Ducati’s New Superquadro Mono 660 Single

[Admin]

One piston, one rod, two balancers, and a desmo head—Ducati’s 659cc Superquadro Mono engine creates a claimed 77 hp. (Ducati/)

Many industries are now motivating buyers with lower prices, and a trusted technique is reduced parts counts. From fewer stages in multimillion-dollar large fan engines for airliners, to the proliferation of twin-cylinder motorcycles in place of traditional fours, this is a clear trend.

Until the coming of Ducati’s recent V-4 engines, the company focus was on meeting or exceeding four-cylinder performance with light, high-revving 90-degree V-twins. Doesn’t it now make sense for Ducati, confronted by the parallel-twin revolution, to use its established less-is-more technology to build high-performance singles?

The key to performance for Ducati’s V-twins was high rpm, made possible by reducing vibration. Ducati quelled the vibration that had kept traditional twins from operating at such high revs by orienting the cylinders at 90 degrees to each other, making it possible to achieve full primary balance.

The Superquadro’s design begins with the least expensive technology: that which is already paid for. That is the cylinder head from its 1299 Panigale, placed atop a new, compact and short front-to-back, vertically split die-cast single-cylinder crankcase. Its name means oversquare, and at 116mm bore by 62.4mm stroke, for a bore/stroke ratio of 1.86 it is more oversquare than any engine in MotoGP (where the limit is set at 1.67). The separate cylinder liner is hard-plated aluminum, as it is in the Superleggera.

A hard-plated aluminum cylinder is used in the Superquadro. (Ducati/)

Engine side covers are of cast magnesium, which has only two-thirds the density of aluminum.

People speak of “oversquare” as if it were a mystic essence, but in fact all a big bore does is make room for valves big enough to fill its cylinder well in the ultrashort times allowed by high rpm. A byproduct of this is a short stroke that, at a given rpm, reduces piston acceleration and the inertia loads on bearings.

By now the reader may object, “But didn’t Ing. Massimo Bordi already design a balanced high-performance Ducati single—the engine of the 1993 Supermono?”

Side covers are magnesium. (Ducati/)

That engine was indeed given complete primary balance by providing a second connecting rod, pulling and pushing a piston-simulating weight that oscillated on a lever. But that second rod occupied space that made the engine less compact. Today’s engines in many cases save even more development money by being usable in multiple applications. That requires them to be compact, providing options useful in positioning them in more than one variety of motorcycle.

For that reason, primary balance is achieved in Superquadro via a pair of gear-driven crank-speed shafts—one ahead of the crank, one behind—carrying eccentric weights. In the words of the press release, this “allows the first-order inertia forces to be completely balanced.”

The pumps for liquid coolant and oil are driven from these ball-bearing balance shafts. As in many race engines, an oversized scavenge pump also pulls crankcase pressure down to a partial vacuum.

The crankcase is split vertically on Ducati’s Superquadro Mono. (Ducati/)

Claimed power measured on an engine dynamometer is 77.5 hp at 9,750 rpm, with torque peaking at 46 lb.-ft. at 8,000, giving “linear, accessible power delivery.” With the optional Termignoni exhaust system, the numbers become 85 hp at 9,500 rpm, with 49 lb.-ft. of torque.

This is made possible by use of the same valve diameters as in the 1299: 46.8mm titanium intakes and 38.2mm steel exhausts. The usual desmodromic mechanism in the head (opening and closing the valves by cam-driven levers—there are no valve springs) provides “extreme levels of valve lift.” Valve lift is not stated.

The tremendous 116mm piston (4.57 inches—bigger than that of a big-block Chevy) is very short; little more than a disc to carry the rings, braced under its crown by the usual four crisscrossing beams, with skirts of minimal height to guide it in the cylinder bore. We must assume there are oil jets to cool such a large piston, but they are not mentioned in the release.

Nearly eclipsed by the 116mm piston, the fracture-split connecting rod is ultrashort. (Ducati/)

The fracture-split steel connecting rod will look out of proportion to you because it’s so short, yet its big-end is nearly an inch wide.  This is because con-rod length is proportioned to the stroke (which is short) while bearing area must be proportioned to the applied load. Rods in the 1299 are 110mm long for a shortish rod ratio of 1.81 (110/60.8). Ducati usually chooses rod ratios in the range of 2.0 to 2.2, but it needed to reduce the external dimensions of the 1299 engine.

Applied load? If a peak combustion pressure of 1,200 psi is achieved, peak compressive force on the con-rod peaks at 20,000 pounds, or 10 tons. And that, dearly beloved, is why the con-rod’s big-end is so wide—to provide the necessary area of plain bearing to carry that load. The crankshaft also spins on plain main bearings—introduced on Supermono by Bordi who originally intended to apply to future twins. They finally arrived in the Panigale.

The crankshaft runs on plain bearings, just like the 1299 Panigale. (Ducati/)

How well does this engine breathe and burn? The arithmetic tells us it represents a pullback of about 17 percent from 1299-level performance, probably resulting from some reduction of compression ratio (it was 12.6:1 in the 1299) and maybe from valve timing changes. Although, in the latter case, the presence of deep valve clearance cuts in the piston crown suggest there is still significant valve lift at TDC, end of exhaust stroke. Compare with the relatively smooth piston crowns of the previous-generation Diavel, which has very little valve overlap. For that reason Diavel engineers have referred to it as “the 11-degree.”

This power and torque pullback is necessary: A large-displacement engine has oomph a single lacks, making some torque-broadening compromise useful. This is confirmed by the press release, which says first gear (of six) is “strategically long” to maximize acceleration from slow corners. Optional Ducati Quick-Shift up-and-down is available.

Superquadro’s DOHC are driven by chain from crank to a central combined sprocket and gear at the top, from which a gear on each cam takes the drive. The multiplate clutch is of slipper/assist type to both lighten lever pull and prevent dragging/hopping of the back tire by the compression braking of that giant piston (could also be a cogent reason to reduce compression ratio somewhat!).

A traditional concern of Ducati owners has been short valve-clearance adjustment intervals. In Superquadro valve-clearance check is set at 18,000 miles, like so many of Ducati’s other models now.

The single oval-section throttle body has the area of a 62mm (2.44 inches) round hole, with a single under-the-butterfly injector. Operation is throttle-by-wire.

An oval-section throttle body of 62mm equivalent round diameter feeds the Superquadro Mono. (Ducati/)

Ducati has also said it will build motocross bikes, but whether 250 or 450 is not revealed. Might Superquadro be a challenger in Dakar-style events? Singles have always offered advantages in off-road operation. Who can say? On the street, Superquadro’s acceleration will compare favorably with that of recent light/middleweight twins, and its simplicity can offer reduced weight. The compactness of its design, combined with the ability to change engine character either through electronics or via valve timing and intake/exhaust changes, will allow it to serve in multiple applications.

Singles lovers, arise!

View the full article