|S65B40||4.0 L (3999 cc/244 in³)||309 kW (414 hp) @ 8300||400 N·m (295 ft·lbf) @ 3900||8400||2007|
The S65B40 was developed as a result of increasingly stringent Euro V and CARB emissions regulations. The S54 engine had reached the end of its development potential, making it clear a new engine was needed.
However, the V8 does differ in a number of crucial aspects from its V10 sibling. The VANOS system is operated from engine oil-pressure, negating the need for a separate high-pressure hydraulic system as fitted to the S85. New lightweight spark coils with integrated knock sensors are fitted to each cylinder, bringing the total sensor count to eight compared with two on the V10. This allows more accurate detection of knocking with the added benefit that the eight sensors actually weigh less than the previous two sensor setup.
A conventional wet-sump lubrication system with two oil pumps replaces the three-pump dry sump system used on the V10, further decreasing weight. The alternator disconnects from the engine during acceleration to maximise power, only charging the battery during braking whenever possible, in a system BMW calls Brake Energy Regeneration.
The die-cast, over-eutectic aluminium-silicon engine block is sourced from BMW's Landshut F1 foundry, while aluminium cylinder heads come from Hydro-Aluminium in Austria. Other notable features of the engine include lightweight iron-coated aluminium pistons, steel-magnesium connecting rods, forged steel crankshaft and eight throttle butterflies.
An updated version of the Siemens MS S65 ECU (used in the S85 V10) is fitted to the V8. Claimed to be capable of more than 200 million calculations per second, the new ECU (known as the MS S60) comfortably exceeds the 25 million calculations of which the S54's ECU was capable.
The resulting engine weighs 202 kg (445 lb): 15 kg (33 lb) lighter than the straight-6 engine it replaces, while also being shorter.