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Yanmar 8SY-STP
900 HP Marine Diesel

Yanmar 900 hp marine diesel

More Horsepower for Big Boats

You probably noticed how Yanmar Marine has been busy the past few years, releasing a flurry of new marine diesels.

One of the most interesting is a potent, 16-liter torque monster dubbed the SY-STP. Its rating: A whopping 900 horsepower. Given its Jovian proportions it should come as no surprise to learn the new motor is specifically intended for high performance cruisers and motoryachts, big, fast boats. If Rudolph Diesel were alive today, his jaw would drop in amazement to see how far his wunderkinden has evolved. Point of history, Diesel’s first prototype burned coal dust.

Meanwhile, back, in the new millennium, this new found Yanmar 8SY-STP is a 90º V-8, a proven cylinder block design that yields a boatload or horsepower without adding unnecessary weight. Diesels are inherently heavy, so the lighter the better.

The Yanmar Marine fuel system, replete with twin turbochargers, maximizes torque at low rpm so acceleration comes on stronger, and is more on par with gasoline engine performance. Compared to previous generations, fuel economy is improved, a personality trait that reduces operating costs at the same time it extends range. Truth be known, most boaters don’t save money with a more fuel-efficient engine. Instead they spend their good mileage dividend by traveling further from homeport and staying out on the water longer.

More efficiently converting diesel fuel into forward motion also pays big dividends for the environment. Emissions are reduced. That means the ride is more comfortable for captain and crew, and the air we all breathe stays cleaner. There’s no secret how Yanmar’s engineers accomplished this good mileage-clean air feat. As mentioned early on, twin turbochargers force feed cooled air into the cylinders. Cool air is dense, which allow the turbo to pack an even greater volume of molecules into the combustion chamber. The net effect is like adding cubic inches, so the engine behaves like it’s bigger than its displacement.

Also important are the four valves per cylinder that cheat the laws of physics. Once again we see a technology that allows a freer flow of air into and out of the combustion chamber. Two narrow intake and exhaust ports, as opposed to two cavernous ports, maintain high air velocity. That improves throttle response.

Yanmar 8SY-STP is an electronic diesel, fitted with electronic fuel injectors (EFI) that meter the precise amount of diesel injected and time the pulse to the exact millisecond it ought to be introduced into the fire. EFI does this from the first instant of a cold start, through idling, and on up the rpm band to wide-open throttle (WOT). It’s this precise metering of diesel fuel, and the optimal moment of injection that generates such a lofty output. At the same time diesel consumption remains miserly because the firmware knows exactly how to squeeze every last drop of horsepower out of a fuel molecule.

There’s even more good news to report from Yanmar Marine. This configuration emits less visible exhaust smoke. In fact, during recent testing of one of these great beast I could not see or smell even a whiff of smoke. Neither did I hear the characteristic diesel clatter. It too had been vanished.

Obviously what makes the electronic fuel injection tick is a sophisticated engine management system, one that constantly monitors and processes vital engine data such as rpm, turbocharger boost pressure, coolant temperature and throttle position. Firmware (a computer program) reads data then adjusts injection timing and the amount of fuel injected as necessary. The engine communicates in an Esperanto called CAN, short for communications area network. CAN bus protocol is an industry standard that permits a total overview of the engine data in real time.

Nothing manmade lasts forever, not even a state of the art diesel. So I was pleased to see how the Yanmar 8SY-STP features individual cylinder heads that are light enough in weight to be removed and replaced by a lone mechanic. That’s a valuable characteristic for a number of reasons. Sometimes the valves in just one cylinder burn while the other five remain healthy. So if only one head has to be serviced then naturally it follows labor and parts will be significantly less expensive than the costs of rebuilding a full-size cylinder head. Plus, it’s easier to remove one little cylinder head than a hulking big one, no matter whether in a stooped over in cramped engine room or in a space big enough to play handball. An added benefit, the modular design cuts down gross engine weight, approximately 3,637 pounds fully-equipped.

Scheduled maintenance is made easier by easily accessible service points (crankcase oil dipstick, et cetera). In the unlikely event anything should go haywire, troubleshooting is straightforward thanks to the electronic diagnostics programmed into the firmware. The bottom line: Routine engine care is simple and economical.

This engine measures a compact 51 long x 49 wide x 42 inches, compact dimensions that make front-end mounting of power take-offs for other engine-driven equipment easy. Fresh water cools the entire engine and the charge-air cooling for the turbo boasts an extra circuit for the coolest possible air flow.

Finally, the 24-volt 140-amp high capacity alternator is the perfect match for a total battery capacity of about 160 amp-hours. That’s enough capacity for a full array of onboard electronics like Radar, GPS, VHF, depth finder and sound system.

Yanmar Marine 8SY STP Specifications:
Horsepower 900 @ 2300 rpm
Displacement 15.6 Liters
952 CID
Cylinder Configuration 90 Degree V-8
Bore x Stroke 5.0" x 6.1"
Weight 3650 Lbs
Combustion Direct Injection