Drives: E70 BMW X5 4.8i
Join Date: Oct 2006
Location: Northern Europe
Originally Posted by replicat
I like to read that if it not to much trouble.
My thoughts on the engine (S54B32) We're mixed at first, I was just getting into cars back then, im only 20 now
I thought that the engine was terrible because it was only a 12HP more than the S52B32) And yet the e46 weighed 240 pounds more. Then as I started getting more and more into cars and I saw how different the two were, from a technological/dynamic standpoint and was like "Oooooohhhhh, I get it now"
Well, here you go. After this, you'll know more about the S54B32 than even most BMW service techs do. And about the M Differential Lock and the SMG-II as well.
As multi-talented as any M Car is, its heart is always the engine. Under the M3’s domed hood, then, is an engine like none other. In its broad concept, the M3 engine, designated the S54 , shares its format with 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 S54 M3 engine 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 3.2 liters – 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. They concluded 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 reportedly attain piston speeds around 25 meters per second; with 24 m/sec. at its rpm limit of 8000 rpm, the S54 is quite close.)
The block accommodates the engine’s bore and stroke of 87.0 x 91.0 mm, up from the regular-production BMW 3.0-liter six’s 84.0 x 89.6 mm. However, playing much larger roles than increased displacement in the nearly 100-hp increase over the most powerful 3 Series engine are the M3 engine’s induction, combustion and exhaust engineering, together with its execution as a high-rpm engine. The starring role here is played by a cylinder head that could be termed “exotic.”
Tour de force: the cylinder head
Feature-by-feature, the cylinder head (of aluminum) joins exemplifies the tradition of BMW M cylinder heads. Its key features include:
Double VANOS steplessly variable valve timing. The S54 engine has stepless Double VANOS , which varies valve timing on the intake and exhaust camshafts. Though Double VANOS is employed in all other current BMW engines, as used in the M3 unit it varies timing over a wider range and contributes in a major way to the engine’s stratospheric power output.
VANOS pressure pump. The M3 VANOS system has its own radial-piston hydraulic pump; in regular-production BMW engines the main oil pump supplies the pressure to operate VANOS. Integral to the exhaust camshaft’s VANOS mechanism, the pump produces up to 120 bar (1740 lb./sq in.) 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 the very high rpm it reaches. Thus BMW M refers to the M3’s VANOS system as High-Pressure Double VANOS.
Unique valve mechanism. Regular-production BMW 6-cylinder engines employ bucket-type hydraulic lifters, actuating the valves directly with minimum noise and no periodic adjustment. For an engine with the S54’s rpm potential, BMW M engineers needed 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 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 further reduce inertia. The system also has less friction.
As there is 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 ever require adjustment, but if so it is done with shims (tiny metal discs of various thickness) without removing the camshafts.
Whereas the “regular” 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 camshafts 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. (The 760Li’s V-12 engine comes close with 11.3:1.)
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. A 3-layer stainless-steel head gasket ensures effective sealing of the head to the block.
Head casting and sealing. Extreme strength in the cylinder head is achieved by making it a single aluminum casting. Though more difficult to realize than the previous European engine’s 2-piece head casting, this construction also saves a significant 29 lb. And as this weight reduction is at the top of the engine, it helps lower the car’s center of gravity.
BMW M tradition, state-of-the-art technology
The M3 manifests an important BMW M tradition: an individual throttle for each cylinder. Positioned much nearer to 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 the M3 system of electronically controlled individual throttles, 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 the throttle bodies are the six intake trumpets, made of weight-efficient fiberglass-reinforced PA6 thermoplastic; these are laser-welded into the induction plenum of the same material to form a single assembly.
M Dynamic Driving Control provides Normal and Sport settings for throttle response. In Sport, selected via a console switch, the ratio of throttle opening to pedal movement is increased so that apparent engine response is even quicker. Even the transitional response of the electronic engine controls is altered to suit. Drivers tend to find one or the other setting more to their liking, or choose them according to driving conditions or mood. The system always reverts to Normal when the engine is started.
Together with the stepless VANOS, this elaborate induction system adds to the engine’s immense breathing and fuel/air processing capabilities.
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 headers serving three cylinders each.
These headers are formed under high pressure with water inside them, which ensures an 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 warmup as there is less metal to heat up after a cold start.
Each header 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 Euro model’s converters are under the floorpan, in the U.S. version engine each header 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 complies with 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 and 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 power output.
High-performance lubrication and cooling
To help ensure adequate lubrication under the high cornering, acceleration and braking loads the M3 attains, the S54 engine employs a “semi-dry-sump” oiling system. Particularly in hard cornering to the left, it is critical to ensure return of oil to the pan; therefore, integrated into the gear-type pressure pump is a scavenging pump 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 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.
A thermal sender monitors oil level and temperature. If the level drops low, a warning appears in the instrument cluster; the tachometer face includes the oil-temperature gauge.
The M3 cylinder head incorporates crossflow 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
High engine speeds are essential to achieving such high power from moderate displacement, but they pose challenges; engineers must ensure that durability standards are met and that the engine performs properly at these levels. The M3 engine’s maximum power occurs just below its 8000-rpm limit at 7900 rpm.
To achieve the revving capability, the engineers applied a number of detail measures. A forged, nitro-carbonized steel crankshaft 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 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 novel pump design. Each vane is a small plastic casting, pressed into an also-plastic rotor and then welded into place. Also adding cooling efficiency is a ring-type thermostat, which imposes less resistance to coolant flow than a conventional plate thermostat.
Electronics play their role too. BMW fully developed the S54’s control module: Manufactured by Siemens and called MS S54, 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.
Power, torque, revs, 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 M3 coupe 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. In a March ’03 comparison test, Road & Track that “the M3’s engine possesses an uncannily smooth power delivery. Not only smooth, but also flexible, the M3’s six has a wide, usable powerband. Midrange punch is already good, but once above 4000 rpm, the engine adopts an even more menacing snarl as it pulls strongly right up to the redline.”
Great looks too:
the view under the hood
Following a long BMW M tradition of visually attractive machinery, the S54 engine’s appearance is as beautiful as its engineering. 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 and a special M oil filler cap adorn the front of the camshaft cover.
getting S54 power to the road
Like every M Car to date, the M3 transmits its power to the road via classic rear-wheel drive ; the M3 packs some premium and fascinating engineering into its drivetrain.
6-speed manual transmission. Both M3s come standard with the robust and precise Getrag Type D 6-speed manual transmission, crisply controlled by a shift knob with illuminated shift pattern and M logo.
The transmission housing incorporates NACA air intakes which, together with careful aerodynamic design of the underbody, help keep internal transmission temperatures down; the engineers speak of 30°C (about 55°F) cooler oil than if these measures had not been taken.
Super-sized differential unit. Significant modification in the rear-suspension area, including an all-new subframe, has allowed equipping the M3 with the same heavy-duty differential dimensions as in the 394-hp M5, whose production recently ended. A special high-strength steel alloy, called 18CrNiMo7, is used for the differential gears to achieve superior quietness and durability. A relatively “short” final drive ratio, 3.64:1, exploits the engine’s generous torque and rpm range; the 6th gear keeps it humming moderately at cruising speeds. Here too, targeted airflow under the vehicle helps keep the oil cool, along with a ribbed differential case.
M Variable Differential Lock. Together with the German division of GKN Viscodrive, BMW M engineers developed a special mechanical limited-slip differential for the M3s.
The principal (and principle) difference between a traditional limited-slip “diff” and this M Variable Differential Lock is that the former senses torque, the latter senses wheel speed (rpm). Under dry to not-quite-dry road conditions, the traditional limited-slip has long enhanced the handling of sporty rear-wheel-drive BMWs; however, under slippery conditions, this differential type has limited ability to improve traction. On all current BMW models, electronic traction control addresses this issue.
The M Variable Differential Lock specifically addresses low- and split-traction situations in a way that reinforces sporty handling, imparting to the M3 a slippery-road ability no previous high-performance, rear-wheel-drive sports car ever had.
Any time a speed difference develops between the two rear (driven) wheels, a shear pump, driven solely by this difference, develops pressure in the silicon viscous fluid in which the lock operates. In turn, this pressure is directed to a multi-disc clutch that transfers driving torque to the wheel with the better road grip (“select high”). The greater the speed difference between the two wheels, the more aggressively the clutch engages. As soon as the difference between the two wheels’ speeds begins to diminish, the clutch starts to ease off.
This mechanism is “elegant,” in that it achieves sophisticated action by entirely natural means. There is no external pump, no external source of lubrication or operating fluid. The very motion to be controlled – differences in speed between left and right wheels – generates its locking action. Viscous fluid is so-called because it develops internal force (via an increase in viscosity) whenever it is sheared; this is why the relatively small difference between one wheel speed and the other can generate the necessary action.
Dynamic Stability Control. This electronic traction and stability system, standard on all current BMWs, complements the M Variable Differential Lock.
DSC optimizes traction by electronic means, sensing wheel-speed differences and reducing engine torque and/or applying individual rear-wheel brakes. The crucial difference to the M3 driver between the M Variable Differential Lock and the DSC traction function is that the former in no way impedes power delivery, and is hence suitable for performance driving.
Yet in fact, even DSC’s traction function in the M3 is calibrated to M-specific parameters. In cooperation with Continental Teves, BMW M engineers developed a logic that, in combination with the fast-reacting engine, performance-oriented gearing and M Variable Differential Lock, achieves the desired traction optimization in a more M-compatible way…in other words, without undue interference with M3 performance and the differential lock’s ability to get power to the road.
The DSC stability-enhancing function is essentially unrelated to traction. Sensing differences in wheel speed in a critical cornering or avoidance maneuver, DSC detects any deviation from the normal cornering path (abnormal understeer or oversteer) and gently applies individual wheel brakes to help the driver keep the vehicle on the intended path.
Sequential Manual Gearbox (SMG):
a special way to drive a performance automobile
Given the M3’s performance nature, it does not seem logical to offer an automatic transmission as such; no matter how good – and BMW’s 5- and 6-speed automatics are among the best – an automatic transmission incurs some performance loss relative to a well handled manual gearbox. On the other hand, given today’s capabilities in electronics and hydraulics, it does make great sense to enhance the M3’s 6-speed manual transmission with some automated operation. This is accomplished with the optional Sequential Manual Gearbox (SMG).
In conceptual terms, the SMG system consists of –
• The same 6-speed manual transmission as is standard in M3 models.
• An electrohydraulic mechanism that does the actual gearshifting and clutch actuation.
• Electronic controls that regulate the electrohydraulic mechanism.
• The driver interface, which includes a shift lever on the console and shift “paddles” on the steering wheel.
There is no clutch pedal. On the console is a short, sporty shift lever with R (Reverse), N (Neutral) and S/A (Sequential/Automated) positions, plus “–” and “+” directions. The shift pattern appears on the shift knob and in an instrument-cluster display. Behind the shift lever is a program selector, with which the driver may select –
• In the Sequential mode, 6 programs ranging from “softest and slowest” shifts to “firmest and quickest” shifts; i.e. from most leisurely to sportiest.
• In the Automated mode, 5 programs of similar gradation.
In the dash display, the selected program is shown in a bar graph that repeats the graphic of the program selector switch. The gear currently engaged is shown as a numeral at the left of the indicator; in A, an “A” appears next to the gear indication. At the right side of the shift pattern, “S” is shown if the automated mode is currently engaged, and vice versa; this indicates which mode will be obtained if the lever is moved in that direction.
The vehicle may be parked in R or S/A, not N. To start the engine, the selector must be in N and the brake pedal applied. This accomplished, the driver then selects R or S/A (again with the brakes applied). When moving off from rest in A, the system automatically selects 1st gear, and shifts up through the gears to 6th as road speed increases. In this sense, the A mode resembles the operation of an automatic transmission – but only resembles, not duplicates, it.
Sequential (S) mode. In this mode, the driver has full control over shifting. Pulling the shift lever rearward in the “+” direction, or actuating the right-hand “paddle” on the steering wheel, effects upshifts; pushing the shifter forward (“–”) or actuating the left-hand paddle effects downshifts. It’s that simple:
• S1-5: Selected by the console switch and indicated in the instrument-cluster display, the programs range from “softest” to “firmest” – that is, in 1 the shifting is accomplished at a relatively leisurely pace, in 5 much more quickly. The driver’s criterion here is how sportily he or she wants to drive; in any of the programs, the higher the engine speed the quicker the shift.
• S6: To select this most race-like program, the driver must switch off the Dynamic Stability Control system. Minimum shift time in S6 is 80 milliseconds; under equal conditions, the “slowest” shift program (1) takes 2-4 times as long to complete a shift.
The word “sequential” signifies the basic concept of “one gear at a time” – each tip of the shift lever or shift paddle moves the transmission up or down one gear. However, the driver can skip gears by simply hitting more than one shift in quick succession. Whenever and however the driver calls for a shift, the response of SMG is immediate and satisfying.
Automated (A) mode. Though automated, this DRIVELOGIC mode is not meant as a substitute for a conventional automatic transmission. Here there are five programs. As with S, the higher the program number the faster the shift; in A, however, the speeds at which shifts occur (both up- and downshifts) also increase. For example, in A1 with 35% throttle opening, the upshift to 6th gear will occur about 40 mph; in A5, not until about 80 mph. Decelerating at 5 m/sec/sec, DRIVELOGIC would shift down two gears from 6th to 4th at around 30 mph in A1, or from 6th to 5th at about 106 mph in A5. A2 through A4 effect shifts at points in between.
Additional capabilities and safeguards. Careful development of DRIVELOGIC has resulted in many fine points of the system’s operation:
• 1st-gear start in S: As the vehicle comes to a stop in the S mode, DRIVELOGIC automatically selects 1st gear for starting off again; the driver will then effect upshifts as desired.
• 2nd-gear start: A1 can be used as a winter-driving program; it starts the vehicle from rest in 2nd gear to move off gently. (Dynamic Stability Control’s traction function also guards against wheelspin.)
• Overspeed protection: If the driver calls for a downshift (S mode) that would overspeed the engine, the command to downshift is ignored.
• In any A program, a floored accelerator can get one or two downshifts depending on conditions, and pleasingly quickly.
• Slip detection: In both S and A modes, this safeguard helps keep the vehicle stable during downshifts, particularly when traction is low. Every 10 milliseconds, the rear wheels are checked by the DSC for slippage. If there is too much decelerative torque on the wheels, clutch engagement and engine speed are automatically adjusted to prevent too abrupt a downshift.
• Double-clutching. Also in both modes, DRIVELOGIC coordinates clutch disengagement, shifting, engine speed and clutch engagement to accomplish smooth downshifts – just as a skilled driver would.
• Hill detection: Depending on gradient, down- or uphill, the A shift programs are modified to ensure optimum gear selection. In S mode, shift times are shortened so that the engine is always “on point” for best acceleration uphill, or engine braking downhill.
• Intuitive shifts: In the A mode under certain circumstances, DRIVELOGIC modifies downshifts. In cornering, uphill driving or braking, for instance, a downshift will occur sooner than if the car were simply being driven steadily on level ground. This feature can seem almost supernatural in vigorous driving on a winding, hilly road: SMG seems to read the driver’s mind, magically getting into the right gear before accelerating out of a corner.
• Grade assist: A “hillholder” function, active in both S and A modes. When stopped facing uphill, the driver actuates the left shift paddle. DRIVELOGIC “revs” the engine to about 1500 rpm and slips the clutch so that the vehicle does not roll back. This is available for brief periods only.
• Illuminated upshift indicator: The same orange LEDs that adjust the tachometer warning zone according to engine temperature help indicate to the driver when to upshift. Illuminating in 500-rpm segments, they light progressively as the engine approaches its redline (8000 rpm); given the M3’s catapult-like acceleration, this can be an appreciated assistance.
Since the introduction of the BMW M SMG system with DRIVELOGIC, BMW has introduced a less elaborate SMG version, with only two selectable shift programs within each of its automated and sequential modes; this system is now available in the 3, 5, and Z4 Series and will also be available in the upcoming 6 Series.
Chronicle of an SMG shift. To those versed in driving with a manual transmission, shifting comes naturally – one is hardly aware of letting up on the accelerator, depressing the clutch pedal, moving the shift lever, giving gas again and letting up on the clutch – all in coordinated sequence. SMG does all of this for the driver – and under hard-and-fast driving conditions does it more quickly than even the most skillful driver is likely to do. Here’s the operating sequence:
1. Via a position sensor, the control system always “knows” which gear is currently engaged.
2. When the driver signals a shift, the system selects the appropriate valves.
3. Hydraulic fluid at high pressure (1200 psi or more) disengages the clutch.
4. The M3’s six individual, electronically controlled throttles are closed.
5. Hydraulic cylinders move the transmission’s gearsets into the next gear.
6. If it’s a downshift, the engine is “revved” to the speed it will reach when the selected lower gear is engaged (the “double-clutch” function).
6. The clutch is re-engaged.
7. The throttles are opened again.
All this occurs – perfectly choreographed and calibrated to the vehicle speed, what the driver is doing with the accelerator pedal, the shift program selected and other factors mentioned earlier – in an interval that may be leisurely or a mere blink of the eye. The driver keeps a firm foot on the accelerator; SMG and DRIVELOGIC do all the work. Many enthusiastic drivers are fascinated by the way SMG works.
“Those same track enthusiasts,” noted Road & Track of drivers who enjoy driving on a race track in a March ’03 comparison test, “might also like the lightning-quick shifts of the SMG transmission. With paddle-actuated shifts performed faster than any human could do, the Formula 1-derived system takes some of the thinking out of driving fast. Do-it-yourself stalwarts may still prefer the satisfaction of performing their own gearchanges, but there’s no denying the system’s speed and convenience at the track."