It is a sight to shock an engineer from a high-volume engine plant: a total of 16 engine builders individually assembling 6.75-L V8 engines, each taking 26 man-hours to do so.
But that is the scene at Bentley’s Crewe (England) engine shop, where the powertrains for the automaker’s new Mulsanne sedan are being built. First deliveries of the car will be in late summer.
Its new lightweight crankshaft, held in place by five bearers, is lowered into the crankcase by hand. Also installed by hand are the lightweight pistons and the spherical end-caps of the pushrod assemblies.
Weight savings, compared to the previous engine, include 13.5 kg (30 lb) in the crank assembly. The pistons are 140 g (4.94 oz) lighter, and the con-rods are 80 g (2.8 oz) lighter. Engine balancing uses weights of less than 1 g (0.04 oz). The engine weighs 320 kg (705 lb) fully dressed.
In all, the engine’s 700 parts (300 of them new or significantly re-engineered for the Mulsanne) receive similar attention, and when it is all complete and shining, the assembler’s name is attached via a small but very significant plate.
“We never release an engine to our colleagues in the main build hall until we are literally prepared to put our name on it,” said Phil Cooper, Bentley’s Senior Production Manager, Engine Build Workshop.
The basic configuration of the engine was introduced in 1959 on the Bentley S2 Continental, when it generated 149 kW (200 hp) at 4000 rpm. But this definitely does not mean that the V8 is now some archaic piece of machinery. Over the following decades, it has been improved, enhanced, and made ever more efficient to power the Turbo R, original Mulsanne, Brooklands, Azure, and Arnage models.
Now, having been “completely re-engineered,” according to a company statement, it provides 1050 N·m (774 lb·ft) from 1750 rpm with a power output of 377 kW (506 hp) at 4200 rpm, figures achieved with the support of twin Mitsubishi turbochargers.
Bentley has a stated aim of drastically reducing the fuel consumption and CO² emissions of its models through the application of advanced technology. For the big V8, this includes cam phasing and variable-displacement systems, which are responsible for improving both by about 15%.
The variable-displacement application sees closure of the valves of four cylinders to achieve optimum potential fuel consumption during cruise.
A balancing machine is used to check that all spinning components, as Bentley phrases it, are tested and, when necessary, rebalanced using very small washers. One quality requirement is to achieve virtually zero vibration at engine idle.
Every Mulsanne engine undergoes an 80-min hot test cycle including idle to maximum revs, with the engine subjected to simulated real-world driving loads.
The big V8 drives through a ZF eight-speed automatic transmission developed specifically for the Mulsanne. It is the first time Bentley has used an eight-speeder.
Performance figures for the Mulsanne include a 0-100 km/h (0 to 62 mph) time of 5.3 s.