T he Volkswagen factory never admitted that it would be wise for safety, or at least necessary to increase the engine power of the flat four. The agents had even been warned that any mechanical alteration would cancel purely and simply the manufacturer's warranty. But as this is often the case, some did not resist to their wish to boost the small VW engine, starting with one of the most famous preparators, Ferdinand Porsche, its inventor. While on one side, companies such as Okrasa in Germany and Denzel in Austria chose the "atmospheric" option by conceiving crankshafts with longer stroke and special heads with double carburettor, others, like Judson in the U.S.A. or Amag in Switzerland preferred to compress the mixing of air and gas.

To understand why the principle of the blower (or boost ?) is so popular on a VW engine, let's see how it works.

	On the left, the mixing arriving from the carburettor gets inside the space between the 2 blades that are outside at the maximum in order to make the system proof. On the right, the space is reduced because of the decentered axle, the vanes get into their lodging and when arriving opposite the admission pipe inlet, the gaz expand.

Here the Beetle "Ovale" belonging to Ulf Kaijser, with its original equipment. Note the double notch pulley that leads the blower.