DF300AP

In multi-outboard installations on large boats, a counter-rotation outboard is usually paired with a regular rotation model to help keep the boat traveling on an even keel and in a straight line. The DF300AP/250AP is built with special counter-rotating gearing in the lower unit, which causes the prop to rotate in the opposite direction. Suzuki Selective Rotation eliminates the need to purchase a dedicated counter-rotation outboard by using a special switch that when connected to a circuit inside of the engine compartment, turns a regular rotation outboard into a counter-rotation model with a counter-rotational propeller.* This industry first is made possible through a special, unified design of gears, shaft, and bearings in the lower unit that are designed to operate reliably and efficiently in either regular or counter-rotation directions.

Compared to the original DF300, the biggest changes you’ll find on these outboards are in the lower unit, which was redesigned for the Suzuki Selective Rotation system — the world’s first integration of regular and counter-rotation models into a single unit. The system consists of a new drive gear layout in the lower unit that allows the outboard to operate in either regular or counter-rotation mode and a switch that connects to a circuit in the engine compartment that engages the counter-rotation mode.

Like the DF300, the DF300AP/250AP utilizes an aggressive final drive ratio of 2.08:1 allowing it to turn a 406mm (16-inch) diameter propeller available in various pitch size for optimum performance on a wide variety of boats. Changes to gear designs provide greater durability, and adding a two-way water inlet changes water flow into the cooling system for increased cooling efficiency.

The DF300AP/250AP features a redesigned low drag gear case developed to accommodate the new gears utilized in the Suzuki Selective Rotation system.

The case itself is actually larger than the previous model to provide increased gear durability, however it is designed with a smoother, more hydrodynamic shape that allows it to move through the water with less drag and greater efficiency. Areas with the highest drag are indicated in red in the illustrations below. The comparison shows that the new design allows the lower unit to slice through the water with less drag.

Suzuki’s innovative Lean Burn Control System was first introduced on the DF90A/80A/70A to great acclaim from boaters and the media alike. It predicts fuel needs according to operating conditions allowing the engine to run on a more efficient fuel mixture through the use of a lean air-fuel ratio. It delivers its benefits over a wide operating range, providing significant improvements in fuel economy from low-speed operation into the cruising range. Combining this system with the Suzuki Precision Control electronic throttle and shift system allows the operator precise control over engine RPM for improved fuel economy over a wider operating range. This combination also delivers smooth power transitions throughout the entire RPM range. In-house testing shows that while cruising, the DF300AP is 14% more economical than the original non-Lean Burn DF300 without sacrificing any power of the original DF300.

Suzuki’s engineers designed the 4.0-liter V6 engine with an aggressive cam profile that delivers maximum output and performance at high rpm. In coupling this cam profile with Suzuki’s advanced Variable Valve Timing (VVT), the DF300AP/250AP delivers the additional torque that outboards need for accelerating in the low to mid-range. VVT achieves this by adjusting the timing of the intake valves, allowing them to open before the exhaust valves are fully closed, creating a momentary overlap in the timing where both sets of valves are open. Using VVT, this overlap can be increased or decreased by altering intake timing with the camshaft resulting in optimum timing for low and mid-range operation.

Another performance enhancing feature on the DF300AP/250AP is a tuned long track intake manifold. Using long intake pipes tuned to provide smooth airflow into the engine the system provides the DF300AP/250AP with enhanced low-end power.