BMW M5 ENGINE FACTS
Here are all the facts about BMW's hottest V-8:
The V-8's aluminum cylinder block shares the M62's basic architecture (including long-lasting, weight-saving silicon-impregnated cylinder walls) but is a specific casting with 94.0-mm cylinders vs. the M62's 92.0. The stroke is increased from 82.7 mm to 89.0 mm. This results in a displacement of 4941 cc, or approximately 5 liters. "Above all, we wanted to create an abundant torque curve," says BMW M engineer Wolfgang Kreinhšfner modestly - and if that is the goal, to paraphrase what the hot-rodders used to say, "there's no substitute for liters." The cylinder centers are 98.0 mm apart, leaving only 4 mm of block surface between cylinders. For effective sealing with this tight cylinder spacing, BMW M engineers developed new 3-layer steel head gaskets.
Breathing is of course a top priority; BMW M spared no expense in developing the S62's induction system.
Air is taken in at two points behind the front bumper, passes through two intake silencers and two hot-film air-mass meters, and then flows into the voluminous carbon-fiber plenum atop the engine. From there, air courses through 230-mm intake runners (including the throttle housings) to the individual cylinders. The entire assembly of plenum and runners is attached to the throttle housings via a rubber/metal flange (one per bank) that acoustically and thermally decouples the plenum from the engine itself.
Admission of air to the cylinders is not through "a throttle," but through eight individual throttle butterflies, one for each cylinder. Individual throttles are a very costly feature, reserved for the highest-performance engines - including racing powerplants. Previous large M 6-cylinder engines, powering M1, M5 and M6 models, all had this feature; but the S62 is the first BMW engine with electronically actuated individual throttles. Positioned much nearer the cylinders than a single throttle can be, these throttles eliminate a "lag time" inherent in airflow and allow the engine to react much more quickly to throttle movements.
Each throttle operates in its own housing, mounted directly at the intake ports. Via the accelerator pedal and its two potentiometers, the driver gives the commands. In turn, these commands are processed by the engine control module and received by a DC servo motor between the cylinder banks. In turn, through a tiny gearbox, this motor drives a shaft that drives a link to each bank to rotate the four throttles of that bank.
These two links rotate the two throttle shafts, connecting via ball joints at cylinders 3 and 6. From these points, the other three throttles (each 50 mm in diameter) of each bank are opened and closed. The servo motor reacts to any pedal movement in a lightning-fast 120 milliseconds, so the driver perceives no lag time; via the M Driving Dynamics Control system, there are two settings for throttle response: Normal and quicker Sport.
The throttles of cylinders 4 and 8 also have their own feedback potentiometers to monitor the throttles' operation. If a fault is recognized, the system switches to one of four "limp-home" modes that can allow operation at up to 62 mph.
The S62 is BMW's first V-8 engine equipped with Double VANOS, a system that steplessly varies the timing of both intake and exhaust valves on both cylinder banks.
Current BMW 2.5 and 2.8-liter 6-cylinder engines also have the Double system; current "regular" V-8s have a Single VANOS system that steplessly varies intake-valve timing. In addition to enhanced low to medium-speed torque, the advantages of VANOS include:
- Reduced unburned hydrocarbons during idling
- Smoother idling
- Internal exhaust-gas recirculation at low speeds for improved control of oxides of nitrogen (Nox)
- Quicker warmup of the catalytic converters after a cold start, therefore reduced emissions during this operational phase
As on other BMW engines, the VANOS mechanisms are at the front of the cylinder heads. The 1450 psi of hydraulic pressure used to actuate VANOS is provided by dedicated oil pumps, one per cylinder head. Valve timing is varied over a range of 60o in terms of crankshaft rotation, a wider adjustment range than that of other BMW engines.
The S62 has its own unique Motronic control system, designated MSS 52, which oversees:
- Basic engine functions
- Electronic throttle system (incorporating influences of cruise control and Dynamic Stability Control)
- G-sensitive lubrication system
- Thermal oil-level sender
- Variable tachometer warning zone
- Catalytic-converter protective functions
- Double VANOS variable valve timing
- Maximum engine speed (7000 rpm)
- M Driving Dynamics Control, which provides two settings for the throttle system and power steering.
For optimum power output, the engineers designed specifically shaped cutouts in the piston crowns for the intake and exhaust valves. This requires a different piston design for each cylinder bank, rather than the usual identical design for all pistons. Via two separate oil passages in the crankcase, the pistons are oil-cooled. The compression ratio is 11.0:1, a full point higher than for the 4.4-liter V-8; this too contributes to the engine's high power and torque output.
Oil-cooled
pistons were designed for the two cylinder banks
For optimum power output, the engineers designed specifically shaped cutouts in the piston crowns for the intake and exhaust valves. This requires a different piston design for each cylinder bank, rather than the usual identical design for all pistons. Via two separate oil passages in the crankcase, the pistons are oil-cooled. The compression ratio is 11.0:1, a full point higher than for the 4.4-liter V-8; this too contributes to the engine's high power and torque output.
G-sensitive
lubrication system
Given the 45 degree cant of the cylinder banks and the M5's cornering capability of over 1g, natural return of oil to the sump might have been inadequate during extreme cornering. Thus the M engineers devised a unique system to ensure effective engine lubrication at all times.
In addition to the usual pressure pump, there are two scavenging pumps, one for each cylinder bank. In straight-ahead driving, these pumps pick up oil from the rear of the engine and return it to the sump. In hard cornering (0.9g or more), the Dynamic Stability Control system's lateral-g sensor switches magnetic valves to different pickup points, at the outer side of each head and the oil pan. This system remains active even if the driver switches off the DSC.
The oil level and temperature are monitored by a thermal sensor; a warning appears in the Check Control display if the level falls low, and an oil-temperature gauge is included in the tachometer face. Oil is cooled by a coolant-oil heat exchanger, the first ever used on a gasoline engine.
Modified
cylinder heads
The V8's two cylinder heads are modified to include super-efficient crossflow coolant flow and enlarged intake ports. Other significant features of the cylinder heads include:
- Hollow camshafts of nodular cast iron for reduced inertia and long life.
- Specific valve timing - The S62's 35-mm intake and 30.5-mm exhaust valves are shared with the M62 engine, but valve timing is specific to this engine: The intake valves are open 252 degrees and the exhaust valves 248 degrees, with Double VANOS shifting their timing to vary overlap. As in other current BMW V8 and 6-cylinder engines, the valves are actuated by no-maintenance bucket-type hydraulic lifters.
Specific
cooling system
An all-new water pump, capable of pumping 380 liters per minute, was developed to meet the engine's heightened thermal needs.
Special
camshaft drive
In place of the M62 engine's simplex roller chain driving both intake camshafts, the S62 employs a heavier-duty duplex chain. As in the M62, the exhaust camshafts are driven from the intake camshafts via simplex chains.
Low-back-pressure
exhaust system
Exiting the engine through double-wall stainless-steel exhaust headers (as on the M62 engine), exhaust gases then flow through one catalytic converter per cylinder bank. There are four oxygen sensors: two ahead of the converters, two behind. A pressure-equalizer passage connects the two exhaust streams behind the converters, enhancing low-speed torque and contributing to the engine's wonderful exhaust sound. Aft of the catalytic converters, the full dual exhaust system includes two mufflers and two resonators and ends in four glistening stainless-steel outlets.
Variable
tachometer warning zone
This innovation reminds drivers that a cold engine - especially a high-performance one - should be treated with care. When the engine is first started, the tachometer's warning zone (indicated by orange LEDs) begins at 4000 rpm. As the engine warms, LEDs are extinguished to lift the limit in increments of 500 rpm until the warning field begins at its normal 6500 rpm. The actual rpm limit is 7000.