Car and Driver: Gurney in 2016! Racing Great Developing Counter-Rotating, Twin-Crank Two-Cylinder Engine

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From the February 2016 issue

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While poltroons, charlatans, earnest amateurs, and fuzzy idealists vie for the presidency, in Southern Cali­fornia, Dan Gurney drafts proposals for a ­better internal-combustion engine. No, it’s not 1964, and we’re no longer stumping to send Mr. ­Gurney to Washington. But the 84-year-old non­pareil racer-cum-inventor refuses to retire. His latest work is the patented design of an internal-combustion engine intended for production vehicles.

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With the pistons and the connecting rods rotated 90 degrees, the MC4S’s two cylinders drive individual crankshafts that rotate in opposite directions.

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Called the MC4S, for moment-canceling four-stroke, it’s intended to be smoother and more reliable than the internal-combustion status quo. The design prioritizes durability, efficiency, and simplicity above power, and yet the engine still achieves the kind of perform­ance you’d expect coming from a guy with 51 major racing vic­tories. Gurney proposes that the MC4S engine could be used in everything from helicopters to cars; a motorcycle is the obvious first application, though.

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The breakthrough feature is in the bottom of Gurney’s two-cylinder, twin-crankshaft engine. Counterweights attached to the cranks cancel primary shaking forces as usual. Rotating the cranks in opposite directions eliminates the undesirable gyroscopic moment (rotating force) that occurs when the entire engine is rapidly rolled for cornering, hence the moment-canceling name. While this benefit is a boon to motorcycles, it doesn’t apply to four-wheeled vehicles because their engines roll only a few degrees in corners.

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• Archived Feature: The Cannonball Baker Sea-to-Shining Sea Memorial Trophy Dash-
• Everything You Ever Wanted to Know About Pistons-
• The 10 Most Unusual Engines of All Time-

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The engine displaces 110 cubic inches, or 1800 cubic centi­meters, with a broad 5.0-inch bore and a short 2.8-inch stroke. For the sake of durability, the average piston speed will be limited to 4200 feet per minute at 9000 rpm. Gurney also suggests that the patent could be adapted to four-, six-, and eight-cylinder designs.

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Simulations predict the two-cylinder would make more than 250 horsepower, surprising Gurney’s team. “We didn’t think the numbers would be as large, but the same simulations have worked on our other engines within 2 percent,” he says.

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Gurney plans to build five prototypes, the first of which should be running on a test stand by July. If the engine lives up to its theoretical potential, Gurney hopes to license the design to a manufacturer. “We certainly have no idea how to produce anything at a reasonable price,” he admits.

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Angle in the Dangle

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The counter-rotating crankshafts get the headlines, but the MC4S’s impressive power is a product of its cylinder-head design. Gurney studied more than 200 valve-configuration variations to find the best arrangement. The intake ports taper to accelerate airflow, as is common in racing and high-performance engines. An optimum amount of squish—the inward movement of the air-fuel mixture toward the center of the chamber as the piston approaches top-dead center—improves combustion. Cam phasers tweak the timing of valve events to balance low-end pull with top-end vigor. Computer simulation suggests that the idealized cylinder head leads to a 15-percent increase in the amount of airflow versus a conventional head. With that design, the engine should be good for 262 horsepower. The simulation predicts an output of 189 horsepower with a conventional head.

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History Lesson

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Then editor-in-chief David E. Davis Jr. launched the campaign to elect Dan Gurney president of the United States with his July 1964 column. While popular with our people, Gurney never appeared on any ballots. He was only 33 years old at the time, and thus ineligible to be president.

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