2008 BMW M3

Don Sherman
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2008 BMW M3

Never mind that the confrontation is a year away; the shooters are already vying for high ground. Knife fighters know better than to show up at this bazooka battle. Contenders armed with anything less than a hot V-8 will be blown to smithereens.

Audi made that clear by rolling out its direct-injected 4.2-liter RS4 packing 420 hp. Lexus is finally mounting a serious challenge with the upcoming "more-than-400-hp" IS-F sport sedan. Mercedes-Benz recently retired its C55 AMG to clear the decks for a new C63, scheduled to bow later this year. Cadillac's second-generation CTS-V, powered by a strapping 6.2-liter V-8, is due next year.

That leaves BMW. Twenty years ago, when this brand mustered the gumption to offer a sport coupe equally at home on road or racetrack, a tide of elation washed over every car enthusiast in the land. Two years ago, the buzz about a new M3 with V-8 power began.

Those who worship the Bimmer bible saw it in the scriptures. The second-generation E36 upped the cylinder count from the original four to six in the early 1990s. A displacement boost from 3.0 to 3.2 liters arrived for 1996. BMW's M department began shipping its incendiary S54 six--333 hp, 8000-rpm redline--in the third-generation E46 M3, launched in 2001. It didn't take a prophet to deduce that the E92 coupe, which rolled forth last fall with a muscular twin-turbo six under its hood, was also engineered to host a V-8.

At the Geneva show, BMW finally ac-knowledged what everyone already knew by presenting a supposedly conceptual M3 and hints about its engine. The new 4.0-liter V-8 is a derivative of the remarkable 5.0-liter V-10 that powers today's M5 and M6. Both powerplants share an architecture that includes aluminum-block-and-head construction, a 90-degree V-angle, a 3.6-inch (92-mm) bore, a 3.0-inch (75-mm) stroke, 3.9-inch (98-mm) bore spacing, and a 12.0:1 compression ratio.

Like the V-10, the new V-8 block is a low-pressure die casting made of an aluminum alloy with a high silicon content. The lowly Chevrolet Vega used the same material thirty-six years ago for the same reasons that BMW selected this approach. The weight and complexity of iron cylinder liners are avoided because silicon is sufficiently tough to serve as the bore surface. A honing procedure polishes the hard silicon crystals that precipitate out of the molten aluminum during casting. To improve the wear resistance of the oil-cooled, cast-aluminum pistons, their skirts are plated with a thin coating of iron.

The V-8 block's bottom is reinforced by a stiff aluminum and iron bedplate that keeps the forged-steel crankshaft happy at its work. Under that, there's a dual-sump oil pan straddling the car's steering and structural components. An extra pump transfers lubricant from the front reservoir to the main storage sump at the rear, where the oil is sucked up to serve as the engine's lifeblood with no loss of pressure when the driver flings the M3 through the inevitable high-g maneuvers.

Cylinder heads embody Formula 1 practices, in no small part the result of BMW's team-ownership role in top-echelon motorsports. Two chain-driven hollow camshafts bear directly against the hydraulic bucket-type tappets that open four valves per cylinder. Computer-controlled drive mechanisms vary intake and exhaust event timing on cue to optimize smoothness, output, and combustion efficiency over the full operating range. Each pair of short, straight intake ports is fed by one fuel injector, one close-coupled servo-activated throttle, and a molded-plastic air trumpet.

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