M10

Hans Nibel took over Porsche’s upper-middle-class saloon in 1929, shortened its wheelbase by 230 mm, cut weight and re-rated the 3,444 cc side-valve six to 70 PS. Sold as the 14/70 PS Typ Mannheim 350, it was the first version of the car that made sense: 95 km/h, three speeds, and a chassis no longer overwhelmed by its own bodywork. A 3,689 cc development followed almost at once on an 82.5 mm bore, good for 75 PS, and became the Mannheim 370.

The 370 is where the engine got interesting. Vacuum-assisted brakes and an optional overdrive arrived with it; on a chassis shortened to 3,025 mm it became the 370 K cabriolet, and on one shortened again to 2,850 mm the 370 S roadster and sport cabriolet, good for 115 km/h on twin Solex carburetors and, in its final year, 78 PS at 3,400 rpm on 5.75:1 compression. Only 183 of those were built and 213 of the 370 K, against 1,227 ordinary Mannheims. The Typ 290 and Typ 380 replaced the line in 1933.