Tunnel-boat racers in the Union International Motonautique F2 and American Power Boat Association OPC ranks have a powerful new low-emissions outboard engine option in the form of Mercury Racing’s 200 APX model. The first four-stroke, V-6 outboard produced by the Fond du Lac, Wis., company, the APX 200 delivers 200-plus hp while reducing exhaust emissions 50 percent compared to those produced by the Mercury Racing’s 200 XS OptiMax outboard and 90 percent compared to those of its legacy SST 120 offering.
Mercury Racing’s first V-6 four-stroke outboard engine, the 200 APX is designed for tunnel-boat competition. Photos courtesy/copyright Mercury Racing.
The engine will be available next month, according to a press release from Mercury Racing this morning.
“The new 200 APX is designed to deliver outstanding performance while reducing the cost of maintenance and fuel for race teams,” said Stuart Halley, Mercury Racing’s general manager, in the release. “Mercury Racing is also striving to produce high‑performance and competition engines that keep emissions to a minimum, and the 200 APX helps push that effort forward.”
The 200 APX powerhead is based on the Mercury Marine 3.4‑liter, double-overhead-cam, four‑valve powerhead with a 64‑degree cylinder angle. To prepare the engine for competition, Mercury Racing ups the compression ratio from 10:1 to 11:1, increases peak engine speed from 5,800 to 6,800 rpm, and fits a lightweight carbon fiber cowl that incorporates forced cold air induction, according to the release.
A lightweight flywheel allows the engine to rev more quickly than the stock motor. The engine requires readily available 91‑octane (98 RON w/ E10 max) pump gasoline fuel. The 200 APX retains a digital throttle control and is equipped with a 24‑volt starting system.
The 200 APX uses the same robust 12‑inch midsection as the Mercury Racing 360 APX V8 competition outboard, with a structural wet sump driveshaft housing and integrated power trim and lift with remote pumps. To increase propeller speed to match that of the 8,000‑rpm two‑stroke racing outboard presently used in F2 and OPC, an overdrive spur gearset increases the input shaft speed to the gearcase and produces the desired left‑hand propeller rotation.
“The 200 APX produces about 20 percent more torque than the two‑stroke motor, but at a lower RPM,” said Jeff Broman, Mercury Racing’s director of engineering, in the release. “With the overdrive gearset we can swap some of that torque to increase propeller RPM, which allows most teams the opportunity to use the same propellers they have been fitting to the two‑stroke motor—a big cost savings for the race teams.”
The engine boasts an “evolved version of the Mercury Racing Super Speed Master (IV SSM) outboard gearcase,” a direct‑drive unit with no neutral or reverse shifting. Above‑water exhaust offers unrestricted flow and produces an “exciting tone for racing fans,” according to the release. The motor is equipped with integrated, lightweight steering arms for tunnel boat cable steering. The top cowl features robust latching and sealing systems, while the carbon fiber driveshaft cover has quick‑release fasteners to ease access to the midsection.