UNDER the B4's bonnet is a 2.0-litre, DOHC 16-valve, twin turbo engine that produces 190kW of power at 6400rpm and peak torque of 320Nm at 4800rpm. The H4-2.0 two-stage twin-turbo powerplant has a primary turbo unit for low-end torque and a secondary unit for top-end power. At least 278Nm of torque is on tap from 2000rpm, while the engine is still producing 300Nm at 6000rpm, which gives the B4 a wider and flatter torque band than is possible with an engine equipped with a single turbocharger. Notable features of the B4's engine include forged pistons that are considerably stronger than those on the standard Liberty, sodium-filled exhaust valves which help to cool the valve head faster by transferring heat from the head to the valve stem, hollow intake valves which produce less inertia and subsequently less wear of the valve train, and an engine oil cooler located between the oil filter and engine block. In Japan, the B4's engine produces 206kW, but in Australia we have to make do with a less powerful specification courtesy of our lower quality fuel. Japanese market models have been designed to run on 100 RON fuel. The Australian-spec B4's minimum fuel octane-rating requirement is 98 RON, although it can cope with a few tankfuls of standard premium unleaded, which is rated at 95 RON. However, using regular unleaded petrol (91 RON) has the potential to cause damage to the engine.