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BMW’s M3 Adds Power and Pistons

The engine in the 2008 BMW M3 puts the longstanding inline six-cylinder to rest and replaces it with a lightweight 4.0-liter V8.

The engine in the 2008 BMW M3 puts the longstanding inline six-cylinder to rest and replaces it with a lightweight 4.0-liter V8. Like the V10 in the M5, the new engine displaces 500 cc per cylinder, comes from the same Landshut, Germany, foundry that builds BMW’s F1 motors, has a crankcase made of an aluminum silicon alloy, and iron-coated pistons that run in the uncoated honed cylinder bores.

At 445 lb., the 4.0-liter engine is 33-lb. lighter than the 3.2-liter inline six it replaces. The six developed 343 hp (107 hp/liter); the new motor produces a stout 420 hp (105 hp/liter) right out of the box. It’s doubtful that any power increase will come from spinning the engine faster as it already has a maximum engine speed of 8,300 rpm, and produces 295 lb-ft of torque—251 lb-ft is available from 2,000 rpm and 85% of maximum torque is available over a 6,500 rpm range—at a reasonable 3,900 rpm.

The double-VANOS camshaft timing system has been revised to work with normal oil pressure, even at the 8,300 rpm rev limit. That oil is supplied via twin oil pumps capable of keeping the wet-sump engine lubricated at 1.4 g, with a separate re-flow pump that pulls oil from the front pump and pumps it to the larger pump at the rear, when necessary. Meanwhile, air enters the engine through eight electronically controlled throttle butterflies. These are located very close to the intake valves, and sit at the bottom of a composite intake manifold. Finally, the stainless steel exhaust manifolds are hydroformed, which gives them walls just 0.65 mm to 1.0 mm thick.

Surprisingly, the M3 V8 also makes use of regenerative braking to charge the battery. An absorbent glass mat battery is designed to handle the greater number of charging cycles and intelligent control of the alternator means it is disconnected when the engine runs under load. This not only increases fuel economy, but makes more drive power available under acceleration.—CAS