The BMW S85B50 is a naturally aspirated V10 petrol engine which replaced the BMW S62 V8 engine in the M5 model and was produced from 2005–2010. It was both BMW's first and only production V10 engine, and the first petrol V10 engine to be available in a production sedan (saloon). Introduced in the E60 M5, the S85B50was inspired by BMW's previous Formula One involvement. Unlike most other BMW M engines, the S85 is not related to a regular production BMW engine. The BMW S65 V8 engine (used in the E92 M3) is based on the S85.

Nomenclature

As the S85 was BMW's first V10 engine, it was given a new series in the BMW's engine codes. The "60s" were used for V8 engines and the "70s" were used for V12 engines, therefore the V10 was allocated in the "80s" (despite having fewer cylinders than the V12 engines in the "70s".) The engine code for the related BMW S65 V8 engine reflects its link to the S85. The S65 code was selected to signify that the V8 is largely derived from the S85 minus two cylinders, and not related to BMW's other V8s.

Design

The S85 has dual overhead camshafts with four valves per cylinder and double-VANOS (variable valve timing). The engine block and cylinder head are constructed from aluminum alloy. Peak power is 373 kW at 7,750 rpm and peak torque is 520 Nm at 6,100 rpm. The redline is 8,250 rpm, and the specific output of undefined kW per litre is amongst the highest of naturally aspirated production car engines. Features include:

Performance

The S85 is lauded for its high-revving nature, capable of reaching redline at 8,250 RPM, a rarity for road-going V10 engines at the time of its release. Its performance figures were notable for its era, producing 100 hp per liter, one of the highest outputs for naturally aspirated engines at the time. The engine allowed the BMW M5 and M6 to accelerate from 0 to 100 km/h (62 mph) in around 4.5 seconds. Additionally, it featured a 7000-RPM launch control function for optimised acceleration.

Reliability and Design Flaws

Despite its engineering pedigree, the S85 notably suffers from significant reliability issues. Maintaining the S85 V10 requires due diligence from the owner. To ensure longevity, regular oil changes, close monitoring of VANOS function, and early replacement of rod bearings and throttle actuators are critical and warrants S85 owners to follow a proactive and a meticulous maintenance schedule.

Awards

The S85 has won the following awards at the International Engine of the Year:

Legacy and Impact

The S85 V10 engine remains a revered engine in BMW’s history, praised for its incredible power delivery, high-revving characteristics, and direct links to BMW’s Formula 1 technology. However, due to its reliability issues and expensive maintenance, the engine has a mixed reputation among owners and enthusiasts. Despite this, the S85 is often considered one of the greatest engines ever built by BMW. With the end of its production in 2010, BMW transitioned away from naturally aspirated engines in favour of turbocharged power-plants, marking the end of an era for BMW’s high-revving, naturally aspirated performance engines.

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