The Bentayga’s product manager, Peter Guest, said: “We would only do this when it was right. It had to be the right car and the right engine.”
Installing a potentially coarse diesel in a Bentley is a risk, even if this powerplant’s instant low-rev torque provides the stream of effortless thrust required. The brief, said Guest, was to deliver the Bentley driving experience with the trademark combination of performance and luxury, and no compromise in refinement. It also had to be “the fastest diesel SUV in the world”.
Bentley powertrain development boss Paul Williams said the three technologies that have enabled the firm to offer a diesel worthy of the brand are the engine’s triple-charging system, the 48V supplementary electrical system used to power the electric supercharger, and a sophisticated exhaust cleansing system.
The triple-charging system, previously seen in the Audi SQ7, which uses the same engine, provides boost at low revs from the near-instantly reacting supercharger.
This so-called e-booster also primes the first of two twin-scroll turbochargers. This first turbo amplifies midrange thrust, then a second twin-scroll turbo provides extra shove at mid to high revs when the e-booster is dormant.
The effectiveness of the e-booster is heightened by a valve shut-off system, whereby an exhaust valve disengages to provide faster combustion pressure build-up. The exhaust gases are dealt with by using a selective catalytic reduction system, an AdBlue urea fuel supplement and an additional catalyst. Williams said the system is “state of the art and meets all current and future legislation”.
The Bentayga has been acoustically engineered for the V8 diesel from the start and changes to the rest of the car are minor. The exhaust system has been modified — without artificial enhancement — and there are minor tuning changes to the suspension to cater for the weight redistribution caused by the 23-litre AdBlue tank.
The V8 diesel engine itself weighs only 3kg more than the W12. Black radiator mesh, ‘twin quad’ tailpipes and badges identify the Bentayga Diesel.
Electric supercharger requires 48V to power its 7kW motor, enabling it to spin from idle to 70,000rpm in only 250 milliseconds. The result is maximum torque of 664lb ft from only 1000rpm and superb motorway on-ramp acceleration.
The electric supercharger (on the bottom right) feeds the cylinders at low revs for near-instant torque. One exhaust valve is closed to intensify the boost, while the exhaust gases prime the second turbo (in the centre). All three chargers feed all eight cylinders and the turbos are twin-scroll.
Three turbos are located in the vee of the engine and the electric supercharger is remotely mounted. A sliding cam deactivates one exhaust valve when the supercharger operates. The sub-assembly is part of the cooling system.