You move eastbound on Interstate 195 into the deepening purple haze of the South Florida dusk. Training your roundel on a shimmering Miami Beach skyline, you downshift to third gear and dump the throttle. The tach needle whips around 6500 rpm; an unrestricted, free-flow exhaust roars obscenely as a thrumming mechanical whirr uncoils from the engine bay like a striking snake. Shift up, watch the needle whip past 7500 this time. You lift, skipping fifth to ease it into sixth, and the whirlwind of sound and acceleration abruptly dissipates as though it never happened.

Without warning a pair of triangular HIDs dives into view over your left shoulder, closing rapidly. In the mirror you glimpse a low, wedge-like shape advancing on your flank like some blood-crazed predator. The failing light flashes off a metallic neon sheen.

No worries. You're behind the wheel of Active Autowerke's supercharged M3 prototype. You blip the throttle, knock it back to fourth, and get back on the floor. Turns out you were in the mood for a little Italian.

Force-fed Active Autowerke BMWs have been prowling the streets of Miami and hunting the indigenous exotics since company founders Karl and Mike Hugh began officially turning wrenches under the Active name back in 1981. It's been nearly 30 years, but the dedication to ultimate BMW performance remains.

This, the company's new-generation supercharger kit for the E90-series M3, is still in its prototype stage, meaning it's so far the only one of its kind currently installed on a running vehicle. Everything you see under the hood here is basically a hand-fabricated one-off. Don't expect the end product to be so Mad Max in its presentation; the production version will be visually much closer to something you might see come from the factory.

It's formed around a custom HKS GTS8550 blower developed to Active Autowerke spec. In fact, the compressor remains pretty much a prototype in and of itself. (One other identical unit does exist and currently resides in an undisclosed location.) Having traditionally employed hardware sourced from Europe, Active looked further east for this latest go-around. The decision was a matter of volume, sourcing a larger capacity blower that would work with the confines of the engine bay.

"There were limitations as far as spinning the revolutions to get the airflow we needed to make the power we wanted from the V8," says Karl. "We needed something with more headroom." HKS out of Fujinomiya, Japan, answered the call with a supercharger that met requirements for output and efficiency as well as reliability. Active has successfully tested a similar blower on another shop car for more than 20,000 miles.

The E9X supercharger kit is for all intents and purposes 99 percent complete in terms of operation and performance. Mass producing and packaging the final production parts is next, in anticipation of an official release nearer this October. The complete kit will be all-encompassing: compressor and self-contained oiling system, belt tensioners, plumbing, an integrated airbox for the filter element, fuel enrichment parameters including high-volume pump and injectors, intercooler, provisions for relocating the oil cooler.

Because of the heat soak involved with boosting the S65 V8, running the blower without provisions for an intercooler was not an option. They chose a front-mount air-to-air unit for maximum airflow to both the I/C and the radiator. "The intercooler is capable of supporting 850 hp. Overkill," Hugh says. "But that's good; we can pull back-to-back dyno runs without any heat soak issues. High efficiency, zero maintenance... a win-win for us." Reportedly it all fits with only minor trimming of the front bumper and radiator supports.

It took four months to get the hardware to spec, a little bit longer to come up with the software, a task that Active Autowerke performs internally. Importantly, the new code will be flashed directly to the ECU. Once the big hope for cramming software tuning through increasingly complex factory code, the ubiquitous piggyback units have fallen back out of favor. The next generation of BMW software will supposedly monitor for these types of add-ons and send any perceived offenders slithering home in limp mode. ECU flashing, for those who can unravel the code, is back on the table as the only truly viable option.

Hugh welcomes the challenge. "If we're going to tune like the factory, we go through the ECU," he says. "Eventually, the piggybacks won't be able to do what the ECU will. It will separate the men from the boys for sure."

As with previous Active Autowerke supercharger systems, this one will be offered in two flavors: Level 1 and Level 2. The first will boost engine output by some 37-38 percent, about 570 hp. The second adds more aggressive boost, fueling, and a methanol/water injection system for total output of 638 hp and 460 lb-ft of torque, mathematically corrected for a reading at the crank. Max torque is up more than 50 percent over stock with increased output in front of the peak, or "beneath the curve" as they say. After peak, torque tends to simply level off in a relatively straight line as boost increases, the boost essentially "propping up" the torque curve.

Still, Hugh says: "This engine is about revs and horsepower. You have to keep it buzzing to see the true benefit. This supercharger is perfectly matched to its power characteristics. This thing pulls very strong right up to the 8400-rpm limit; it almost feels like it needs a higher one. The power curve looks like a staircase."

In addition to the blower setup, the prototype car wears standard Active Autowerke "Signature" series hardware, including a short-shift assembly to tighten gear selection, and a full exhaust from the headers back.

Running gear is comprised of a set of 19-inch BBS CH wheels shod with Michelin PS2 rubber. The chassis crouches over this rolling stock courtesy of another Active-recommended treatment, KW Variant 3 coilovers. These use electronic sending units in the front and rear to essentially simulate the electronically adjustable EDC sensors from the OEM dampers. They offer a wider range of manual suspension adjustment--14-way compression damping, "infinitely adjustable" rebound, and individual height adjustment. The suspension will be shortly upgraded to a KW Clubsport package for further on-track thrashing.

Depending on the time of day and your location in the city, Miami can be one of the more frustrating places on Earth to drive. At length you reach the water and make a crawl up the virtual parking lot that is Ocean Drive. You probably couldn't get any further from the M3's natural alpine habitat, but if you want to be seen (or heard), this is the place to be.

You goose the throttle; the exhaust report shivers off caf windows lining the seething beachfront sidewalk. Heads whip around; a coffee cup shatters against the pavement.

Yeah, the Active prototype'll do that too.

Active Autowerke E90 M3
supercharged prototype

* Layout
Longitudinal front engine, rear-wheel drive

* Engine
4.0-liter V8, dohc, 32-valve. Active Autowerke prototype intercooled supercharger kit and software, AA Signature exhaust

* Transmission
Six-speed manual, AA short shift kit

* Suspension
KW Clubsport coilovers

* Brakes
Factory assemblies

* Wheels and Tires
BBS CH, 9.5x19 (f), 10x19 (r)Michelin Pilot Sport 2, 255/30 (f), 275/30 (r)

* Exterior
Active Autowerke Signature badge

Peak Power: 638 hpPeak Torque: 460 lb-ft*AA data, corrected for crank

Keeping Active
Making a living playing with powerActive Autowerke has been officially making BMWs go faster since brothers Mike and Karl Hugh founded the company in 1981. But in fact the two were making BMWs go faster even before that. As Karl says, he picked up a '72 2002tii and "got hooked." Then came an E21 320i turbocharged for a 55 percent increase in power, and it wasn't long until they decided to turn the hobby into a business. The fledgling company soon became the largest independent BMW service center in all of Florida, with a sophisticated equipment arsenal and certifications from leading industry suppliers.

By 1995, Karl, a graduate from the University of Miami's School of Engineering (specializing in the internal combustion engine), had re-focused on the company's true roots: the thrill of turning fast BMWs into faster BMWs. In time Active Autowerke drew down its service support and today focuses exclusively on improving performance. While the bulk of business is conducted largely through mail order and a worldwide distributor network that serves nine foreign countries (including Germany), the company's on-site installation facility still stays busy. The day we visited, the shop floor featured pretty much standing room only.

Known originally for its turbocharged applications, today Active deals with supercharging as its main means for boosting power for a variety of reasons, cost efficiency and reliability chief among them. In addition to its signature supercharger packages, the company offers an array of proprietary performance upgrades like anti-roll bars, shift kits, pulley systems and brake upgrades, as well as supplying goods from respected aftermarket sources like KW Suspensions, BBS, and BMW Motorsport to name just a few. Services run the gamut from basic bolt-on upgrades to full racecar prep.

Active Autowerke also avidly supports and participates in BMW enthusiast and motorsport events. As this story goes to press, an Active Autowerke-prepped E46 M3 driven by Catesby Jones finished first in class and third overall in the 2009 One Lap of America (out of a field of more than 60 cars), while the prototype E90 began its long journey back from California's spring Bimmerfest. --KF

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