Mercedes-Benz expands its ultra-high-performance range of track-ready cars with the unveiling of the ’09 SL65 AMG Black Series coupe.

Built upon the already-formidable SL65 convertible and following in the tire treads of the recent CLK and SLK Black Series models, the limited-edition SL boasts numerous dynamic and weight-saving improvements geared toward making the luxury roadster a proper sports car.

As the standard SL65’s 6.0L twin-turbocharged SOHC V-12 already makes a mountainous 604 hp, large amounts of extra thrust were not needed.

However, new turbochargers (12% larger), wastegates and revised intake plumbing, along with a more-efficient intercooler (30% larger) and free-flowing exhaust, improve throttle response and boost output in the Black Series to 670 hp at 5,400 rpm.

Maximum torque remains electronically limited at 738 lb.-ft. (1,000 Nm) between 2,200 rpm and 4,200 rpm for transmission durability, but the auto maker says the engine is capable of 885 lb.-ft. (1,200 Nm) when unrestricted.

Mercedes’ adorns the standard 5-speed, paddle-shifted automatic transmission with its new SpeedShift Plus technology, which debuted on the ’08 SL63 AMG and employs a lock-up clutch in place of a conventional torque converter for improved shift response. Included in the gearbox’s programming are comfort, sport and two manual-shift modes (M1 and M2), the latter spitting out 25% quicker shifts than the first.

To achieve the 3.8-second 0-60 mph (97 km/h) time and electronically-limited, 198-mph (320 km/h) top speed of which Mercedes says the SL65 Black Series is capable, the car was put on a strict diet of carbon-fiber-reinforced plastic (CFRP).

A curb weight of 4,123 lbs. (1,870 kg) is some 551 lbs. (250 kg) lighter than the standard roadster and is a result of using CFRP for the vented nose, tail, hood, trunk and swollen front fenders.

The broad-shouldered look is menacing, particularly with the rear spoiler deployed at speeds above 75 mph (120 km/h).

Further reducing mass, as well as lowering the center of gravity and improving aerodynamics, is the deletion of the SL folding hardtop. In its place resides a fixed CFRP roof shell with integrated rollover protection, a larger rear window and sleeker roofline.

In addition, a broad, carbon-fiber splitter graces the leading edge of the front fascia, while an integrated diffuser channels air out back and conceals the cooling system for the new locking differential.

As all Black Series cars are designed for track-day use, the SL65’s standard Active Body Control air suspension is ditched in favor of an adjustable coil-over setup with variable settings for rebound, compression, ride height and camber. Lightweight aluminum wheel carries also are included, as are revised spring links, camber struts and steering hardware.

Overall wheel track is about 3.9 ins. (10 cm) wider in the front and 3.5 ins. (9 cm) greater in the rear, with staggered 19-in. front and 20-in. rear twin-6-spoke AMG wheels providing an even more stable footprint.

Other go-fast novelties include an 8% more-direct steering ratio and 3-stage electronic stability control with standard, sport and off settings.

Countering the SL65 Black Series’ acceleration is Mercedes’ largest-ever carbon-ceramic disc-brake package: 15.4-in. (39-cm), 6-piston units up front and 14.2-in. (36-cm), 4-piston units out back.

The interior can be had in any color as long as it’s black, the auto maker says, and is largely unchanged from the standard car, save for CFRP-shelled sport seats, a smaller performance steering wheel and various bits of carbon-fiber trim.

The new speedometer counts up to 225 mph (362 km/h) over a black background, while the contrasting white-faced tachometer sports four integrated-LED shift lights.

Although Mercedes won’t yet say what the price of entry is for the new car, various reports peg the figure north of $300,000, far exceeding the standard SL65’s $191,575 sticker, yet well below the SLR McLaren’s near-$500,000 fee.

Ensuring the exclusivity of the SL65 Black Series, less than 350 examples will be produced at Mercedes-AMG GmbH’s factory in Affalterbach, Germany, with about 200 units making their way to the U.S. beginning late this year.

msutton@wardsauto.com