An all-new 4.6-liter V-8 powerhead is the next step in a complete re-vamp of the Mercury Marine high-power outboard lines. With a rating of 200 to 300 HP, the double overhead-cam, four-stroke V-8 will be deployed across four Mercury outboard series: Verado, FourStroke, Pro XS and Ocean Pro. It will replace the 2.6-liter supercharged four-stroke L6 Verado models through 300 HP and the 3.0-liter OptiMax Pro XS models from 200 to 250 HP. A high-performance version of the 4.6-liter V-8 will also be offered by Mercury Racing.

Note that the supercharged 2.6-liter L6 Mercury Verado 350 and the Mercury Racing Verado 400R models will remain in production.

Mercury has not yet released pricing information for the V-8 models, which are in production.

Cowl-off shot of new Mercury 4.6-liter V-8 shows top-mounted dipstick and oil fill, long intake runners from an single throttle body, and sound-damping covers over the fuel injectors.

Paired with the February introduction of the 3.4-liter V-6 FourStroke models, the launch of the 4.6-liter V-8 represents the culmination of a product paradigm shift at Mercury Marine. The new V-6 and V-8 powerheads follow a design philosophy established in in 2011 with the introduction of the 3.0-liter, four-cylinder Mercury 150 FourStroke model – generous displacement to produce reliable, stress-free power and a focus on user-friendly design that makes the motor easy to maintain and easy to rig for new-boat or re-power applications. The same ideas were applied to the 75 to 115 HP 2.1-liter Mercury FourStroke platform launched in 2014. Like the 3.0-liter and 2.1-liter platforms, the new 4.6-liter V-8 and 3.4-liter V-6 powerheads offer generous displacement for the class and a relatively uncomplicated design—no direct injection, no supercharging, no variable valve timing.

Both the V-6 and the V-8 arrange cylinders in a 64-degree vee, and they share a 92mm x 86mm bore and stroke. This gives the two engines some commonality in parts (pistons, for example) and in manufacturing process, which may help reduce cost. The V-8 engine is fitted with a balance shaft for smoother operation. Merc says the V-6 is naturally balanced and does not require the balancer. At 4.6 liters, the Mercury V-8 offers more displacement than the 4.2-liter Yamaha V-6 or the 4.0-liter Suzuki V-6. At a claimed 538 pounds (dry weight 25-inch length), the Mercury 300 FourStroke weighs 101 pounds less than a Suzuki DF300AP and 24 pounds less than a Yamaha F300. All of the new Mercury V-8 and V-6 models mount on 26-inch centers for multi-engine installations, especially handy for re-power situations when replacing older motors. Yamaha Offshore outboards require 28.5-inch centers.

A number of features of the Mercury V-8 are designed to ease maintenance. A chain cam drive runs in a oil bath and never needs maintenance (unlike a timing belt) and the “lash for life” valve train is designed to never require adjustment; it’s set forever at the factory. All of the V-8 models feature the “top cowl service door,” a water-tight hatch that covers the dipstick and the oil fill, so the oil level can be checked and topped off without removing the cowl. Also below the door is the latch release for removing the cowl that doubles as a carry handle to make it easier to lift and tote the cowl.

Top Cowl Service Door on Mercury V-8 models makes it easy to check the oil and lift off the cowl.

The current Verado L6 models set a high bar for quiet operation, and Mercury worked hard to match that standard. The new V-8 powerhead features a tuned multi-chamber air intake to

minimize airborne noise, special covers over the fuel injectors to mask that high-frequency sound, and a multi-chamber muffler on the idle relief system.

The new V-8 powerhead has all of the technology features introduced on the new V-6 engine. A “transient spark" calibration adjusts spark timing under acceleration load to boost torque by 5 to 7 percent, according to Mercury, and improve hole-shot performance. To improve fuel economy, the new V-8 models feature Advanced Range Optimization (ARO) and closed-loop fuel control, which work together to precisely adjust the fuel mixture and deliver the best-possible efficiency, on 87 octane fuel in each model. Adaptive Speed Control (ASC) maintains engine speed (rpm) regardless of load or condition changes – such as tight turns or tow sports – without having to frequently adjust throttle position. Idle Charge battery-management is designed to prevent draining batteries while operating multiple electronic devices. When battery voltage is reduced, the engine will automatically increase idle rpm to boost alternator output and recharge low batteries to the proper level. Like the V-6, the V8 powerhead has digital throttle and shift (DTS) actuators on the powerhead so models that do not come standard with DTS controls can be rigged with either cable or DTS at the customer’s choice.

The Verado and FourStroke V-8 motors are available in standard Mercury Phantom Black and at added cost in the three shades of white: Warm Fusion, Cold Fusion and Pearl Fusion. Factory-painted, polycarbonate accent panels will be available as kits (purchased separately) in gray, silver, blue and red for further personalization, and a primed panel will be offered for custom paint. While each outboard series (except for Racing) uses the same V-8 powerhead, there are distinct feature differences between each series.

mercury v-8 outboards

Verado V-8 models feature the Advanced Midsection (AMS) under the silver cover, which enables optional Joystick Piloting.

Verado 250/300

Positioned as the premium outboard product, these Verado models have some exclusive features. The Verado V-8 models weigh 600 pounds with a 20-inch shaft, 73 pounds more than a V-8 FourStroke model.

  • Advanced Midsection (AMS), like AMS on previous Verado models, is sort of an aluminum halo that supports the powerhead with perimeter mounts to provide maximal isolation of vibration from the boat. AMS is visually highlighted with a silver cover on the new Verado models.

  • Joystick Piloting requires the AMS and thus is only available for Verado models, as an option.

  • DTS and electro-hydraulic power steering are standard on Verado models. The power steering system is very similar to that designed for the L6 Verado models.

  • Only Verado models have “Advanced Sound Control” for the exhaust idle relief. The system is fitted with a pair of mufflers. When both are active the motors are very quiet at start-up and idle speed. But if the boat is rigged with a VesselView helm display or the latest SmartCraft gauges, the owner can choose to electronically bypass one of those mufflers to give the motor(s) a pleasant bark on start-up and a low V-8 rumble at idle and no-wake speeds. This is for the owner who also has loud “look at me” pipes on his Harley-Davidson. Once up to speed all exhaust exits underwater through the prop hub and the motor is very quiet.

  • A VesselView screen on the helm also enables an automatic oil level check feature that’s standard on the Verado V-8 models. When the keys are turned on a message pops up to report oil level in each engine. This only functions on cold start-up as the system can’t accurately check the level of hot oil. This feature is an option for V-8 and V-6 FourStroke models. A SmartCraft gauge will only issue a “low oil” alert.

  • Only the V-8 Verado models get a 115 amp alternator that makes 20 amps at idle.

  • The 5.44-inch diameter HD gearcase with a 1.25-inch propshaft is standard with a 1.85:1 gear ratio for the 250 and a choice of 1.85:1 or 1.75:1 for the 300. Both models are offered in 20-, 25- and 30-inch lengths.

FourStroke V-8 models have the Conventional Midsection (CMS) and fewer features than the premium Verado models.

FourStroke 250/300

These are “foundational” motors for buyers who don’t care to pay for all the Verado features. The powerhead and, I assume, the performance is about the same, or even a little better on smaller boats due to the weight advantage.

  • Conventional Midsection (CMS) has traditional motor mounts rather than the perimeter AMS mount system. Joystick Piloting is not available with the CMS.

  • Power steering and DTS are options.

  • Advanced Sound Control is not available on the FourStroke models.

  • Oil level check feature is an option.

  • Alternator output is 85 amps, with 20 amps available at idle.

  • The 5.44-inch diameter HD gearcase with a 1.25-inch propshaft is standard with a 1.75:1 gear ratio. Both models are offered in 20-, 25- and 30-inch lengths.

Designed for high-speed tournament bass boats, Pro XS models feature firm motor mounts and the hydrodynamic TorqueMaster gearcase.

Pro XS 200/225/250/300

Aimed primarily at tournament bass anglers, the Pro XS line takes the V-8 powerhead down to 200 HP (the Pro XS 175 has the 3.4-liter V-6 powerhead), and now tops out at 300 HP. Extra effort was made to reduce the weight of the Pro XS models. In fact, Mercury considered removing the 10-pound balance shaft from the Pro XS V-8 motors, but dropped that idea when the motors came in within 5 pounds of the 500-pound design target. A Pro XS V-8 weighs 22 pounds less than a FourStroke model.

  • The lightweight cowl is formed of low-density sheet molding compound (SMC).

  • All Pro XS models have the Conventional Midsection (CMS) fitted with higher durometer (harder) engine mounts for more precise control at high speeds.

  • Power steering is optional.

  • Pro XS models have a single muffler on the exhaust idle relief for that snappy bark on start-up and aggressive V-8 tone at idle and no-wake. There is no “quiet” option.

  • Oil level check feature is an option.

  • Alternator output is 85 amps, with 20 amps available at idle.

  • A TorqueMaster gearcase, designed for durability and high-speed operation, is standard on all Pro XS V-8 models, with a 1.75:1 gear ratio. The TorqueMaster features the 1.25-inch propshaft and extra water pick-ups on the nose cone that enable very high engine mounting, jack plates, and running at high trim angles. Bass boat stuff.

Phantom Black is the only color option, but there is an optional matte Pro Black accent panel available.

Designed to withstand the daily stress of commercial duty, SeaPro V-6 and V-8 models features a special calibration and heavy-duty gearcase. Joystick Piloting can be added to the SeaPro 300 AMS.

SeaPro 200/225/250/300

The SeaPro line of commercial outboards, which previously topped out at 150 HP, adds five new models using the 3.4-liter V-6 (SeaPro 200) and 4.6-liter V-8 (SeaPro 225 to 300) powerheads.

  • SeaPro models have a specific engine calibration that makes peak torque available at lower rpm, placing less stress on the engine for enhanced durability and enabling prop options with lots of blade area to push heavy loads.

  • The SeaPro 300 AMS is a Verado dressed for work, with the Advanced Midsection that enables Joystick Piloting, standard power steering and the 115 amp alternator.

  • SeaPro models with the Conventional Midsection have the 85 amp alternator and can be rigged with power steering.

  • SeaPro 200-to-300 HP models come equipped with a boat-mounted water-separating fuel filter kit, diagnostic SmartCraft gauges, and a graphic owner’s manual supplement.

  • A commercial version of the 5.44-inch HD gearcase is standard on all V-8 and V-6 SeaPro models, validated to three times the lifespan of a recreational gearcase, according to Mercury.

  • No color options for SeaPro models.

The Mercury Racing 300R has a modified 4.6-liter V-8 engine and is available with three gearcase options and other equipment choices. Shown here with the Sport Master gearcase.

Mercury Racing 250R/300R

The 4.6-liter V-8 gets the Mercury Racing treatment with these two new high-performance models, which will replace the 3.2-liter two-stroke V-6 250XS and 300XS models in the Racing outboard line. Both models have all of the powerhead features found on standard V-8 models, and are designed to perform on 87-octane fuel; the two-stroke XS motors they replace require 91 octane gas. Each can be rigged with mechanical or DTS controls, and power steering is an option. The 250R and 300R are offered only in the 20-inch length, while a 300R HD variant is offered in 20-, 25- and 30-inch lengths. These Racing outboards also come with a three-year warranty.

Racing 250R: This motor produces the same power as the 250 Pro XS but is equipped the Tri-ram Racing midsection with a high-durometer upper mount and solid lower mounts for enhanced handling at higher speeds, and it comes equipped with a Sport Master gearcase with a 1.75:1 gear ratio, low-water pick-ups and a crescent leading-edge design for maximized efficiency and speed. The WOT operating range is 5600-6200 rpm.

Racing 300R: There’s more tune-up on this motor, which features a Racing-designed intake with shorter runners, more-aggressive intake camshafts, an oil cooler and a re-calibrated ECU that takes the WOT range to  5800-6400 rpm. The standard 300R has the same Tri-ram Racing midsection and mount set-up as the 250R, but there’s also a 300R HD version with a heavy-duty midsection featuring solid upper and lower mounts, forged transom brackets with single-ram power trim and a remote trim pump designed to endure the harsh offshore environment. Select HD midsection models are equipped with an integrated rear tie-bar mounting plate for multi-engine installations. Optional side steering kits are also available for select high-performance applications. Three gearcase options are available for the Racing 300R: surface-piercing Sport Master for boats capable of speeds over 85 MPH; Torque Master for partial-surfacing applications and heavier bass boats;  the 5.44-inch HD gearcase for use on bay boats and multi engine performance center consoles where the application requires a more submerged gearcase. In the 20-inch length the 300R weighs 512 pounds, while the 300R HD weighs 546 pounds.

Written by: Charles Plueddeman
Charles Plueddeman is's outboard, trailer, and PWC expert. He is a former editor at Boating Magazine and contributor to many national publications since 1986.