BMW's M5 V10 Engine

This article was first published in 2004.

The new BMW M5 uses a naturally aspirated, 5-litre V10 engine developing 507hp (373kW) at 7750 rpm and 520Nm at 6100 rpm. In this story we take a look at the internals of this astonishing engine.

The engine weighs 240kg, about the same as the previous M5’s V8 engine. It uses a 90-degree angle between the two banks of 5 cylinders, with a 17mm crankshaft offset. The cylinder crankcases are made of low-pressure gravity die cast hypereutectic aluminium-silicon alloy. No liners are present - the iron-coated pistons run up and down in the uncoated bores. A short-stroke design is used - stroke is 75.2 mm and bore is 92 mm.

A ‘bedplate’ (a crankshaft girdle) is used to tie the bottom of the engine together. The bedplate is made from aluminium with integral grey cast iron inserts used to ensure crankshaft alignment and keep the main bearing clearance at a minimum over the entire operating temperature range. The inserts help to reduce the thermal expansion of the aluminium bedplate.

The crankshaft is made of forged, high-tensile steel and is supported by six bearings. It weighs 21.8 kilograms. The main bearing diameter is 60mm with a bearing width of 28.2mm. Two conrods connect to each of the five crank pins, which are offset at an angle of 72 degrees. A cylinder spacing of 98 mm enables the use of a short crankshaft.

The pistons are made of high temperature resistant aluminium alloy and are provided with an iron coating. They weight 481.7 grams each, including piston pins and rings. The compression height is 27.4 mm at a compression ratio of 12.0:1. The pistons are cooled using oil spray jets which are directly connected to the main oil duct. The 140.7 millimetre long fracture-split trapezoidal connecting rods are also made of high-strength steel. Each of the connecting rods - forged from 70MnVS4 - has a mass of only 623 grams, including the bearing shells.

As are the crankcases, the single-piece aluminium cylinder heads of the V10 engine are cast at the BMW light alloy foundry in Landshut. The cylinder heads feature integrated air ducts for air injection, important for rapid catalytic converter warm-up.

The valves are actuated by spherical tappets featuring hydraulic valve play compensation. The tappet diameter has been reduced to 28 millimetres and mass to 31 grams. The diameter of the intake valve is 35 millimetres, the exhaust valve measures 30.5 millimetres in diameter. The shafts are 5 mm in diameter.

The bi-VANOS variable camshaft control ensures an optimum charge cycle. At the lower end of the load and engine-speed scale, the car can be driven with an increased valve overlap, boosting internal exhaust gas recirculation. This, in turn, leads to a reduction in charge cycle losses and fuel consumption. The adjustment of the angles as a function of the accelerator pedal position and the engine speed is infinite and map-controlled. The sprocket, which connects to the crankshaft via a simplex chain, is linked to the camshaft via a two-speed, helical gearbox. In the event of an axial displacement of the adjusting piston, the helical set of teeth turns the cam relative to the sprocket, which allows for the variation of the angle of the intake camshaft by up to 66 degrees and the outlet camshaft by a maximum of 37 degrees in relation to the crankshaft. The M bi-VANOS technology requires very high oil pressures for ultra-precise, high-speed camshaft adjustment. This is why a radial piston pump in the crank chamber increases engine oil pressure to an operating pressure of 80 Bar. 

Four oil pumps provide the engine with lubricating oil. During extreme cornering, centrifugal forces push the engine oil to the cylinder bank facing the outside of the bend, thereby preventing the natural return of oil from the cylinder head, which might lead to inadequate oil supply in the sump. Should the worst happen, the oil pump could suck air. To prevent this situation, the engine features a transverse force regulated oil supply system. This system incorporates two electrically-operated duo-centric pumps which pick up oil from the outer cylinder head and transport it to the main oil sump if lateral acceleration exceeds 0.6 g. A lateral-g sensor transmits signals to the pumps.

The oil pump itself is a continuously variable pump with volume control which delivers exactly the amount of engine oil needed by the engine. This is achieved by the variable eccentricity of the pump’s rotor in relation to the pump casing, depending on the oil pressure in the main oil duct. This picture shows the oil pump at minimum flow....

...and this at maximum flow.

Each of the ten cylinders has its own throttle valve. In order to attain maximum engine responsiveness in the lower speed range and to achieve an immediate vehicle response at the high end of the performance spectrum, all throttle valves are controlled fully electronically. Two contactless Hall potentiometers determine the position of the accelerator pedal 200 times per second. The engine management reacts to changes and causes the two actuators to adjust the ten throttle valves. It takes 120 milliseconds to completely open the throttle valves.

The V10 engine uses ten flow-optimised intake trumpets to breathe air from two intake plenums. The intake plenums and the trumpets are made of a lightweight compound material that contains 30 percent fibreglass.

Two stainless steel 5-into-1 high-performance tubular headers have been optimised for equal length. For exact pipe diameters, the seamless stainless steel pipes are formed from the inside using an interior high-pressure forming technique (hydroforming) with a pressure of up to 800 Bar. The manifold pipes have a wall thickness of just 0.8 mm.

The exhaust system has a dual-flow design all the way to the silencers. Two trimetal-coated catalytic converters per exhaust line clean the exhaust gases in compliance with the European EU4 and American LEV 2 standards. There are two underfloor catalysts. The other two catalytic converters (one for each exhaust line) are located close to the engine. In conjunction with the thin-walled exhaust manifolds, these catalysts quickly reach their optimum operating temperature.

The MS S65 engine control module is equipped with three 32-bit processors that perform more than 200 million individual calculations per second. Compared to the M3 control unit presented only four years ago, this represents a performance increase by a factor of eight. In terms of memory capacity, the latest control unit outdoes the previous one by as much as ten times. Receiving more than 50 input signals, this system calculates for each individual cylinder and for each individual cycle the optimum ignition point, the ideal cylinder charge, the injection quantity and the injection point. At the same time this system calculates and makes the necessary adjustments for the optimum camshaft angle and the optimum position of the ten individual throttle butterflies.

Ionic current technology (as used by Saab for some time) is used by the engine management unit to detect engine knock, misfiring and combustion misses. This technology utilises the spark plug in each cylinder to sense and control engine knock. It also helps to check for correct ignition and to identify possible ignition misses. The spark plug therefore has a dual function – as an actuator for the ignition and as a sensor for monitoring the combustion process.

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