BMW is plotting a return to the high-end sports car market with a dramatically styled coupe and roadster aimed at providing the German carmaker with a rival to the hugely successful Mercedes-Benz SL.

Dubbed Z6, Munich’s latest flagship sports car is conceived as a follow-up to the high-priced and ultra-low-volume Z8, which saw production of just 5703 cars between 1999 and 2003. Z6 will be priced below the $130,000 Z8, and insiders say it will be produced in “considerable volumes.” The car will be built in Germany and will be a high-tech showcase for many of BMW’s latest innovations.

“It is not just a flash in the pan,” a source told AutoWeek at the launch of the Z4 M Coupe. “We’re looking at establishing a whole new model line.”

At least one full-size model of the new car reportedly exists at BMW’s research and development center in Munich, though the final design is still up in the air. The car will form part of a rumored three-strong Z-car lineup including a new entry-level Z2 and a successor to today’s Z4.

The two-seater is already developed to an advanced stage and enjoys strong support from the BMW board.

“A go-ahead is likely, provided BMW can find the necessary engineering capacity,” said the source.

Z6 will be about the same size as the existing 6 Series and will borrow mechanical components from both the 6 Series and the 5 Series. But while the 6 Series was conceived as a luxurious 2+2 GT, the Z6 is envisioned as a pure sports car.

Original reports suggested the Z6 may boast a mid-engine design, but BMW appears to have settled on a traditional front-engine format. The aim, according to one high-ranking insider, is to create a car that combines BMW’s traditional strengths of top-level performance, handling and quality with a raft of new innovations, including lightweight construction to provide it with strong levels of performance but also class-leading levels of economy and low-emission levels.

Keen to avoid the criticism leveled at the Z8, with a design influenced by BMW’s legendary 507, the Z6 boasts a contemporary design with cues from the Z4. The highlight of the new sports car is its high-tech structure—a combination of aluminum space frame and steel unibody construction. BMW is planning to take this technique, pioneered on the 5 Series and 6 Series, one step further in a move aimed at bringing the Z6 to market at less than 3300 pounds.

Rather than using aluminum for the front end only, engineers are investigating using the material for the middle section as well. This should help to achieve a desired 50:50 front-to-rear weight distribution.

Unlike the Z8, which was sold exclusively with a 5.0-liter, 400-hp V8, Z6 will come with a range of engines. Sources suggest the lineup will likely kick off with the new 3.0-liter, twin-turbocharged inline six-cylinder, with a range-topping version packing Munich’s secret 4.4-liter, twin-turbocharged V8 and an updated version of the M5’s 5.0-liter V10.

Channeling drive to the rear wheels will be a new double-clutch sequential

manual gearbox.

with a range-topping version packing Munich’s secret 4.4-liter, twin-turbocharged V8

Will BMW's Z4 become a Z6? The Bavarian car maker is about to develop a replacement for the current Z4 sports model, which has been on the market since fall 2002. According to spy photographer and insider Hans G. Lehmann, the all new successor to the Z4 is schedule for release in September 2009.

No prototypes have been sighted on the roads yet, just some speculations and a possible name change into "Z6" are in the air. Furthermore talk is that the new coupe will adapt the engines from the new BMW 3-Series Coupe.

Spy photographers caught an unusual BMW test mule in transit from the company test track to BMW headquarters in Munich. Given the size and the wheelbase in play here, this is very likely to be the first serious test bed for the next-generation Z8 — BMW's upcoming Mercedes SL fighter. It's not known if the car will be called Z6, Z8, or Z10.

BMW has used this disturbingly unique mule construction method before, circling the Nürburgring about 18-months-ago in another, larger, high-performance-bread-van-looking concoction. That mule was most likely an early testbed for the X6, which has recently come to fruition as a real vehicle clearly in BMW's new model pipeline.

Despite their rough, agricultural appearances, sources say these test mules are very advanced chassis development platforms. Different dynamic set-ups are said to be much easier to achieve than on more traditional mules, and this rough-hewn architecture reportedly allows for more convenient, and more detailed vehicle performance analysis.

If past timing holds true, we expect to see more evolved Z8 prototypes (actually approximating the proportions and design of the final car) to break cover in the next 12-to-18-months.