Suzuki Marine's DF300A Outboard

Selective Counter-Rotation and New Engine Management Firmware

A few years ago Suzuki Marine introduced the world's first production 300-horsepower, 4-stroke outboard motor, the DF300. Now we are blessed with the arrival of the 300-horsepower outboard's second generation, the DF300A. For more information about the original engine, which provides the basic building block for the new DF300A - click here -

Suzuki DF300A outboard motor

The biggest upgrade found on the new motor is the lower unit which has been re-engineered for counter-rotation. In other words, a DF300A can spin its propeller either clockwise or counter-clockwise, depending upon how it was rigged. Out of the shipping container, all that's required to change a DF300A to counter-rotation is to flip a switch under the cowling. Suzuki calls this feature Selective Rotation. And with Selective Rotation the need to purchase a dedicated counter-rotating outboard motor disappears.

The gears proper were upgraded to a larger diameter, a tougher alloy and heat treated. You already know this scenario pays big dividends in durability. And even though the gearcase casting was made bigger in order to accommodate the larger gearset, its hydrodynamic profile is more efficient resulting in less drag. Another upgrade is the addition of a second water inlet for flowing a larger volume of coolant to the powerhead.

Besides lower unit work, the powerhead has also been lovingly bestowed with new technological accoutrement including Lean Burn firmware and an O2 sensor. The O2 sensor reads the composition of the exhaust gas, which gives it a sneak peak into exactly what's going on in the combustion chamber. With every exhaust stroke of a cylinder the sensor reads whether the combustion is running rich or lean. Within limits, the leaner the air-to-fuel ratio, the better the mileage and the lower the emissions. Lean Burn uses this information, along with throttle position, crankshaft position, intake air temperature, cylinder wall temperature and other variables to adjust ignition timing and fuel flow.

One must-have engine option is the trolling system that works from idle up to 1200 rpm. Like a tow vehicle's cruise control, it keeps the boat moving at a constant speed by tweaking engine revs in 50 rpm increments. Troll Mode includes a tachometer and a control switch that can be mounted anywhere on the console.

Author Timothy Banse has published articles in Popular Mechanics, All Chevy, Pickup Van & 4-Wheel Drive, Mecanica Popular, Motor Boating, Yachting, Mar y Vela and many other magazines and newspapers from around the world. He writes about cars, trucks and tow vehicles and marine-engine technology.