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The new BMW V12

by François Dovat

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).

Moreover the engine has a common rail direct injection system. The vaporization of the gasoline directly in the combustion chambers provides the advantage of a cooling of the charge which improves the cylinders filling (Fig. 5).

Two chains drive the 4 camshafts via "Double Vanos" (in fact quadruple on the V engines) timing variators and a third chain drives the oil pump (Fig. 6).

The long magnesium intake runners improve the cylinder charging in the medium rev range, apparently around 4000 rpm. (Fig. 7 and 8).

The oil sump contains 8.5 liters and oil changes may be spaced up to 40 000 km according to the conditions of use and indications of the inboard computer.

While the former V12 weighed 240 kg in its first version (5 liters), the new beast weights 280 kg. It doesn't produce less than 445 hp (ECE) at 6000 rpm (10.9 bars of mean effective pressure) and 600 Nm at 4000 rpm (12.5 bars of m.e.p.). Its torque back up calculated this way is thus 12.5/10.9, that is to say 1.15 or 15%.

However, by letting it rev up to the 6500 rpm redline one will obtain if necessary (!) a torque back up of 33%... Such a power curve is enough to catapult the 2.09 tons of the 760i to 200 km/h in 17 seconds, 100 km/h being reached after 5.5 seconds. In conjunction with an axle ratio of 3.15 and tires of 245/50R18, the ZF 6HP26 automatic transmission without direct drive gives 64 km/h per 1000 rpm in 6th speed. Its ratios are 4.17 – 2.34 – 1.52 – 1.14 – 0.87 – 0.69. Standardized fuel consumption is indicated at 19.5 l/100km in city driving, 9.2 highway and 13.4 average. The longer version 760iL being 160 kg heavier, it burns 1 l/100km more gas in city driving. With its high compression ratio of 11.3 :1 the over-mighty V12 prefers the 98 ROZ high octane gasoline, but it can, if required, also live with 91 ROZ gas.

The announced performances are even higher than those of the former Alpina B12 6.0 of 430 hp, except that the maximum speed is limited at 250 km/h whereas the B12 could reach 291 km/h. Bah, rounded off 290 km/h (180 mph) would have been enough I guess… and undoubtedly 250 km/h also is.

But just in case you need more power and speed, the tuner Hamann has presented at the 2003 Geneva Motor Show an upgraded version. Extract from their press release:

"The HAMANN capacity increase to 6,931 cm3, which will be available from Summer 2003, is made via the installation of a special crankshaft, the boring up of the cylinders and the fitting of bigger forged pistons. In addition the two cylinder-heads of the V12 four valve engine get machined and sport camshafts are installed. The tune-up also contains modifications on the air induction, the installation of a stainless steel made high performance exhaust system including special manifolds and metal-bed catalysts and a recalibrated ECU which perfectly coordinates all components. Of course the modified ECU also eliminates the standard electronic speed limit of 250 km/h.

The conversion to HAMANN HM 7.0 specification improves maximum power from standard 445 hp / 327 kW to 510 hp / 375 kW at 6,000 rpm. Simultaneously the maximum torque grows from 600 Nm to 728 Nm at 4,200 revs. Accordingly the road performances of the 760i/Li are improved: The tuned luxury limousine only takes 5.0 seconds from 0 – 100 km/h. Maximum speed is 311 km/h."

Hamann politely refused to divulge the bore and stroke.

(© François Dovat)

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Idée & conception © 1999-2011 van Damme Stéphane.

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