BMW's K4 streamliner - Throwback Thursday

During a tour of the French motor research facility in 1946, Autocar's Paris correspondent, WF Bradley, occurs in two rare BMW that had been seized from the research base Stuttgart at the end of World War 2.

The first is easy to identify - 328 Berlinetta Touring has been driven for the first and only BMW victory in the 1940 Mille Miglia - but the second one a little more curious. Aerodynamicist works stand out Wunibald Kamm, K4 is an experimental car built to investigate the "downsizing, highspeed road-holding and operating economy", in the words of Bradley.

Loss of detail dense, Autocar's men collected what he could of the French engineers. "The body is interesting and surprising, shocking feature becomes almost vertical rear panel," he wrote. "The bottom surface is perfectly flat, the lights set into the wings, windshield rounded off to the side panel and drive wheel is closed."

It was definitely different, based on the 335 spacious luxury models and displays the next 'suicide doors' that depends on the B-pillar, as do conventional rear doors.

K4 has a drag coefficient of 0.196 at the time of the contemporary saloons is about 0.5Cd, but experimenting with aerodynamics without using computational fluid dynamics means that research is a case of trial and error.

In order to make the car stable at speed, there have been experiments with fins. "A single fin, with or without slots, have little effect on the stability and even harmful," writes Bradley. "For no good, fin should have excessive dimensions. Two fins without slots no better. They have a tendency to deviate from the vehicle straight course, and they have a lifting effect on the back.

"The best results are obtained with a pair of fins slotted, actually consists of fin and rudder. The system is implemented in the glass."

K4 has a 3.5-liter six-cylinder, producing 88bhp. The machine is equipped with dual carburetors, "part of which is used for normal walking and other parts that come into action during the final movement of the throttle pedal".

A four-speed gearbox driving the rear wheels coupled with overdrive planet. "The road test by France reveals an extraordinary gain of overdrive," said Bradley.

Although engineers tested on the road consisting of hills, heavy traffic and a built-up area, K4 still returns impressive fuel economy. At 77mph and 1950rpm, it was measured at 24.4mpg; 900rpm at 35mph and it improved to 32mpg. "Certainly much better results can be obtained at autobahnen Germany," contemplate Bradley.

Because of the poor state of this K4 tires, the engineers were unable to test the car at a maximum speed of 90mph. The car also has an automatic tire pressure regulation to modulate rolling resistance, although some parts of the system are missing and engineers were unable to verify the effectiveness.

K4 fate is unclear, but most likely it was dismantled by the French engineer curious to learn all the secrets. The philosophy behind the car is still important to BMW as usual, with the 2009 Vision Efficient Dynamics concept hailed as the modern equivalent of the K4 and in turn inspire i8.

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