Driving the Alpina B10 BiTurbo, The World's Fastest Four-Door in 1991

The BMW-based twin-turbo machine did 180 mph in 1991, putting it on equal footing with the wildest cars from Ferrari and Lamborghini.

Brendan McAleer

To the average bystander, it's just a BMW 5-series. E34-chassis, four round headlights, twin kidney grilles, and a silhouette well balanced between greenhouse and sheetmetal. It's a classic from the era when Bimmers had an air of elegance to them. But this is no BMW. It's a weapon.

At the top of a mountain, a collector-plated Honda VF 750 Interceptor curls in to get a closer look at a forest-green sedan. The rider pops his visor open.

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“Please tell me you're selling it,” he says.

“You know what it is?” Sean Douglas, the car's owner, responds in surprise.

“Oh yeah,” comes the reply. “I know exactly what that is.”

Brendan McAleer

The rear spoiler, front airdam, and wide, multi-spoke wheels have an air of M5 about them, but it's not an M5. In fact, when new, this car sold for just under twice the price of BMW's hottest 5er. It looks like a BMW, but it's actually an Alpina, a B10 BiTurbo. In 1991, that meant it was fast enough to place it in company like the Ferrari F40, the Lamborghini Diablo, and the RUF Porsche TR2 in a followup to Road & Track's world's fastest cars shootout. The B10 went 180 mph, making it the fastest four-door machine in the world at the time, and R&T's Belgian-born European Editor, the late Paul Frère, fell head over heels.

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“For me,” he said, “this is the car. I think this is the best four-door in the world.”

For a workaday executive saloon to impress a former 24 Hours of Le Mans champion is no mean feat. Then again, Frère was already intimately familiar with Alpina's work, having driven one of their race-prepped BMW 2002s. With it, he was able to set lap times besting a contemporary Porsche 911S.

Brendan McAleer
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Alpina began by suppling performance upgrades like carburetors and camshafts. Formerly a typewriter manufacturer, the Buchloe-based company moved into motorsport under the direction of scion Burkard Bovensiepen.

Brendan McAleer

BMW, impressed by the quality of the fettling work done on the 1500, turned to Alpina for early motorsports efforts. Both James Hunt and Niki Lauda would become drivers for the Alpina team, and the brand soon rose to prominence with trophies in endurance and touring car racing. Our own Sam Smith drove an Alpina-prepared 2002 at the Monterey Historics not long ago, calling it “unbridled German mini-hell. With backfires.”

Brendan McAleer

But the Alpina B10 Biturbo is no harsh-riding racing machine. Instead, it follows in the footsteps of other road-going Alpinas, all of which seemed to herald the near-future of BMW. In 1978, Alpina was first to put a BMW straight-six into a 3-series. They also built a boulevard strafer out of the first, E12-chassis 5-series, seven years before the M5. In its way, the B10 presaged BMW's twin-turbocharged future: Effortlessly fast sedans built to set the autobahn aflame.

Between 1989 and 1994, Alpina built just 507 of these machines. The base for the car was the 535i, which arrived in Buchloe to be totally transformed. BMW's original VIN was struck out, replaced with one from Alpina. The engine was completely disassembled and rebalanced, with forged pistons, remachined combustion chambers, a new camshaft, and unique intake and exhaust manifolds. Twin Garrett T25 turbochargers provide a maximum of 11.4 psi of pressure, with boost levels controllable via a dial marked “Ladedruck” just ahead of the shifter.

Brendan McAleer

Total power output is 360 hp at 6000 rpm, and 384 lb-ft of torque at 4000 rpm. Some 90 percent of that torque is already available by just 2500 rpm, enough to lunch the standard 535i gearbox; it's replaced by a Getrag 5-speed unit and a high-friction Fichtel & Sachs clutch.

Next, Alpina prepared the B10 for speed. The suspension was reworked and stiffened to provide confidence at max-velocity, including a rear load-leveling suspension that firms up to prevent excessive rear camber north of 170 mph. The spoiler and airdam are functional, and the B10 hunkers low over its 17” wheels, 8.5” wide up front an 9.5” wide out back. Through the standing half-mile, the B10 was quicker than contemporaries like the Ferrari 348, Porsche Carrera 2, or Acura NSX. But these were not really the competition.

Brendan McAleer
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Instead, the B10 was designed as a grand tourer without peer, something with which to dispatch AMGs as if they were parked. Our conversation with the VF rider concluded, Sean and I climb back into his car, crank the ladedruck all the way to the right, and hammer down the mountain.

The B10 handles like an avalanche. Speed builds instantly on a wave of creamy-smooth torque. The view out the front and the feel of the steering wheel in your hands is pure old-school BMW, but the engine might have been lifted out of a modern 540i. The characteristic idling basso profundo burble of a large displacement straight-six disappears under throttle, replaced by the woosh of air being rapidly ingested by the twin turbochargers.

The speedometer moves like a watch hand in fast forward. There's an initial leap at the throttle—with little to no turbo lag—and then a freight train pull to limits only suitable to the derestricted autobahn. What's missing is the drama. Where an M5 brings a mechanical scream and the desire to shred corners, the B10 is more a gentleman's tourer. The buyer who owned one of these might also have a Ferrari for play. The Alpina was built to exchange fuel for time, hurrying hard across Germany's smooth roadways at warp speeds. It's a Concorde with a manual gearbox.

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Brendan McAleer

The original owner ordered this B10 with plain seats and no exterior stripes. It has a few odd options (power headrests, for instance), but overall it's configured to fly beneath the radar. Douglas, the current owner, reapplied the iconic Alpina striping, and does much of his own work on the car. An engineer by training, he's had to resolder various parts of the instrumentation, and just finished a comprehensive by-hand cleanse of the fuel system.

Brendan McAleer

To Douglas, the B10 represents the realization of a dream. Reading Frère's words all those years ago inspired him to keep the original R&T article. Ten years ago, he got the chance to put the actual car in his garage, at a price far more reasonable than the exotics it ran with. It's not an easy machine to own, but for enthusiasts willing to get their hands dirty, the Alpina B10 is something very special indeed.

Not everyone knows what it is, of course. However, those who do are often green with envy.

Brendan McAleer
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