Following the positive reception to the Paso after the Milan Show of 1985, the Castiglionis were enthusiastic to develop a more modern, four-valve engine. Massimo Bordi was given the task of developing this new engine. Bordi was an excellent choice, having completed his degree in mechanical engineering with a thesis on a four-valve cylinder head with desmodromically actuated valves.

Over a period of six months many designs were investigated, including regular valve spring four-valve heads, heads with five and even six valves, and desmodromic four-valve heads.

The English firm Cosworth was consulted regarding the design of a four-valve cylinder head, but they wanted nothing to do with desmodromics. Cosworth was the partnership of Mike Costin and Keith Duckworth and they had created one of the most successful Formula One car engines ever in the Ford DFV V8. However, their brief flirtation with desmodromics had not been successful. As the Castiglionis wanted the new engine to be desmodromic, Bordi had to do much of the development himself.

As with Taglioni’s first design, the Gran Sport, the new engine wasn’t to be compromised by the limitations of production engineering. From the outset the motor was designed for maximum performance.

Ducati 851

Water-cooling enabled full advantage to be made of four-valve heads with a narrower included valve angle. Previous experimentation with four-valve heads on the air cooled 500 twin in 1971-73 had yielded little benefit because it was impossible to get a shallow enough combustion chamber. This new cylinder head was closely modelled on the Cosworth FVA Formula Two car engine with an included valve angle of 40º, and effectively was a full race system to start with.

The desmodromic layout used two belt-driven overhead camshafts per cylinder. These four lobed camshafts slipped through tunnels in the heads, supported by ball bearings on the right side, and bushings on the left. Two lobes opened the inlet valves through straight rockers, while the other two closed the valves with “L” shaped rockers.

Ducati 851

Using modified Pantah crankcases, but with more widely spaced cylinder studs, the prototype engine shared the dimensions of the 750F1 at 88 x 61.5mm, giving 748cc. This enabled it to be run in the World Endurance Championship, but with the air-cooled Pantah being raced concurrently in 851cc form, it was obvious that development of the new engine would include a larger capacity. The prototype was the first Ducati to use open-loop computerised electronic fuel injection.

Derived from experience in Ferrari Formula One racing cars, the Weber-Marelli IAW fuel injection system used sensors to monitor coolant temperature, engine revs, throttle position, air temperature and barometric pressure. These sensors were common components used on a range of Lancia and Fiat cars, and were sometimes of dubious quality. The computer memory contained a number of maps, and depending on the information from the sensors, plotted the timing of the two injectors along with the ignition advance.

Ducati 851

Five months after the initial drawings appeared, an engine had been tested and installed in a modified 750F1 frame and a few days later the bike was racing at the Paul Ricard circuit in the south of France at the Bol d’Or 24 Hour endurance race. Ridden by Marco Lucchinelli, Juan Garriga, and Virginio Ferrari, after fifteen hours the new 748 was in seventh place before retiring with a broken con-rod.

The next meeting for the new motorcycle was at the Daytona Battle of the Twins race in March 1987. Now in 851cc form, it produced a claimed 120bhp at 11,500 rpm at the rear wheel, and Marco Lucchinelli easily won the twins race. 1988 was the first year of the World Superbike Championship, and Ducati needed to build 200 bikes in order for the 851 to be homologated for that series. The 851 could race because the regulations allowed for 1000cc two cylinder bikes to compete against 750cc fours.

Ducati 851

Three versions were offered to prospective customers, comprising twenty Lucchinelli Replicas, 200 851 Superbikes, and 300 851 Stradas. The Stradas were the tricolore models, and they were largely hand built because full scale production hadn’t yet been implemented. The all red Lucchinelli Replica was 888cc, just like the factory racer, and with its 11.2:1 compression, claimed power (at the crankshaft) was 130bhp at 10,500 rpm.

Most who wanted to race an 851 didn’t have access to the Lucchinelli replica, but could purchase an 851 Superbike. Purely a homologation special, these were an unusual mixture of street and racing bike. In red, white, and green, with a silver frame, they came with Michelin racing slicks mounted on magnesium 3.50×17 and 5.50×17 Marvic wheels, electric starter, a sidestand, and a headlight and taillight. The engine was 851cc and with a modest 10.6:1 compression ratio, claimed power was 120bhp at 10,000 rpm, at the crankshaft.

The brakes were two 280mm fully floating Brembo discs on the front, and a 260mm on the rear, with street type Brembo P4.32B and P2.T08N calipers. In other respects the 851 Superbike was the same as the Lucchinelli Replica, and also had the braced aluminium swingarm. Wheelbase was up slightly to 1460mm (57.5 inches) and claimed weight was 165kg (364lb) dry, but this was very optimistic. “Cycle World”, testing an 851 Superbike in April 1988, weighed their bike at 417lb (189kg) dry, and 445lb (202kg) wet. Too much for a racing bike. Still, they managed a top speed of 154mph (249km/h).

Ducati 851

Alongside the 851 Superbike was the 851 Strada. Using the same frame (without the reinforced swingarm) and similar bodywork (with Paso style mirrors), the Strada differed in the use of the 16 inch Marvic/Akront composite wheels, and a detuned engine. With slightly less compression than the 851 Superbike at 10.4:1, the Strada produced a claimed 102bhp at 9000 rpm at the crankshaft.

Another difference between the two models was in the use of the Paso exhaust system and 16-inch Marvic composite wheels, as fitted to the 750 Montjuich and 750 Santa Monica. The brakes were identical to the 851 Superbike and claimed dry weight was 185kg (408lb).

The Stradas were criticised for uncertain handling due to the 16-inch wheels and had some problems with fuel vapourisation on hot days. Because they were very expensive, they weren’t a particularly successful model, and they were sold at discount prices during 1989.

Their performance wasn’t as spectacular as it was claimed to be, but it was probably the idiosyncratic handling characteristics that condemned it. However, these first available street versions of the ottovalvole featured many individual and hand crafted pieces, like the rear shock absorber rocker linkage, and used high quality components such as fully floating discs front and rear and braided steel brake lines.

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