. Twin charge-air coolers reduce the temperature of the compressed intake charge. The supercharger and charge-air coolers occupy the space filled by the intake tract on the normally aspirated V-8s. A bypass valve automatically adjusts maximum boost pressure in response to changing ambient conditions. A high-capacity oil cooler and a poppet valve in the midsection provide an on-demand higher volume of cooling-water flow to help manage increased engine heat. Gear-case options include the Mercury Racing Sport Master for boats capable of speeds over 85 mph—now with a new one-piece 1.25-inch-diameter stainless-steel prop shaft—and the 5.44 HD for lower-speed and traditional submerged applications. Both gear cases have a 1.6-to-1 gear ratio. The ­wide-open-throttle operating range peaks at a generous 5,800 to 6,400 rpm, a broad window for propping options. The 450R will be offered in 20-, 25- and 30-inch shaft lengths.

Mercury Racing propeller
The Mercury Racing propeller options for the 450R outboard include the Max5 and Outboard CNC Cleaver, required for the Sport Master gear case. For the 5.44 HD gear case, the Mercury Racing Bravo I FS, Bravo I LT, Enertia ECO XP, and Rev 4 XP are available. Mercury Racing Pro and Lab props cost $1,600 to $6,000 and are hand-finished by a select crew of artisans who take a lot of pride in their precise work, and so, like any artist, each takes ownership by signing their work. You’ll find their initials stamped inside the prop barrel.Courtesy Mercury Marine

The 450R has the Verado-style Advanced MidSection (AMS) with stainless-steel guide plates and stiffened ­engine mounts for improved engine stability and ­high-speed handling. The AMS has an ­integral tie-bar mount, and enables optional Joystick ­Piloting for Outboards (JPO) for boats rigged with two to six outboards. Other features carried over from the base ­4.6-liter platform include a 115-amp alternator to handle big audio systems and power-hungry angling accessories, the Idle Charge battery-management system that bumps up idle rpm when it senses low battery voltage, and preprogrammed Transient Spark Technology that adjusts timing advance for stronger hole-shot performance. Adaptive Speed Control with a Mercury Racing calibration automatically holds engine rpm regardless of load or condition. The Top Cowl Service Door makes routine engine-oil checks a breeze.

It’s impressive that this high-performance outboard is backed by a three-year limited factory warranty and a three-year limited corrosion warranty —just like the plain old Mercs. Color options include Cold Fusion White with Devil Red Eye cowl accent panels and Phantom Black with Graphite Gray cowl accents. A carbon-fiber and paint-ready accessory accent panel kit will be available to custom-match a 450R outboard to a boat’s color scheme.