BMW AG marks the fourth generation of its M3 sports car with the model’s first fitment of a V-8 and hybrid-derived technology.

Designed by the auto maker’s M GmbH performance unit and based on a die-cast aluminum/silicon block produced at its foundry in Landshut, Germany – which also manufactures engine blocks for the BMW Sauber Formula 1 team – the new 4.0L DOHC V-8 will power the ’08 M3 when it formally debuts in production form at the Frankfurt auto show later this year.

BMW’s release this week of the engine’s technical specifications quells months of speculation about the future of the M brand’s most performance-oriented car.

The new mill, which shares much of its layout with the 500-hp 5.0L V-10 found in the M5 sedan and M6 coupe, is rated at 420 hp at a lofty 8,300 rpm and 295 lb.-ft. (400 Nm) of torque at 3,900 rpm, the auto maker says, noting 85% of maximum torque is available from 2,000-6,500 rpm.

And in an effort to reduce parasitic losses stemming from energy-sapping ancillaries, BMW has fitted the V-8 with a regenerative braking system called Brake Energy Regeneration (BER).

Using an absorbent glass-mat battery, which can withstand a greater load than a conventional lead-acid unit, the BER system charges the car’s battery when under load without activating the alternator and tapping into the engine’s power supply. This on-demand generation of electricity reduces fuel consumption, while also allowing all 420 hp to be available for acceleration, BMW says.

Further aiding BMW’s “M high-speed engine concept,” while also allowing for the use of lighter drivetrain components and shorter transmission ratios, is the lightweight construction of the new engine.

Tipping the scales at 445 lbs. (202 kg), the V-8 is some 33 lbs. (15 kg) lighter than the outgoing model’s 3.2L DOHC I-6, which only made 333 hp.

A lightweight-alloy block, which houses a forged steel crankshaft and features a high-strength bedplate design for improved rigidity, forms the basis for the 90-degree V-8 and forgoes conventional iron cylinder liners in favor of cylinder bores coated with hard silicon crystals.

Iron-coated aluminum pistons are cooled from below by high-pressure oil nozzles and contribute to improved durability and a 12:1 compression ratio. Connecting rods are of a high-strength steel and magnesium alloy.

Cylinder heads with four valves per cylinder also are made of aluminum and feature efficient cross-flow cooling and a low-pressure version of BMW’s double-VANOS variable valve timing technology.

Unlike the V-10’s high-pressure system, the low-pressure VANOS configuration operates under regular engine oil pressure, allowing for better optimization of camshaft adjustments without the need of a separate high-pressure oiling system, BMW says.

To improve responsiveness, a lightweight composite intake manifold sports electronic throttle control and eight individual butterflies positioned close to the intake valves.

Of note is BMW’s use of conventional port fuel injection to attain an impressive 105 hp/L. Audi AG’s RS4 sedan, the M3’s primary competitor, utilizes direct gasoline injection to produce a similar 420 hp (at 7,800 rpm) from a larger 4.2L V-8.

In addition, the M3’s V-8 utilizes a conventional wet-sump oiling system (rather than a race-worthy dry sump system) optimized to handle lateral and longitudinal forces of up to 1.4 g – far greater than the cornering forces the M3 likely will generate. The system features two oil sumps, a small one near the front of the engine and a larger one toward the back, with a separate re-flow pump continuously transferring engine oil fore to aft.

Under power, spent gases are routed through 4-in-1 fan-type exhaust manifolds with close-coupled catalytic converters. Lightweight, thin-wall stainless steel tubing, two more catalysts and a single, large silencer make up the rest of the M3’s exhaust system, which assist the engine in meeting Euro 4 and U.S. LEV 2 emission standards.

Other highlights include an engine knock-detection system, which uses the spark plugs to monitor and assist in the control of ignition for optimized combustion, and a new MS660 engine management system.

Designed as an evolution of the 5.0L V-10’s system, the MS660 coordinates the engine with all the other control units in the car, including those for the clutch, transmission, steering, brakes and Dynamic Stability Control.

In addition, the engine management system allows for the M3’s adoption of the V-10’s Power Button feature, which, when activated, changes the engine’s power output from normal to high-performance modes (a boost from 400 hp to 500 hp in the M5).

BMW has yet to say what the performance difference will be in the M3.

Transmission choices for the M3 likely will include a 6-speed manual and a 7-speed SMG (Sequential Manual Gearbox) unit. The auto maker plans to release that information, along with additional details about the car, early next month prior to the New York auto show.

msutton@wardsauto.com