Can Dan Gurney’s Moment-Cancelling engine breathe new life into internal combustion?
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 formercompetitor Chuck Palmgren, believe that despite 120 years of development, the four-stroke engine hasn't been able to makesignificant advancements in addressing two fundamental problems: optimumcombustion and user-friendly operation.
"I'm notanti-electric automobiles," says 84 year-old Gurney. "The fact is that thereare 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 evenmore competitive with electric power for some of those decades."
Hispatented design stands out by incorporating a twin crankshaft configuration that we haven'tseen in the motorcycle industry for many years. Its roots reach as far back asthe 1910s, to Bugatti's airplane U-Engine. But in the motorcycling world its mostnotable early appearance would be in the Ariel Square Four from the 1930s, whileyounger generations probably remember Suzuki's RG500 and Kawasaki's KR250 and350 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 astructural problem in every internal combustion engine.
"Without specialbalancing systems, vibration and reciprocating engines go together," heexplains. "My experience is that things vibrate for a while, then fatigue andfall off or fall apart."
The MC4Sengine is a tandem twin – the two cylinders are positioned along the axis of theframe – with a different crankshaft for each cylinder. As the two shafts rotatein opposite directions, their moments balance each other out, thus eliminating theneed for balance shafts and making for a simpler structure with fewer movingparts.
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 balancinggear that has been removed. This design should benefit the bike's handling as themoment-cancelling nature of the engine promises a completely neutral feeling whenthe motorcycle tips into a corner.
But that'snot all. As we delve deeper into the patent description, things get even moreinteresting. Gurney ventures into the world of optimal combustion by designing the intake system with an oversquarecylinder (piston bore larger than its stroke) and a meticulously calculatedrelationship of the intake valve area to the bore area.
The intake port has a "doubletapered" cross section, as its diameter gets thinner in the middle section,forcing the flow to accelerate, before gradually expanding to meet the exactvalve seat size. Playing around with small variations in intake port diameterand inclination, as well as valve seat angles, results in what Gurney calls the "optimized taper configuration" and some astonishing output results.
The firstprototype 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 andfour valve heads. According to the simulations that Gurney has run, the MC4S enginewith a standard straight intake port will produce 141 hp (105 kW), while the output of the verysame 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 burningnormal pump fuel. According to the patent text, this is simply the result ofdelivering 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 – aneffective indicator of engine performance – showed that peak output can beachieved at just 8,000 rpm with a relatively low 9.5:1 compression ratio.
Thispractically means that the MC4S engine should produce vast amounts of power workingat a level that doesn't place significant load on pistons, piston rods,bearings and valve springs. The effectiveness of the combustion process canallow for a lean mixture, resulting in good fuel economy and equally lowemissions.
Dan Gurneyplans to build several different engines using this design principle. His patentrefers 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-cylinderworking prototype on his test bench by the end of 2015, so hopefully we willsoon know if the revolution of the internal combustion engine is imminent ornot; because, as much as we want to believe, it still sounds too good to betrue. But that's how progress is made, by people who take on those challenges thateveryone else considers to be impossible.