American car racing legend Dan Gurney's patented Moment-Cancelling Four-Stroke (MC4S) engine features two counter-rotating crankshafts and an innovative intake system. With it, Gurney is looking to conquer the Holy Grail of internal combustion engines: reliability, efficiency and low emissions, all in a single design targeted at motorcycles, but which could also be used in cars, planes and boats.
The inventors of the new engine, Dan Gurney and his collaborator and former competitor Chuck Palmgren, believe that despite 120 years of development, the four-stroke engine hasn't been able to make significant advancements in addressing two fundamental problems: optimum combustion and user-friendly operation.
"I'm not anti-electric automobiles," says 84 year-old Gurney. "The fact is that there are global and US oil and gas fields available which should last for many, many decades, I want to have a go at making the internal combustion engine even more competitive with electric power for some of those decades."
His patented design stands out by incorporating a twin crankshaft configuration that we haven't seen in the motorcycle industry for many years. Its roots reach as far back as the 1910s, to Bugatti's airplane U-Engine. But in the motorcycling world its most notable early appearance would be in the Ariel Square Four from the 1930s, while younger generations probably remember Suzuki's RG500 and Kawasaki's KR250 and 350 two-stroke racers from the late 1970s and early 1980s.
For Dan Gunrey, this layout is the best way to build a motor that self-cancels vibrations, which is a structural problem in every internal combustion engine.
"Without special balancing systems, vibration and reciprocating engines go together," he explains. "My experience is that things vibrate for a while, then fatigue and fall off or fall apart."
The MC4S engine is a tandem twin – the two cylinders are positioned along the axis of the frame – with a different crankshaft for each cylinder. As the two shafts rotate in opposite directions, their moments balance each other out, thus eliminating the need for balance shafts and making for a simpler structure with fewer moving parts.
Each crankshaft is shorter and sturdier and allows the engine to be more compact. Weight-wise, the second crank more or less evens out the balancing gear that has been removed. This design should benefit the bike's handling as the moment-cancelling nature of the engine promises a completely neutral feeling when the motorcycle tips into a corner.
But that's not all. As we delve deeper into the patent description, things get even more interesting. Gurney ventures into the world of optimal combustion by designing the intake system with an oversquare cylinder (piston bore larger than its stroke) and a meticulously calculated relationship of the intake valve area to the bore area.
The intake port has a "double tapered" cross section, as its diameter gets thinner in the middle section, forcing the flow to accelerate, before gradually expanding to meet the exact valve seat size. Playing around with small variations in intake port diameter and inclination, as well as valve seat angles, results in what Gurney calls the "optimized taper configuration" and some astonishing output results.
The first prototype engine to be built will be the liquid-cooled tandem twin (pictured above), with a displacement of 110 cubic inches (1,800 cc), two overhead camshafts and four valve heads. According to the simulations that Gurney has run, the MC4S engine with a standard straight intake port will produce 141 hp (105 kW), while the output of the very same engine with the special porting system skyrocketed to 262 hp (195.4 kW); that'd be an 85 percent increase, from a naturally aspirated engine burning normal pump fuel. According to the patent text, this is simply the result of delivering the air deeply and efficiently into the bore to enable a more efficient combustion process.
But the simulations produced even more surprising results. Measurements of the Brake Mean Effective Pressure (BMEP) in the cylinder – an effective indicator of engine performance – showed that peak output can be achieved at just 8,000 rpm with a relatively low 9.5:1 compression ratio.
This practically means that the MC4S engine should produce vast amounts of power working at a level that doesn't place significant load on pistons, piston rods, bearings and valve springs. The effectiveness of the combustion process can allow for a lean mixture, resulting in good fuel economy and equally low emissions.
Dan Gurney plans to build several different engines using this design principle. His patent refers to the twin cylinder engine that is illustrated in the patent drawings, as well as four, six and eight cylinder variations. He plans to have a twin-cylinder working prototype on his test bench by the end of 2015, so hopefully we will soon know if the revolution of the internal combustion engine is imminent or not; because, as much as we want to believe, it still sounds too good to be true. But that's how progress is made, by people who take on those challenges that everyone else considers to be impossible.
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