The Benelli 750 Sei was the first production motorcycle with a six-cylinder engine. Benelli unveiled it in Modena, Italy, on October 27, 1972. Its engine had an unusual family tree, too. Benelli built it by adding two cylinders to its own four-cylinder 500, which was a near-copy of the Honda CB500.

The result was an Italian challenger to Japan’s superbikes, built on a Japanese layout. It was also expensive, slow to reach showrooms and never a big seller.

Still, it held the six-cylinder field alone for several years. Here is how the bike came together, what it could do and how many Benelli built.

De Tomaso’s plan for the Benelli 750 Sei

Alejandro de Tomaso, the carmaker behind the Pantera, bought Benelli in 1971. According to Old Bike Australasia, he announced that he was “declaring war” on the Japanese factories. The 750 Sei was his headline weapon.

Silodrome says de Tomaso wanted a two-wheeled version of his Pantera. In addition, he aimed to build the first six-cylinder production motorcycle. Carrozzeria Ghia styled the angular bodywork, the same site notes.

The unveiling at the Grand Canal Hotel in Modena came with typical de Tomaso fanfare, Old Bike reports. However, production bikes reached showrooms almost two years later, around 1974. Bikesales likewise dates the start of production to mid-1974.

How Benelli turned a four into a six

The Sei’s engine started with the Benelli 500 Quattro. That four-cylinder was itself a near-copy of the Honda CB500, Old Bike says. To make the six, Benelli added one cylinder to each end of the 500’s crankshaft.

The proof is in the measurements. The 750 Sei’s bore and stroke of 56 x 50.6 mm match the Honda’s exactly, according to both Old Bike and Bikesales. Honda didn’t supply the engines, though. Benelli built its own copy and then stretched it.

Even so, Benelli did make some changes. For example, the six breathed through three Dell’Orto VHB 24 mm carburetors, while the CB500 used four, according to the Benelli Sei reference entry. That entry also notes squared-off cylinder fins to set the engine apart.

The layout itself was simple. Shannons describes the 750 Sei as a triple-carburetor, single-overhead-cam, 12-valve design. As for the name, sei is simply Italian for six.

Benelli also moved the alternator and starter motor behind the cylinders. By contrast, the Honda carried its alternator on the end of the crankshaft, Old Bike explains. Finally, the 750 wore six separate exhaust pipes, which produced what the magazine calls a “raspy shriek.”

What the Benelli 750 Sei could do

The power figures were modest for a six. Early road tests found about 75 hp, according to Old Bike. Meanwhile, the reference entry lists 76 bhp at 9,000 rpm, and Bikesales quotes 71 hp at 8,500 rpm.

Most road tests recorded a top speed of around 190 km/h, or about 118 mph, Bikesales says. But the price was the bigger problem.

The Sei cost almost double the Honda CB750 and the Kawasaki Z1, Old Bike reports. As a result, buyers who wanted a fast 1970s superbike had cheaper Japanese choices.

How many Benelli built

Benelli’s official figures put 750 Sei output at 3,200 bikes from 1974 to 1977, according to Old Bike. Bikesales breaks that down by year: 293 in 1974, 1,479 in 1975, 1,145 in 1976 and 283 in 1977.

Those yearly figures add up to the same 3,200 total. The reference entry splits the years differently and runs its table into 1978. Even so, it also arrives at 3,200 bikes. Silodrome simply says that over 3,000 were made.

The 900 Sei and the Honda CBX

For 1978, Benelli announced a bigger 900 Sei. It used a 60 mm bore and 53.4 mm stroke for 906 cc, Old Bike says. The 750’s six separate pipes gave way to a twin-muffler system.

Until then, the Benelli had been the only six-cylinder production motorcycle, the reference entry notes. By 1978, though, the Sei had company. Honda launched its own six, the 1,047cc CBX, in 1978, according to Shannons. That bike went on sale in late 1978. Moreover, the CBX had four valves per cylinder and double overhead camshafts. Next to it, and to Kawasaki’s water-cooled Z1300, Old Bike calls the Benelli underpowered.

The Sei carried on regardless. Bikesales says the 900 Sei stayed in production until 1988. Shannons, for its part, still credits Benelli with the world’s first production six, launched in 1972.

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This article was created with the help of AI and was reviewed and edited by Fast Lane Only editors before publication.