America's Definitive Marine Engine Magazine
Mercury Verado began life on the water as a 2.6L inline, six-cylinder, four-stroke outboard available in 200, 225, 250 and 275 horsepower models. Not long after the company rather wisely upped the ante by adding three new 1.7 L models.
Mercury Verado supercharged inline fours are rated 135-, 150- and 175-horsepower. You've probably already figured out these are the six-cylinder motor minus the top two cylinders. Designed from a blank sheet of paper, none of the components are derived from automotive engines. That said, beneath the cowling, Verado is more than a little reminiscent of a race bred Porsche or Ferrari engine.
An inter-cooled supercharger flows a huge volume of cooled air into the combustion chamber. The colder the air the more oxygen available to light the fire. The greater the air volume, the higher the horsepower generated. A complex array of sensors monitor vital signs, juxtaposing horsepower, fuel economy and emissions against fuel quality, ambient temperature, coolant flow and altitude. Firmware advances the ignition timing and fine tunes the fuel/air mixtures right up to the razor's edge, brushing against the point of self destruction.
But a rock solid cylinder block and crankshaft hold the engine together when lesser creations would be pooling molten aluminum in the cylinder bores. More on that sturdiness later on in the story. When the electronic control module (ECM) responds to the call for more horsepower, it increases supercharger boost. Then the powerhead draws a big gulp of air thru state-of-the-art cylinder heads fitted with four valves per cylinder and twin overhead camshafts.
This combination of supercharger and a free breathing valve train guarantees horsepower comes on strong at all rpm. But particularly at low and mid-range where an engine logs a considerable number of hours. Low end potency is an important characteristic for a four-stroke, because compared to two-strokes, they tend to be anemic at lower rpm. The reason why is as simple as the sea is salt. A two-stroke fires with every turn of the crank, whereas a four stroke only fires every other revolution. More power strokes equals more torque.
To compensate, outboard builders deepen the four stroke gear ratio to multiply the torque at the prop shaft. In other words the engine turns a higher rpm for a given speed. But the four-stroke Verado gear set ratio remains a fairly conservative 2.08 to one, or about what you'd expect to find on a two-stroke. That's because maximum torque comes on strong at about 4500 rpm, with an operating range of 5800 to 6400 rpm. According to Mercury's dyno men, Verado outboards match two-stroke performance at any rpm.
Engine reliability is a characteristic worth visiting. Just like the first generation, inline six-cylinder models, four-cylinder Verado's major castings (lost foam process) are state of the art creations. At the foundry molten aluminum flows into the mold under extreme pressure, forming dense component. With molecules packaged so tightly tighter, components boast great strength and light weight. The closed-deck cylinder block isn't handicapped by a gap between cylinder walls and deck. That makes it stiffer. Conventional cylinder head bolts are replaced by special fasteners that attach from below, substantially stiffening the assembly. Just like an extreme high rpm Formula One race engine, the newest Verado girdles its crankshaft main-bearing journals with a reinforcing plate. Oil galleries in the pistons pull heat out of the skirt for longer life and maximum horsepower. All these myriad of things add up to an ultra stiff assembly and a long life
Curiously, even with all this high performance horsepower there is no monster's roar. The nearly whisper quiet Verado idles at a barely audible 52 decibels. At wide-open throttle it purrs at 86 decibels, a voiceprint so quiet that wind and waves sometimes sound louder than the engine.
Verados come rigged with Mercury's Digital Throttle and Shift system (DTS)—a fly-by-wire control system. User friendly DTS communicates directly with the engine control module (ECM) to more precisely actuate speed and gear changes. Throttle shift action is delightfully smooth and devoid of hesitation. Unlike mechanical cables there's absolutely no resistance or backlash. Even better than DTS proper is the built-in automatic engine synchronizer which allows the helmsman to concentrate on running the boat instead of studying tachometers and adjusting individual the throttle levers.
Another vital component part of the four-cylinder Verado package is the Mercury Universal Steering Cylinder. One must-have option is the electro-hydraulic power steering, similar to the 200-275 hp Verado, that mates to a power steering pump with the universal cylinder.The low drag lower unit optimizes both acceleration and top speed. Fitted with upgraded bearings and prop shaft seals its durability matches that of the powerhead. The Advanced Midsection (AMS) progressive-rate mounting system cradles the powerhead at its center of gravity for less vibration. Another nice touch, the trim angle is programmable. Finally, Verado's are skinny, in-line engines, a characteristic which pays big dividends when rigging twins and triples on a narrow transom.