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 S85 was inspired by BMW's previous Formula One involvement.[1] Unlike most other BMW M engines, the S85 is not related to a regular production BMW engine.[2]
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.[3]
Design
Compilation of the four side views of the BMW V10 engine as it is installed in the BMW M5 and M6
Version
Year
Displacement
Power
Torque
S85B50
2005–2010
4,999 cc (305.1 cu in)
373 kW (500 hp) at 7,750 rpm
520 N⋅m (384 lb⋅ft) at 6,100 rpm
The S85 has dual overhead camshafts with four valves per cylinder and double-VANOS (variable valve timing).[4] The engine block and cylinder head are constructed from aluminum alloy.[5]
Peak power is 373 kW (500 bhp) at 7,750 rpm and peak torque is 520 N⋅m (384 lb⋅ft) at 6,100 rpm.[6]
The redline is 8,250 rpm,[2] and the specific output of 74.6 kW (100.0 bhp) per litre is amongst the highest of naturally aspirated production car engines.
Application of an "ionic current measuring system" for knock sensing.[10] The ionic current system uses a low voltage applied across the spark plugs immediately following the ignition spark, and can detect misfires as well as knock.
Quasi-dry sump lubricating system where the engine has 2 oil sumps that hold oil, and oil pickup is enhanced by secondary electrical scavenge pumps that feed oil from the smaller sump to the main sump[11]
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.[13]
Reliability and Design Flaws
Despite its engineering pedigree, the S85 notably suffers from significant reliability issues.
One of the most notorious problems is rod bearing wear, which can occur prematurely, often around 80,000 km or roughly 50,000 miles. The root cause is attributed to the engine’s high-revving nature, tight tolerances and a lack of clearance between the rod bearings and the rod journals. The S85 operates at very high RPMs (up to 8,250 RPM), and the lack of sufficient lubrication combined with high pressures leads to increased wear on the bearings, potentially resulting in catastrophic engine failure if not replaced preemptively. The original maintenance intervals for oil changes were too long for these conditions, exacerbating the issue. Hence, replacement of rod bearings preemptively as part of preventive maintenance and shortening oil change intervals are paramount to engine longevity. [14][15]
Another common issue involves the VANOS system, which controls the variable valve timing. The VANOS solenoids and high-pressure oil lines can degrade over time, leading to erratic performance or engine fault codes. The complexity of the system, combined with high oil temperatures, can cause these components to fail prematurely.[16]
Throttle actuator failures are also a known problem. These actuators control the throttle response in the S85’s individual throttle bodies. Over time, the gears within the actuators wear down, leading to a loss of throttle control or limp mode. This issue is particularly problematic due to the engine’s dependence on precise throttle control for its high-performance output.[14][17]
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.
2005 International Engine of the Year, Best Performance Engine, Best Above 4.0 Litre, Best New Engine
2006 International Engine of the Year, Best Performance Engine, Best Above 4.0 Litre
2007 Best Performance Engine, Best Above 4.0 Litre
2008 Best Above 4.0 Litre
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.[7]
