Alpina->ke1232 has a rich, 50-year history with BMW.->ke178 The pair have built some of the most impressive luxury and performance vehicles ever to roll off a German assembly line. Unlike aftermarket tuners that begin work with a finished production car, Alpina works directly with BMW inside its factories to build specialty vehicles for the most picky of customers. The pair’s latest products are diesel-powered 4 Series coupe->ke141 and convertible.->ke144 Starting with the bones of the 4 Series,->ke3834 Alpina juices up the 3.0-liter, bi-turbo, inline six-cylinder to make an impressive 350 horsepower and 516 pound-feet of torque. Sadly, the oil-burner is not available in U.S.-spec 4 Series BMWs. Those across the pond will enjoy the benefits of diesel, getting more than 44 mpg on the highway. The added grunt to this twin-turbo beast means sub five-second zero to 60 mph times.

Alpina didn’t just make the D4 Biturbo faster. Added to the running gear are auxiliary springs with thicker anti-roll bars and adjusted camber and toe-in settings for the Alpina-specific wheels and Michelin Super Sport summer tires. The car already makes use of electronically controlled dampers that give the driver adjustability in the suspension. BMW’s limited-slip differential helps put power to the ground.

Click past the jump for more on the BMW Alpina D4 Biturbo.

Exterior

Alpina does some careful reworking of the BMW 4 Series' exterior in order to differentiate itself. The most noticeable are the 19-inch Alpina Classic wheels. The 20-spoke design helps cut weight while a hub-mounted valve stem keeps the look consistent. A hollow-drilled spoke feeds the air into the wheel.

Up front is an added lower air dam that helps direct air flow into the radiator. Its Alpina block lettering also advertises the car. Out back, a specialized diffuser is molded around the quad exhaust pipes tipped in chrome. Owners have the option of choosing a standard paint color or choosing a more custom paint color through BMW Individual.

Exterior Dimensions

Interior

Alpina aims to please when the interior is concerned. The builder works with BMW Individual to help customize the cockpit to whatever specification wanted. Typically, Alpina cars have like-branded badging on the floor mats, seatbacks, steering wheel, and on the individualized and numbered plaque on each car. Alpina doorsill covers tell entering occupants of the car’s uniqueness.

The gauge cluster also gets a special treatment, fitted in a dark blue hue with red needles. Unless otherwise ordered, the steering wheel comes covered in Lavalina leather with Alpina-colored blue and green stitching.

Drivetrain

Here’s the best part. Aplina has tweaked the Euro-spec, 3.0-liter, turbo-diesel, inline six-cylinder to get an additional 37 horsepower and 52 pound-feet of torque, bringing the output numbers to 350 horsepower and 516 pound-feet of torque. Aplina did this by reducing pressure losses and adding a more free-flowing air intake system. A high-performance cooling system is also added, consisting of a large-volume intercooler and two radiators to keep temperatures down.

An eight-speed automatic transmission from ZF does the shifting. The car gets a unique torque converter and tailored software makes shifts come even quicker than usual. The typical three shifting modes translate over: Automatic Mode, Sport Mode, and Manual Mode.

This all adds up to a 0-to-62-mph sprint of 4.6 seconds in the coupe and five seconds with the extra heft of the drop top. Top speed checks in at 178 mph in the coupe model and 170 mph in the convertible.

Drivetrain Specifications

Suspension and Chassis

Alpina also works to make the 4 Series coupe and convertible handle better than stock. The summer performance tires mounted on lightweight wheels are the first line of offense. Thicker anti-roll bars keep the car flat through the corners and the standard BMW electronically adjustable dampers works to smooth out the suspension over rough roads while providing a firm ride on smoother surfaces.

Pricing

Pricing for the BMW Alpina D4 Biturbo starts at €58,600 (roughly $73,096 as of 12/02/2014) for the coupe and €64,800 (roughly $80,830 as of 12/02/2014) for the convertible. The price can quickly jump from there when ordering more custom exterior colors, interior leathers, or other bespoke parts.

Pricing Details

Competition

2015 Mercedes C 63 AMG

Similar to BMW’s relationship with Alpina, AMG is Mercedes’ performance division. The C 63 AMG is the badder version of the C-Class coupe. The AMG version comes powered with a 6.3-liter, gasoline-powered V-8 that makes 457 horsepower and 442 pound-feet of torque. A seven-speed, dual-clutch transmission does the shifting to the rear tires and an AMG-specific suspension makes the C 63 handle like a proper sports car. While the AMG hits 62 mph in 4.4 seconds, it doesn’t quite match the diesel BMW’s fuel efficiency, earning only 28 mpg on the highway.

The C 63 AMG Coupe starts at $65,625.

2014 Audi RS5

Though not tied to a performance group like Alpina or AMG, the letters "RS" mean a lot for Audi. In this case, the RS5 means the docile A5 coupe gets reworked into a back-road-burning beast with a 450-horsepower heart. The engine is a naturally aspirated, 4.2-liter V-8 with 317 pound-feet of torque. A seven-speed S-tronic automatic transmission does the shifting and Audi’s quattro all-wheel drive puts power to the ground.

The RS5 boasts a 4.5-second 0-to-60-mph run with a top speed of 174 mph. Pricing starts at $70,000.

Conclusion

The BMW Alpina D4 Biturbo is a fantastic sports car in either body style, showing that diesel can be just as competitive as gasoline. With a 0-to-62-mph time of just 4.6 seconds for the coupe model -- the convertible requires five seconds -- and a top speed surpassing 170 mph, the D4 is a spectacularly fast machine. What’s more, with a rating of up to 44.6 mpg on the European cycle, the D4 outshines any gasoline competitor for long-haul friendliness.

The bespoke luxuries added here do come at a price, but for those looking for something different than a standard BMW -- even an M-powered BMW -- the Alpina series of cars offers a great solution.