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A NEW APPROACH TO POWER CREATES NEW CAPABILITIES

As multi-talented as any M Car is, its heart is always the engine. The new M3’s heart is utterly new, and a dramatic departure from the already wonderful engine of its predecessor.

After the resounding success of that special, simpler, less costly engine, BMW M has decided to endow all new M3s with the same engine: a "world engine," and one that does indeed embody the more exotic, costlier, even higher-performance concept formerly reserved for other markets.

Why? Because M owners and enthusiasts demand and expect more; the bar must be raised. The previous engine’s dual overhead camshafts, 4 valves per cylinder, single throttle, "rev range" to a then-impressive 6800 rpm – such features and characteristics have become normal for high-performing regular-production automobiles. To further the M3’s leading-edge position, it was time to move on to an even higher-caliber machine.

Under the new M3’s domed aluminium bonnet, then, is an engine like none other – even more spectacular than the one that powered 2nd-generation European M3s.

AN ALL-NEW BMW M ENGINE: THE S54, WITH NEARLY 100 HP MORE

In its broad concept, the new M3 engine, designated the S54 , shares the familiar layout of other BMW inline 6-cylinder engines. Virtually all of its engineering details, however, are unique and oriented to the very highest level of performance.

Given that other current BMW "sixes" have an aluminum block with cast-iron cylinder liners, it may be surprising that the new M3 engine (like its predecessor) has a cast-iron block. Why?

Compactness is the primary reason. An inline six is longer than a V-6, and BMW nurtures the inline layout because of its superior smoothness and sound. An aluminum block’s cylinder liners take up space; with liners it would not have been possible to achieve the engine’s 3.2-liter displacement without lengthening the block.

The second reason is strength. Given that this engine develops fully 333 hp from 3.2liters – significantly over 100 hp per liter – its internal stresses are immense. According to M3 Project Director Siegfried Friedmann, BMW engineers researched a silicon-impregnated aluminum block (as used in BMW V-8 and V-12 engines), which would not require liners. Butthey became convinced that a cast-iron block could best sustain the engine’s high cylinder pressures and very high piston speed at maximum rpm. (Current Formula 1 engines attain piston speeds around 25 meters per second; with 24 m/sec. at its rpm limit of 8000 rpm, the S54 is very close.)

The block accommodates the engine’s new bore and stroke of 87 x 91 mm; these have increased from the previous U.S. engine’s 86.4 x 89.6 mm to give a displacement of 3246 cc, up from 3152.Increased displacement, however, is not the major contributor to the huge power increase over the previous M3 engine. Playing much larger roles in the nearly 100-hp increase are the new engine’s induction, combustion and exhaust engineering, together with its execution as a high-rpm engine. And the starring role here is played by a brand-new cylinder head that could be termed "exotic."

TOUR DE FORCE: THE CYLINDER HEAD

To achieve more than 100 hp/litre, an engine needs exceptional breathing ability. The new engine’s head is not merely new relative to the previous U.S. M3; it is also new relative to the previous European engine, which delivered 317 hp (SAE net).

Feature-by-feature, the new head (of aluminium as before) differs sweepingly from the previous U.S. head, becoming more like other BMW M cylinder heads. Features shared with the BMW M5’sV-8 engine, for example, are noted with an asterisk (*):

Double VANOS steplessly variable valve timing*. The previous U.S. engine had VANOS variable valve timing on its intake valves only: a 2-stage system, with one timing setting for low, one for high engine speeds. The new engine has stepless Double VANOS, which varies valve timing on the intake and exhaust camshafts without the "step" of the 2-stage system. Though this VANOS is employed in current 3 and 5 Series 6-cylinder engines, as used in the M3engine it varies timing over a wider range and contributes in a major way to the engine’s stratospheric power output. Intake timing is varied by 60°, exhaust by 46°, vs. 40°/25° . As in all BMW engines where it is employed, VANOS is hydraulically actuated in response to electronic controls.



VANOS pressure pump*.
The VANOS system has its own radial-piston hydraulic pump; in regular-production BMW engines the main oil pump supplies the pressure to operate VANOS. This pump is included in the exhaust camshaft’s VANOS mechanism, and produces up to 120 bar (1740 lb./sqin.) of pressure. Herbert Vögele, who directs engine development at BMW M, explains that this high oil pressure enables the M3’s VANOS to vary valve timing more quickly at very high rpm than would the regular-production hydraulic system. Thus BMWM refers to the M3’s VANOS system as High-Pressure Double VANOS.

Unique valve mechanism.
All current BMW double-overhead-camshaft (DOHC) engines employ "bucket-type" hydraulic lifters, actuating the valves directly with minimum noise and no periodic adjustment. For the S54’s rpm potential, BMW M needed a valve train with less reciprocating mass.

To achieve this, they created a different actuating mechanism, using finger-type rocker arms. Pivoting on their own shafts (one on the intake side, one on the exhaust), these small – one could almost say dainty– arms reach out to provide the actuating surface between camshaft and valve. As the entire arm does not move the distance of valve lift, its effective reciprocating mass is less than its actual mass – and it weighs less than the "bucket tappets" in the first place. When all is said and done, the effective mass is 30% less; in turn, this allows lighter valve springs, which also reduce inertia. The lower valve train inertia helps the engine attain its 8000-rpm capability.

As the system involves no hydraulic maintenance of valve clearance, it does have to be inspected periodically. Lead engine engineer Helmut Himmel asserts that it is unlikely that clearance will actually require adjustment, but if so it is done with shims (tiny metal discs of various thickness) without removal of the camshafts.

The rocker-arm arrangement also results in less friction. Unlike the rocker arms of BMW’s V-12 engine, however, these do not incorporate rollers, which would add too much mass for such a high-revving engine.

Where the regular-production 6-cylinder engines have a simplex (single) primary chain driving the exhaust camshaft and a smaller secondary chain driving the intake camshaft from there, the S54 has a full duplex (double) chain driving both cam shafts directly. As usual with BMW engines, the chain is hydraulically tensioned and needs no periodic adjustment or replacement.

Extra-high compression ratio. At 11.5:1, the M3 engine has the highest ratio in current BMW production.(M5: 11.0:1, also quite high.)

Machined surfaces*. "Engineering finery": The combustion chambers and intake ports are completely machined, for smoothness that facilitates airflow. The exhaust ports are partially machined. For durability, the valve seats are of especially hard steel. A3-layer stainless-steel head gasket ensures effective sealing of the head to the block.

Head casting and sealing. Extreme strength in the cylinder head has been achieved by making it a single aluminum casting. This construction, though more difficult to realize than the previous European engine’s 2-piece head casting, also saves weight – a very significant 29lb. As this weight savings is at the top of the engine, it helps lower the car’s center of gravity.

INDUCTION SYSTEM: BMW M TRADITION, STATE-OF-THE-ART TECHNOLOGY

The new M3 returns to a BMW M tradition: an individual throttle for each cylinder. Positioned much nearer the cylinders than a single throttle can be, these bring atmospheric pressure practically right to the cylinder. The "lag time" inherent in airflow into the cylinders is thus greatly reduced and the engine can react more quickly to throttle movements.

In principle, the M3 system– electronically controlled individual throttles – is like that of the M5 even though no actual components are shared. All six throttles operate from a single shaft, each in its own throttle body right at the intake ports. Via the accelerator pedal and its two potentiometers, the driver gives the commands, which in turn are processed by the engine control module and received by a DC servo motor. The motor drives the throttle shaft through a tiny gearbox.

Upstream of (and acoustically decoupled from) the throttle bodies are the six intake trumpets, made of weight-efficient fiberglass-reinforced PA6thermoplastic; their diameter-to-length ratio was calibrated with a computer program of BMW’s Formula 1 racing department. In turn, the trumpets are laser-welded into the induction plenum of the same composite material to form a single assembly.

As on the M5, M Driving Dynamics Control provides Normal and Sport settings for throttle response. In the Sport setting, selected via a console switch, the ratio of throttle opening to pedal movement is increased so that apparent engine response is even quicker. Remarkably, even the transitional response of the electronic engine controls (primarily ignition timing) is altered to suit. Drivers will find one or the other setting more to their liking, or choose them according to driving conditions; the system always reverts to Normal when the engine is started.

Together with the stepless VANOS, this elaborate induction system contributes to the engine’s immense breathing and fuel/air processing capabilities.

EXHAUST SYSTEM: ENGINEERED FOR FREE FLOW

The M engine team led by Messrs. Vögele and Himmel developed one of the freest-flowing exhaust systems ever installed in a production vehicle. After the partially machined exhaust ports, it begins with two elaborately snaking stainless-steel manifolds serving three cylinders each.

These manifolds are formed under high pressure with water inside them, which ensures even distribution of the forming pressure and thus consistent wall thickness. In turn, this process allows stainless-steel walls only 1 mm thick (about 1/25th of an inch), not only helping save weight but also hastening engine warm-up as there is less metal to heat up after a cold start.

Each manifold is a single piece, thus not welded-up as are most headers.

In one of the few differences between the U.S. and European versions of this engine, whereas the Euromodel’s catalytic converters are under the floor pan, in the U.S. version engine each manifold also includes the catalytic converter. This puts the catalysts closer to the engine, improving emission control when the engine is started from cold and meeting more stringent U.S. regulations in this regard. Four Lambda (oxygen) sensors are employed; the engine meets U.S. LEV (Low Emissions Vehicle) limits.

From the catalytic converters rearward, the exhaust system continues as a true dual system through a large, L-shaped muffler/resonator at the rear, which occupies half the under-trunk space that in E46 coupes is devoted to the spare-tire well. From the resonator emerge four polished outlets that speak the authoritative tones of M Power.

This elaborate and efficient exhaust system imposes fully 40% less back pressure on the engine than that of its European-version predecessor, and of course this too contributes to the engine’s enormous breathing and power-producing capacity.

HIGH-PERFORMANCE LUBRICATION AND COOLING

Though their lubrication systems are not identical, there is similarity to the M5 engine in that a "semi-dry-sump" system helps ensure adequate lubrication under the high cornering, acceleration and braking loads the M3 attains. Particularly in hard cornering to the left, there might not be natural return of the oil to a conventional pan; therefore, integrated into the gear-type pressure pump is a scavenging pump (the M5 has two of these) that collects oil from the right side of the small forward oil sump and pumps it back into the main, larger rear sump. This rear sump is almost completely closed off from the rest of the system, and thus able to hold the oil necessary for the required lubrication throughout the engine. Specific return passages are also incorporated into the intake (left) side of the engine to help ensure ideal oil flow under all operating conditions.

The graphite-coated aluminum pistons are cooled by oil spray, and each valve rocker arm is sprayed with oil just as it is about to be loaded by its camshaft lobe.

As on the M5 engine, a thermal sender is employed to monitor both oil level and temperature. If the level drops low, a warning appears in the instrument cluster; the tachometer face includes the oil-temperature gauge.

As on the M5 engine, the M3 cylinder head incorporates cross flow cooling; this promotes consistent temperatures from the front to the rear of the head, helping minimize distortion and wear under the extreme heat such a high-performance engine develops when its full power is being exploited.

THE HIGH-RPM CONCEPT

BMW M engineers chose the S54’s high-rpm concept to achieve high power from moderate displacement. High engine speeds pose challenges; engineers must ensure that durability standards are met and that the engine performs properly at the high rpm levels. As mentioned earlier, the engine’s rev limit is 8000 rpm; its maximum power occurs just below this limit at 7900 rpm. Drivers who mean to enjoy this engine "to the limit" may operate it frequently in these upper reaches of rotational speed.

To achieve the impressive revving capability, the engineers employed a number of detail measures. A forged, nitro-carbonized steel crank shaft provides great strength in this critical component. Forged-steel "crack" connecting rods eliminate the need for bolt sleeves and thus reduce reciprocating weight.

Demonstrating just how many details can go into realizing the high-rpm concept, a unique new water pump plays a role too. The crossflow cooling, essential to the high-speed operation, requires high coolant flow. To achieve this, the engineers developed a pump with 3-dimensionally contoured vanes. Such contours would have been inordinately costly to produce in metal, so BMW M developed a brand-new, novel pump design. Each vane is a small plastic casting, pressed into an also-plastic rotor and then welded into place. Thanks to this innovative impeller, water-pump efficiency has been boosted significantly. Adding future efficiency is a ring-type thermostat, which imposes less resistance to coolant flow than conventional plate thermostats.

Electronics also play a key role in the high-rpm concept. BMW fully developed the S54’s control module: Manufactured by Siemens and called MSS 54, this unit "can do everything, and do it fast," as Helmut Himmel says. Every 6 degrees of crankshaft rotation, it calculates and adjusts the ignition and fuel-injection at each cylinder individually. Ignition takes place through a very small-diameter "pencil" coil at each cylinder, adopted from BMW’s V-12 racing engine and making its first appearance in a production car.

SPECTACULAR RESULTS: POWER, TORQUE, REVS, and PERFORMANCE, SOUND

All this major and detail engineering work results in a remarkable, high-performing, great-sounding sports engine. Powered by its 333 hp through the standard 6-speed manual transmission, the new M3 sprints from rest to 60 mph in a thrilling 4.8 seconds– same as the M5 – and continues on to an electronically limited maximum of 155 mph.

Yet for all this through-the-gears showmanship and the theatrics of upshifting at 8000 rpm, the M3 engine is by no means short on everyday driveability, willingness and auditory pleasure. "Every bit as impressive is the fact that it needs only 5.4 sec. to storm from 50 to 75 mph in fourth gear, which is nearly as quick as the Z8," commented Automobile Magazine in its November 2000 issue.

GREAT LOOKS TOO: THE VIEW UNDER THE HOOD



The S54 engine is engineered beautifully, and also designed to look beautiful. Open the bonnet and you’ll see: Tubing – for the idle air supply, fuel to the injectors, fuel from the fuel pump– is stainless steel. Housed in cast aluminum, the VANOS mechanism projects prominently forward of the cylinder head. Stainless-steel screws secure the camshaft cover. Chrome rings hold the induction trumpets to the ports. The "M" logo adorns the front of the camshaft cover, which also carries a special M oil filler cap. Upper shock/spring-mount covers are special to the M3 too. A long tradition of visually attractive machinery from BMW M (and BMW in general) is advanced another step here.

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