The International Motor Show in Frankfurt can be somewhat intimidating to O.E.s, tuners and aftermarket manufacturers. After all, it is the show where many new model vehicles and concept cars are first introduced to the masses, each subject to celebratory praise and unyielding criticism.
It can also be a great source of inspiration, which is how BMW and MINI Cooper tuner AC Schnitzer sees it. "We view Frankfurt as an opportunity, an invitation to show the world what AC Schnitzer is cable of," said company representative Michael Drawz. Never short of inspiration, ACS pulled its collective energies together and produced its most elaborate offering to date: a Z4 based concept coupe. Pushing the Z4 platform to its limits, the sports coupe, referred to as the V8 Topster, is ACS' tribute to BMW's performance M-line heritage, including a stylistic nod to the "fugly" M Coupe.
Following the concept's North American debut at the 2004 SEMA Show, european car was granted a day of drive time just prior to its return to ACS' corporate headquarters in Aachen, Germany. Arriving early in the morning at CEC (Clause Ettensburger Corp., the U.S. distributor for Schnitzer), I was introduced to both Michael Drawz and ACS technical manager and test-driver Manfred Wollgarten.
As the sun rose on what would be a typical warm Southern California November day, we jumped into the equally bright coupe and headed toward Malibu on the Pacific Coast Highway. Judging from the commotion caused by all the rubbernecking, one would have thought the car was piloted by a gorgeous movie star with an equally attractive passenger alongside. The V8 Topster even got a Z8 driver to raise an eyebrow in acknowledged approval.
While I admired the car visually, appreciating its unique appearance, what was under the slightly raised hood and beneath the floorboard was what made the most lasting impression. A jab at the throttle and the subsequent deep resonating growl immediately confirmed something big was hidden within. That something was a specially tuned version of BMW's 4941cc eight-cylinder M5 powerplant.
Developed as a one-off engine in close collaboration with BMW Works team Schnitzer Freilassing, the beastly unit produces an impressive 450 bhp at 6600 rpm and 383 lb-ft of torque at 4100 rpm. Featuring a 94x 89mm bore and stoke, the engine is equipped with special intake and exhaust camshafts. The cylinder heads have also been machined, the compression raised to 11.5:1 and the control unit reprogrammed. Because of the engine's physical size and placement within the bay, the oil sump and oil pump were modified and all oil lines were rerouted. Furthermore, engine airflow was optimized by way of new intake pipes and two air filter boxes. The wonderful rumbling exhaust note was due in part to a specially fabricated stainless-steel double exhaust system with a quad-pipe-tip configuration.
The engine's massive output is ideally mated to a six-speed M5 transmission with M3 axles. The widened rear axle features a 3.62:1 gear ratio as well as a variable differential lock from 0- to 100%, depending on load. An ACS short shift package was also included for quick and precise gear selection.
Since the car is capable of 0 to 62 mph in 4.5 sec, 0 to 124 in 13.9 sec. and a top speed of 189 mph, stopping power and chassis stabilization were also of paramount importance. Accordingly, the car is equipped with an ACS high-performance brake kit, which uses larger brake discs (365x32mm front and 328x20mm rear) in conjunction with special brake calipers (two-piston fronts and single-piston rears). Even under continuous hard braking, the system achieves deceleration values of more than 1 g.
The Topster's driving dynamics are nothing short of spectacular, thanks to a nine-position adjustable ACS racing suspension. As well as lowering the car by 35 mm, the spring and damper rates have been substantially modified for more aggressive performance. Front and rear ACS anti-roll kits and an upper aluminum strut brace further define the package.
In developing the tire-and-wheel combination, several factors came into play, including the need for additional traction to handle the power increase. A set of Michelin Pilot Sport Cups fit the bill, measuring 255/30 R20 and 305/25 R20 in the front and rear, respectively. The wide 9.0x20- and 11.0x20-in. ACS five-spoke wheels perfectly complement the tire selection and the car's overall appearance.