Turbocompounding seems to defeat the laws of physics by creating energy out of nothing. It works by recovering energy that would otherwise be lost, or wasted. It is a classic example of recycling. Instead of expelling ‘wasted energy’ via the exhaust pipe, more heat is extracted from the exhaust gases by a second exhaust turbine downstream from the turbocharger.

The second turbo (the turbocompound turbine) spins at 55,000 r/min. This motion is passed through turbine gears and a hydraulic coupling, then through the timing gears to the crankshaft. Stepping down the revs produces a useful boost in torque, which when reaching the flywheel adds momentum. You get this extra driving force without increasing expenditure on fuel.

The economical green band on the rev counter provides a wide range of economical engine speeds, making life easy for the driver. The engine exhibits great flexibility. The rotation of the crankshaft benefits from the constant extra drive coming from the turbocompounding process, helping to even out the rhythmic pressures induced by combustion. So the engine runs more smoothly.