BMW V12

Figure 1
At the end of 2002 BMW presented an entirely new V12 for the 760 i and 760 iL. Compared to the former V12, the cylinder spacing has been increased from 91 to 98 mm to enable a bigger bore. It has been enlarged from 85 to 89 mm while the stroke is only augmented from 79 to 80 mm. The cubic capacity is thus established at 5972 cc against 5379 cc for the final version of the preceding engine. We immediately assumed that the new engine was designed for a further increase in cubic capacity. That was obvious since Alpina already obtained 6 liters on the B12 with the previous block by a bore of 86.4 mm and thanks to a special crankshaft providing 85 mm of stroke. Then on January 7.03 the characteristics of the news Rolls-Royce Phantom equipped with the same basic engine block have been revealed: 92 x 84.6 mm for 6.749 liters.

The iron coated pistons slide directly in the uncoated bores, which are hardened by a specific process using silicon crystals (Fig. 2). A fundamental difference springs from the fact that the new cylinder block, although in aluminum alloy also, is of the open deck type whereas its predecessor was of the closed deck kind.

Figure 2

The main bearings are in cast iron and they are reinforced by additional oblique screws. The rods have a 140 mm distance between centers for a liberal length/stroke ratio of 1.75. They are fractured along a 30° angle, which makes it possible to set crank pins of a larger diameter (Fig. 3).

The cylinder heads include henceforth 4 valves per cylinder and they are provided with the revolutionary device Valvetronic (presented in a separate file) which adjust the engine's output by varying the opening durations and lift of the valves between 0.2 mm at idle and 9.8 mm at full load (Fig 4).