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Mercury Racing Launching Four-Stroke Formula One Tunnel Boat Outboard

Diehard go-fast boating fans and gearheads in general can stop wondering what Mercury Racing will do next with its four-stroke V-8 outboard engine program. Exclusively available for order to qualified Formula One tunnel boat teams competing on the Union International Motonautique F1H2O World Championship circuit, the 360 APX outboard is the latest V-8 creation from the Fond du Lac, Wis., high-performance marine engine and accessories company.

New from Mercury Racing, the 360 APX four-stroke V-8 outboard is designed for the F1H2O World Championship series, which was claimed by Team Abu Dhabi in 2018 and 2019. Photo courtesy Arek Rejs/F1H2O.

Mercury Racing announced the news in a press release this morning.

“The 360 APX will usher in a new era of performance for this premier class of tunnel boat racing,” said Stuart Halley, the company’s general manager, in the release. “It combines a durable, low-emissions, four-stroke powerhead with amazing performance, and will require much less maintenance than the two-stroke outboard currently in use in the F1H2O World Championship.”

The gold standard in powerboat racing circuit competition and professionalism, the six-race F1H2O series attracted nine teams with 18 drivers from 12 countries in 2019. Florida native Shaun Torrente of Team Abu Dhabi claimed the title for the Emirate nation in 2018 and 2019. The 2020 F1H2O season was postponed in response to the COVID-19 pandemic.

Look for a follow-up interview with reigning two-time F1 H2O world champion Shaun Torrente on speedonthewater.com later today.

Producing 360 hp at the propeller shaft, the naturally aspirated 360 APX is based on a modified version of the Mercury Racing 300R 4.6-liter V8 powerhead, according to the release, and the engine retains its double overhead cam/four-valve architecture. The compression ratio is increased from 10:1 to 11:1 and peak engine operating speed is boosted from 6,400 rpm to 7,000 rpm in the 360 APX version.

The powerhead is fitted with a short-runner intake manifold mated to a cold-air induction system vented through the cowl. The engine calibration is modified to take full advantage of the powerhead modifications. The 360 APX uses a 24-volt starter for faster dock-side starting in competition. A digital control offers smooth and precise throttle application.

In addition, according to the release, the 360 APX offers 90-percent-lower emissions than current two-stroke racing engines and was designed, according to UIM president Raffaele Chiulli, with “input from the UIM and H2O racing.”

“I am excited about the arrival of a new low-emissions competition outboard engine from Mercury Racing, focused at the top level of powerboat racing,” Chiulli said. “The engine significantly reduces exhaust emissions while at the same time providing the speed and excitement that powerboat racing fans expect from our flagship series in circuit racing. The UIM supports full implementation of this engine, which demonstrates our commitment to lowering carbon levels in our sport.”

Designed on a clean sheet, the engine’s all-new 12-inch midsection was specifically created for Formula One tunnel boat applications, with a structural wet sump driveshaft housing and integrated power trim and lift with remote pumps. An overdrive spur gearset between the crankshaft and the gearcase increases the input shaft speed to the gearcase to match that of the current 9,600-rpm two-stroke race engine, and produces the left-hand propeller rotation desired for Formula 1 circuit racing. The overdrive gears are designed to accommodate multiple gear ratios, so the teams can select the ratio that best fits each particular race.

“The primary purpose of the overdrive is to increase the input speed to the gearcase,” said Jeff Broman, Mercury Racing’s director of engineering, in the release. “While the 360 APX produces about 45 percent more torque, it doesn’t match the engine speed of the 2.5-liter two-stroke. With the new 360 APX we can trade some torque to increase propeller speed via the overdrive, which will also improve the life span of the gears.”

An evolved version of the Mercury Racing Super Speed Master (IV SSM) outboard gearcase is direct-drive with no neutral or reverse shifting. Above-water exhaust offers unrestricted flow and produces an “exciting tone for racing fans.” The outboard boasts integrated lightweight steering arms for tunnel boat cable steering. The top cowl and driveshaft housing covers are lightweight carbon-fiber composite. The cowl features robust latching and sealing systems, while the driveshaft cover has quick-release fasteners to ease access to the midsection.

Mercury Racing 10W-30 MRX engine oil, a new high-performance full-synthetic lubricant, was engineered alongside the Mercury Racing 360 APX outboard and specifically formulated to withstand the extreme heat and stress the engine will encounter during F1 tunnel boat competition.

Shipments of the Mercury Racing 360 APX outboards are expected to begin in early November 2020.

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