At first glance, turbocompounding seems to defy the laws of physics. In fact 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 gain this extra power without increasing fuel consumption.

The economical green band on the tachometer provides a flexible range of suitable engine speeds, making life easy for the driver. The rotation of the crankshaft benefits from the constant extra drive coming from the turbocompounding process, which helps to smooth out the rhythmic forces induced by combustion.