Bigger Four-Strokes<br /><br />By Jim Barron <br />2003-02-01<br /><br />Both Mercury and Suzuki are on the verge of introducing the most <br />power-ful four-stroke outboards ever<br /><br />Both Mercury and Suzuki are on the verge of introducing the most <br />power-ful four-stroke outboards ever, and we've got some juicy <br />details.<br /><br />First, lets talk about Mercury Marines new 250 hp four-stroke known <br />at Mercs Fond du Lac, Wisconsin, headquarters as Project X. We had a <br />chance to see, photograph and run prototypes on Tennessees Percy <br />Priest Lake. <br /><br />Though we were not allowed to look under the hoods or do any detailed <br />testing, we found the engines every bit as impressive as the V-6 four <br />strokes from Honda and Yamaha. The engine is quiet and powerful, <br />capable of pushing a Triton TR21 bass boat to 69.9 mph on a cold, <br />blustery day. A 22-foot Angler center console was pushed into the <br />upper 40s with four persons aboard and the fuel gauge reading two-<br />thirds full.<br /><br />Easily observable features of the engine are an integral hydraulic-<br />steering system that does not require a drag link from a hydraulic <br />cylinder to the tiller arm. This makes for a neater and more compact <br />steering system, particularly in <br />twin-engine installations. The Mercury hydraulic system was designed <br />to work with a Teleflex Sea Star helm pump. The engine also <br />incorporates Mercurys new Digital Throttle and Shift (DTS) a fly by <br />wire control. The elimination of looped shift and throttle cables <br />tidies up the stern section. Also, the engines clamp bracket has been <br />redesigned along with a new power-trim system. The new four-stroke <br />also features a redesigned lower unit, weve been told.<br /><br />ALL CHARGED UP<br /><br />Mercury admits that the engine is pressure charged, meaning that it <br />is either turbocharged <br />or supercharged. We could not detect any turbo whine. The low-end <br />wallop and sharp throttle response indicates that the engine is <br />supercharged. Holeshot is stronger than any other large four-stroke <br />engine in fact, its equal to most two-strokes in this horsepower <br />range. <br /><br />Though Merc staff were officially mum, we were able to glean key <br />internal features. According to inside sources, the 250 hp four-<br />stroke is an I-6 displacing 2.6L. It features dual-overhead cams and <br />four valves per cylinder. The engine has <br />a relatively flat horsepower curve, and maximum torque occurs at 4500 <br />rpm. The engine is rated to turn between 5800 to 6400 rpm, though the <br />valve train is designed for engine speeds in the 7000 rpm range, <br />leaving a generous margin for safety if someone pushes the redline or <br />disables the rev <br />limiter. Our sources tell us that the actual propshaft horsepower is <br />266 at 6000 rpm. Officially a 2004 product, we expect to see the 250 <br />at dealers by midyear.<br /><br />Other 2004 products are three new midrange OptiMax outboards. These <br />will be three-cylinder engines rated at 75, 90 and 115 hp. All will <br />displace 1.5L, and are based on one half of the 3.0L OptiMax V-6 <br />block. This means that the outboards can share common internal parts, <br />such as pistons, connecting rods and bearings, plus some external <br />parts, such as the fuel rail and injectors. We had a chance to run <br />the 115 hp version. It starts easily, idles smoothly and doesnt <br />smoke.
