6 Of The Most Powerful Outboard Boat Engines Ever Built

SlashGear has traditionally focused on advancements in terrestrial transportation like cars and motorcycles, but we've devoted plenty of space to discussion of marine engines as well. We've presented a guide to Yamaha outboard motors, a similar primer on boats powered by electric motors, and a spotlight on General Motors' partnership with a hybrid marine engine manufacturer. Most marine engines fall into one of three formats. Many recreational boats use outboard motors, which mount to a watercraft's transom and have a propeller shaft mounted perpendicular to the driveshaft. 

Outboard motors are used to steer the boat as well as move it through the water. Inboard motors are mounted near the boat's center and rely on rudders to steer the craft, and a stern drive motor (also known as an inboard/outboard) has an internally mounted power unit connected to a drive unit that houses the propeller and steers the boat. Outboards have come a long way in recent decades in terms of efficiency and output since the days when carbureted two-stroke engines were the norm. Bombardier Recreational Products bought the venerable outboard brands Johnson and Evinrude in 2002 and developed the "E-TEC" direct-injection outboard under the Evinrude name. 

That motor maximized power output while also winning an EPA Clean Air Excellence award, and Bombardier followed that up with the "Ghost" series, an adaptation of the Rotax engines used in personal watercraft and small airplanes. Evinrude's most powerful current engine makes an impressive 300 horsepower, but there are a handful of engines on the market that leave that motor in their wake.

Honda has been making motors for automotive and motorcycle use for decades, but Honda's only current production V8 engine is the BF series marine outboard. The four-stroke engine family ranges from the 57.2cc, 2.3-horsepower BF2.3 to the BF350, a 5.0-liter beast that puts out a name-appropriate 350 horsepower. That's more than all but two of Honda's most powerful automotive engines ever, and enough to move all but the largest and heaviest of boats. The BF350 uses a specially designed crankshaft to run with minimal noise and vibration, and has cruise control as well as motorized trim and tilt functionality.

It also has a 70-amp alternator to keep the battery charged while running fish finders, communications equipment, and on-board entertainment systems. The water-cooled four-stroke engine has its two banks of cylinders mounted at a 60-degree angle, and features Programmed Fuel Injection and Honda's VTEC variable valve timing and lift control. The price of this formidable engine varies by location, but expect to pay at least $30,000 to bolt a BF350 to the back of your boat.

Suzuki has been around since 1909, and built its first engine, a 36cc two-stroke motor for bicycles, in 1952. Suzuki's first outboard was a two-stroke, 5.5-horsepower outboard that debuted in 1965, and the company's best current boat motor rivals that of Honda, its longtime competitor in the motorcycle and automotive realms. The 350-horsepower DF350 AMD was introduced at the 2022 Fort Lauderdale International Boat Show and released as a 2023 model, alongside the 300-horsepower DF300BMD. The companion four-stroke V6 models have a newly engineered lower gear case that drives the twin propellers and allows for less water resistance and easier gear oil changes.

Both engines also feature a new air intake system, dual fuel injectors, variable valve timing, and a self-adjusting timing chain. These advanced features make the DF350 AMD even more expensive than its 350 horsepower Honda counterpart. The Suzuki powerhouse starts at $47,250, although Suzuki Marine offers financing starting at $164 per week.

Yamaha is another of the top four companies on our list of major motorcycle manufacturers that translated that two-wheeled success into powerful outboard boat motors. Yamaha's most powerful current model is the 450-horsepower, 5.6-liter XTO Offshore V8. It takes that mantle from the previous 425-horsepower XTO, and gains the extra 25 horses from a higher compression ratio of 12.3:1 (versus 12.2:1 for the XTO Offshore 425). Both models feature electric steering and a Phase Angle Control charging system that provides 96 amps of juice at idle and up to 400 amps at higher engine speeds. The direct fuel injection system operates at pressures up to 2,900 pounds per square inch, ensuring a robust and steady supply of gasoline.

The XTO Offshore series motors run on 89 octane gas, allowing you to save a little money with each fill-up. That saving will be helpful, because the XTO Offshore 450 ranges in price from $49,500 to $54,200.

Elmer Kiekhaefer floated unknowingly into the outboard motor business when he purchased a bankrupt Wisconsin manufacturing company in 1939. In its warehouse, he found 300 motors in need of repair, which he fixed and sold. He launched the Mercury brand the next year, and built the world's first six-cylinder outboard motor in 1956. Mercury has continued to develop powerful outboards since then, and produced the world's first V6 outboard motor in 1976. 

Mercury's current line includes the 500R, a 4.6-liter V8 that makes as much as 500 horsepower thanks to a supercharger and 92 mm throttle body. Among the 500R's advanced features is a system that senses the humidity through the air intake and calibrates engine performance accordingly. The pilot also enjoys a digital throttle control and shift system, as well as an adaptive speed control that reacts to changing currents and wind conditions. The 500R also supports Mercury's SmartCraft suite, which includes telemetry and navigational tools.

Mercury hasn't stopped with the 500 hp V8. The company also makes a 7.6-liter V12 monster that churns out 600 hp and also works with the SmartCraft system. The Verado V12 comes with a 150-amp alternator to keep the Smartçraft system running even at idle, and runs on 87 octane gasoline or 10% ethanol fuel. The naturally aspirated motor made boating history as the first-ever V12 outboard and the first outboard motor to come with a two-speed automatic transmission. It comes with a top hatch to allow you to check and fill the oil and perform all the 200-hour service checks while still in the water, and Mercury's proprietary advanced mid-section setup helps isolate vibration from the powerhead to make your ride as smooth as possible. 

It also has a pair of contra-rotating propellers and a gearcase that moves independently of the powerhead for unmatched maneuverability. Boat Test mounted the Verado V12 on a variety of big, heavy boats to test its real-world performance and found that "the power came on smooth and linear." On the Formula 500 Super Sport Crossover – a 50-footer weighing 43,400 pounds — the Verado managed to get to 20 miles per hour in under eight seconds and to a top speed of 69 miles per hour.

Like the other powerful motors on this list, the Verado V12 will set you back quite a bit. The 30-inch shaft model sells for $82,205, and the 35-inch version has a retail price of $83,195.

The output and design of the Mercury Verado are no doubt impressive, but you could recently buy an outboard motor that was even more powerful. Seven Marine made a line of V8 boat motors that ranged from 527 to 627 horsepower. They were based on the General Motors 6.2-liter V8 that powers the Corvette Stingray. While the Corvette's V8 is naturally aspirated, the Seven Marine 627SV employs a supercharger. So equipped, it produces 813 Nm (600 lb-ft) of torque to smoothly move big, heavy boats. It came with the buyer's choice of three gearcases, two of which featured counter-rotating propellers. Trim settings and telemetry are displayed on a customizable TEC7 touchscreen display, which also has buttons to start and stop the engines.

Unfortunately, the Seven Marine powerhouse V8 is no longer available. The Volvo group purchased a majority stake in Seven Marine in 2017 and decided that Seven's environmentally unfriendly gas chuggers didn't have a place in a more sustainable future. If you're lucky enough to have purchased a 627SV while they were still on sale, Volvo is still providing warranty and parts support.