Cagiva-Ferrari Secrets Revealed

CAGIVA-FERRARI SECRETS REVEALED

ROUNDUP

CAGIVA'S CLAUDIO CAS tiglioni recently crowed to the press that the company’s new four-cylinder bike, developed in conjunction with Ferrari, would have a feature of such obvious merit that designers of conventional transverse-Fours would kick themselves for not thinking of it (see Roundup, January). Now it can be told.

The feature-a reversed head with forward-facing intakes and rear exhausts-is less significant than other innovations in the design. Forward-facing intakes simplify the delivery of ram air, but don’t increase airbox ram pressure over good rear-intake designs like Kawasaki’s.

Truly significant in this Italian design is its radial-valve construction and, possibly, staggered-cylinder architecture. Presently at 920cc, a 750cc-version is also planned and will be the first Cagiva-Ferrari released, facilitating Cagiva’s entry into World Superbike racing.

The quest for power, in Superbike as in F-l cars, seeks higher revs. To rev higher without excessive stress on con-rods and pistons, the stroke must be made shorter

and the bore bigger. This combination creates wide, thin combustion chambers that burn more slowly than do those of smaller-bore designs. The result is power loss as combustion takes an excess share of the engine cycle.

Present Superbike engines all have pent-roof, four-valve combustion chambers (save for Yamaha, with its five valves), with a central sparkplug. Seen from the end, such a chamber is a flattened triangle, which concentrates the fuel-air charge near the sparkplug. Viewed from front or back, though, it’s a low, wide rectangle. But a radial-valve chamber substitutes a pyramid-form chamber for the pent-roof; its valvestems protrude in four directions instead of only two.

Look at a radial-valve chamber from any side and it is a flattened triangle, with the sparkplug at its apex. Such a chamber offers improved charge concentration under the plug, a shorter burn time, and higher combustion efficiency.

Cagiva’s cylinder head is a Ferrari design. While the current World Superbike champiKawasaki, has a 72mm bore

and 46mm stroke for a moderate bore/stroke ratio of 1.57, Ferrari and other Formula One engine builders are working with higher bore/stroke ratios of 1.8 or more. With such a bore/stroke ratio, a 750 Four would then have dimensions of 75.3 x 42mm. This short stroke, combined with friction-limiting design practice, could rev to 14,000 rpm at a streetable stress level, or to 17,000 as a race engine. At currently achievable levels of breathing, this kind of rev-ability would handily allow the street 920 engine to make the 130 horsepower claimed for it. It would also allow a racing 750 version to make 170 horsepower.

There is, of course, a long history of smallish Italian horses, and much can be lost between the first strokes of the designer’s pen and the final hardware. Despite this, the Cagiva-Ferrari has specific design advantages over its competition that could back up the figures. An improved combustion chamber is just what current Fours need most-to allow a shorter stroke and higher revs.

One Cagiva prototype contains a second significant feature: staggered cylinders, which allow a big-bore design narrower than smaller-bore current inlines. It’s uncertain that this feature will be used and the degree of stagger is not known, but such a narrowangle “V-Four” could be served by two cams (through angled rockers) instead of the usual four.

Does the world need another four-cylinder bike? Cagiva and Ferrari are attempting to show that clever engineering can put new life into the venerable transverse-Four concept.

Though this concept is today thought of as Japanese, we must remember that the granddaddy of all transverse-Fours was itself Italian-the 1923 wo k of engineers Gianini and I mor, which became the endless copied Gilera Four. —Kevin Cameron