No Prancing Horsepower For Cagiva
NO PRANCING HORSEPOWER FOR CAGIVA
Now WF’RE CONFUSED. First we were told Cagiva’s Ferrari-designed 750cc Four would have forward-facing intakes, radial four-valve combustion chambers, even staggered cylinders like Audi’s narrow-angle V-four. Now, the reality seems to be entirely different.
The engine is not by Ferrari, according to the grapevine. Intakes are at the rear in conventional fashion, with four cylinders in line rather than staggered. With the two cams, rumored to be centrally driven by chain, as closely spaced as they are. there’s little room for radially disposed valves (as in Honda’s off-road Singles).
This engine is quite conventional except it is very short from front-to-back. The more centralized a motorcycle’s mass is made, the quicker it can change direction-just as it is easier to turn a corner carrying a 24-pound cannon ball than it is with a 24-pound ladder. The shorter the engine, the longer the swingarm can be. The longer the swingarm, the less drivechain pull can affect rear-suspension action. This is trivial on the street, but crucial on the track. Note the tremendous swingarm length on Honda’s NSR racebikes.
In traditional Japanese fashion, engine accessories are removed from the crank ends, stowed either atop the gearbox or ahead of the engine. The result is a narrowed, compact powerplant. This engine was created by someone more concerned with design integration than with generating the last possible horsepower.
The photo shows the engine with its cylinders vertical, but when mounted in the rumored twin-beam aluminum chassis, they incline steeply forward in Yamaha FZR/YZF fashion. This in turn puts the fuel injection trumpets in a near-vertical position.
Why, after all the talk of radical solutions, is the revealed engine relatively conventional? Our grapevine tells us that the Ferrari connection has been a disappointment for Cagiva. Ferrari, too long out of contention for the Formula One championship, has been forced to gamble lately on novel ideas. Among these are the radial-four-valve, conicalcam concept of the late Austrian engineer Ludwig Apfelbeck, and the five-valve concept associated with Yamaha. The Ferrari-Cagiva prototypes, the vine says, made poor power, and Cagiva’s capable Ingegnere Massimo Bordi became disillusioned and decided to go it alone.
Other makers-notably BMWhave tested Apfelbeck prototypes, yet none is now in production. Why? As valve included angle approaches zero in the process of creating an ever-more-compact combustion space, the difference between radial-four-valve and pent-roof heads disappears.
And what about five valves? Yamaha built a few five-valve auto-racing engines, but has reverted (without saying it too loudly) to four valves in the most recent designs. The fourvalve chamber is the best compromise between compactness, simplicity and valve area.
Bordi may have rejected novelty in favor of practicality.
Kevin Cameron
