4/1/2008 | 7 MINUTE READ


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After building a number of edgy versions of the M3, BMW rethinks the formula to create a high-performance 3 Series with supercar performance and everyday usability.


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What happens when you redesign 80% of a car that has been on the
market for less than two years, leaving only the glass, doors, trunk lid, lights, and load bearing structure in common with the latest variant? For many companies, bankruptcy is the next step in this progression. For BMW, it's just a step in the creation of the latest version of the M3. "Often, this is the only car in the household," says Larry Koch, M Brand manager, BMW North America, "so we had to make it usable." In truth, all M3s since the first E30-based version back in 1986-a car created so that BMW could build the 5,000 road versions required to race in the German Touring Car Championship-have been usable. They just haven't always been enjoyable off the track, a point punctuated by the first M3 with its 192-hp inline four-cylinder, and the last version with its 333-hp inline six-cylinder. Both have the high-strung edginess of a methamphetamine addict.

That wouldn't do for the latest version, especially with cars like the V8-powered Lexus IS-F moving into the M3's territory. So BMW borrowed 4/5ths of the 5.0-liter V10 found under the hood of the larger M5, mated it to Getrag-sourced gearboxes (a six-speed manual with a dual-plate clutch from the M5, or a new seven-speed dual-clutch semi-automatic), and built the resulting car around this powertrain. "The V8 produces 414 hp at 8,300 rpm," says Bernd Limmer, Technical Director, M3, "with 295 lb-ft of torque-85% of which is available from 1,800 to 8,300 rpm-at 3,900 rpm." The engine features an aluminum-silicon compound crankcase, iron-coated pistons running in uncoated honed cylinder bores, bedplate construc-tion, eight individual throttles, twin oil pumps capable of keeping the engine lubricated at 1.4 g, and hydroformed stainless steel exhaust manifolds. It also weighs 445 lb., which is 33 lb. less than the last M3's 3.2-liter inline six-cylinder engine.

"We followed a simple formula to keep the wheel torque at an optimal level," says Limmer. That equation, Mdrad = iges x Mdmot, states that wheel torque = axle ratio x engine torque, and "resulted in a high rear axle ratio (3.846:1) matched to the engine output for the greatest acceleration off the corners," he says. To match that performance BMW specified cross-drilled compound brake discs and floating calipers for the best braking performance. "Ceramic brakes are a disadvantage on the road," says Limmer, "because they can't produce sufficient heat in most cases to stop in the shortest distance possible." Yet conventional materials often fall apart on the track. To accommodate both requirements, BMW engineers specified a design where the brake disc and hat are separated by pins that allow the disc to float above the hat, leaving it free to expand and contract as temperatures rise and fall without introducing any vibration or warping. The discs are 14.2-in. x 1.2-in. in front and 13.8-in. x 0.94-in. in the rear. Both use single-piston swing calipers that rotate the caliper around its top mounting after removing a single lower bolt. This makes it possible to remove the brake pads without changing the relationship between the brake and disc, or putting strain on the brake piping. The M3 also makes use of regenerative braking during overrun and under braking. Unless there is a need for it to recharge the battery while the engine is under load, the alternator remains disengaged.

In addition to these changes, BMW completely rethought the suspension, saving only the rear longitudinal links from the standard-issue 3 Series. "We redesigned the thrust plate connection from the front struts to the front uprights, and triangulated the rear suspension from the lower outboard links forward to the body," says Limmer. "This cuts axle tramp and twist, and evens out the load on the suspension parts under extreme conditions." In addition, nearly all of the front axle components are now made of aluminum, as are the pieces for the five-link rear suspension. The latter includes forged control arms and aluminum dampers that contribute to a 5.5-lb. weight reduction. Electronic damping control adjusts the shocks only when there is a dynamic reason to increase damping forces, so that the ride stays comfortable for as long as possible. When activated, it makes the damper three to 12 times stiffer than normal, and works in concert with the hollow front and rear anti-roll bars to reduce roll in hard cornering.

The final drive uses what BMW calls "Variable M Differential Lock" to shift up to 100% of torque to the drive wheel with the best traction. Once wheel speeds equalize, however, the differential opens until the system recognizes a need for it to relock. According to BMW's Larry Koch: "This lock/unlock sequence is not only variable from 0% to 100%, it takes place about five times per second to ensure optimum traction on all surfaces." In the same vein, the optional Technology Package adds an "M Dynamic Mode" that lets the driver alter specific driving functions. These include the ability to choose from three levels of stability control (Auto, M Dynamic, and Off), three levels of damper control (Normal, Comfort, and Sport), three engine maps, and two levels of power steering response. Once set, the driver presses the "M Drive" button in the console to engage the system.

BMW engineers also added a carbon fiber roof to the M3 Coupe to cut 11 lb. from the highest point of the body and increase body rigidity. Finished in a clear paint, the panel is built at the company's Landshut, Germany, facility just north of Munich. In addition, the front fenders of all M3 models (Coupe, Sedan, Convertible) are thermoplastic; the hood is made from aluminum. Inside, BMW offers a number of trim options including woven leather that mimics the look of carbon fiber. "Each piece is hand-stitched and fitted to the trim piece that encompasses the air vents along the instrument panel," says Koch.



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