Ferrari Berlinetta Boxer Drivetrain

Chosen for its compactness and natural harmony, the 'Flat' 12-cylinder engine, often referred to as a 'boxer' for the way its horizontally-opoosed pistons mimic the actions of sparring pugilists, is a marvel of efficient design. The 365 GT4/BB appeared in 1973 with a 4390cc block cast in silumin, an aluminum alloy. The bore was 81mm and the stroke 71mm. The four overhead camshafts were driven by toothed belts rather than chains. The camshafts actuated two valves per cylinder. At the centre of the engine lies a seven main bearing crankshaft milled with the unsurpassed precision necessary to a boxer engine. A very safe compression ratio of 8.8:1 was engineered. This combination gave 360bhp at 7500rpm, and 311lb-ft of torque at 4500rpm. The 365 GT4 had Weber carburettors fed by twin pumps from a 46 gallon reservoir. Ignition was Marelli Dinoflex and lubrication was via wet sump. Aided by fans, a single front-mounted radiator provided cooling.

512 BB

The powerplant of the 1976-81 512 BB was enlarged to 4942cc by increasing the bore to 82mm and the stroke to 78mm, and raising compression to 9.2:1. With squarer cylinders the new engine achieved a conservative 340bhp and 331lb-ft at lower engine speeds than its predecessor. Dry sump lubrication was also installed.

512 BBi

In its final revision, the 512 BBi's engine saw a Bosch K-Jetronic fuel injection system replacing carburretion, making it more tractable and fuel efficient in a greater variety of conditions. The 512 BBi has 340bhp at 6000rpm and 333lb-ft at 4600rpm.

Transmission

As part of the effort to perfect a midship Flat-12 design on the first attempt, Ferrari placed the five-speed transmission directly below and slightly offset to the rear of the longitudinally aligned engine. Drive is transferred from the engine via strong chains, and through a single-plate hydraulic clutch in the 365 GT4/BB, and a dual-plate hydraulic clutch in the 512 BB and 512 BBi.

The all-syncromesh transmission consists of five forward and one reverse close ratio gears, fourth being an underdrive and fifth an overdrive. The 512 BB and 512 BBi have slightly shorter gearing than the 365 GT4/BB, which helps account for their lower top speed and more consistent acceleration.

The limited-slip differential employs a helical spur gear crown wheel and pinion. The 512 BB/i have a slightly taller final drive than the 365 GT4/BB.

As a Gran Turismo, the Boxer was never geared for ultimate velocity, although it could exceed 170mph without modification. Rather, the transmission of the Boxer was designed for enjoyable interaction between human and machine. It provides for extremely spirited acceleration, and safe passing in any gear, with more than enough speed for the race track or the road.