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BMW Valvetronic (2)

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BMW Valvetronic (2)

by François Dovat

Hence the inlet valves lift changes continuously from about zero to 9.7 mm (4 cylinders 1.8) and the engine output is adjusted in the most logical way. Moreover, under partial load the friction losses in the valvetrain are decreased. The system presents however the disadvantage of a total mass increased by that of the additional lever, so that stronger valve springs are necessary. As a result the red line is set to 6500 t/mn.

The 4.4 liters V8 (opposite) and the V12 also profit from this revolution. It should be noted that the 4 cylinders (above) is provided with Lanchester balance shafts.

The bearing caps of the new engines are integrated in a bedplate, just like in most racing engines and marine diesels with high pressure turbocharging. Each main bearing is flanked by 4 studs. This solution offers best structural rigidity.

The light alloy engine block is of the open deck type with an integral timing chain case.

Additionally the V8s are fitted with continuously variable length inlet runners adjusted according to the revs in order to profit from the harmonic vibrations of the airstreams generated by cyclic closings and openings of the valves. The charging is thus optimal on the whole rev range, especially since no throttle plate causes turbulence.

A poly-V belt ensures the drive of all the accessories.

The performances of these new engines are clearly improved. The 4.4 liters V8 power is increased from 286 to 333 hp (ECE) whereas their consumption is reduced by 10 to 14 %. See also our file about the new V12 on which the Valvetronic is used together with direct injection, and the one about variable length intake runners.

(© François Dovat)

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