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BMW S65 engine
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ManufacturerBMW, Bayerische Motoren Werke AG
PredecessorBMW S54
Bore92 mm
Stroke75.2 mm
Displacement4.0 L (3999 cc/244 in³)
Length734 mm
Compression ratio12.0:1

The S65 is a naturally-aspirated DOHC 32-valve automobile V8 engine from BMW. Derived from the BMW S85 V10 engine used in the M5/M6, it shares the same basic architecture and aluminium construction. It was introduced in the E92 M3 as a replacement for the S54 straight-6.

Engine Displacement Power Torque Redline Year
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.[1] The S54 engine had reached the end of its development potential, making it clear a new engine was needed.

The S65 shares the same 92 mm bore and 75.2 mm stroke cylinder dimensions with the S85 V10, along with the Double-VANOS variable valve timing system and 12.0:1 compression ratio.

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.[2]

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.

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S65 engine with the top plastic air plenum removed to reveal the 8 individual throttle bodies.

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.[1]

The resulting engine weighs 202 kg (445 lb): 15 kg (33 lb) lighter than the straight-6 engine it replaces, while also being shorter.[3]

The firing order for the S65 engine is 1-5-4-8-7-2-6-3, which is different from the typical BMW V8 firing order of 1-5-4-8-6-3-7-2 [1]


See also