Yanmar enters the sterndrive engine market with the ZT350

After many years of the two-party system, there’s now a third choice. No, not for president, for your sterndrive propulsion needs. This year, Yanmar is entering the market alongside MerCruiser and Volvo Penta, with the Yanmar ZT350 Sterndrive system.
 Although Yanmar diesels have been paired with MerCruiser sterndrives in the past, and will continue to be available to those who want them, Yanmar wanted to offer its customers a Yanmar-only option. “Sometimes when you get two companies involved, there tends to be some finger-pointing when issues crop up, and occasionally customers get caught in the middle,” said Tom Watson, Yanmar’s manager of sales and marketing. “We wanted to be in control of our destiny and be able to offer a complete package.”  

The Biggest Loser
 Historically, diesels have been impractical for smaller pleasureboats, because they weighed too much. But when the ZT350 is mated with Yanmar’s BY series diesel powerplant, which uses a marinized BMW block, the weight is comparable to that of many popular gas engines. Together, the 260 hp 3.0L six-cylinder 6BY260Z and the ZT350 outdrive weigh 930 pounds – even counting the engine’s twin counter-rotating stainless steel props. Yanmar accomplished this weight savings with features including aluminum cylinder heads, plastic valve covers, a ribbed cast-iron block and a heat-tempered hollow crankshaft.

Computer Control
 As we enter a new era of reduced sulfur diesel and lower U.S. cetane levels, which is the measure of a fuel’s combustibility, some problems can develop. Fortunately, Yanmar’s Electric Control Unit (ECU) can adjust to the various fuel qualities boaters see worldwide. In addition, the ECU directs the common-rail fuel-injection system to adjust for differences based on engine speed, load and acceleration. And for quick starting, Yanmar’s dual-injection technology squirts a small amount of fuel into the cylinder before the main charge, which also cuts down on excessive start-up noise.

Torqued Off
 Once in open water we got a chance to open it up. At first it was a little disappointing when compared to the instant kick you get from gas engines. We experienced a fair amount of bowrise before the intercooled turbochargers kicked in and the action really began. Our time to plane was a stately 8.6 seconds, but about halfway through, a surge of turbo power hit and we felt the massive torque push the bow over as we accelerated to 30 mph in 12 seconds. The acceleration continued until we hit a top speed of 44.9 mph.
 Looking at the torque curve graph of the 6BY260Z is revealing. Until the engine reaches 1500 rpm, not much is going on, then, to quote Emeril, “Bam,” the line starts heading skyward and you get right into the meat of its pushing power as it develops 400 foot-pounds of torque at 2500 to 3000 rpm. From 2000 to 4000 rpm, the engines make a minimum of 340 foot-pounds of torque, giving you a fat, plateau-like power curve. This amount of torque is a huge advantage for those who travel most often just above planing speeds. Econo-cruising is what diesels do best, and their longevity also goes way up when run at moderate speeds.  BW