Basic data for the type 170 engine dated 1943. As can be seen the original compression ratio of 5.8 was retained despite the use of a supercharger (Gebl.).
In 1942 three new project numbers aimed for the same purpose saw the light of day at the Porsche Designbureau: 170, 171 and 174. The background was a problem with the Sturmboots (a kind of simple motor boat with a very long propeller shaft) in which dirty water did clog the cooling system. The idea was to replace it with an air-cooled engine, but the only one in production, the kdf, was not powerful enough. Thus, Porsche Designbureau was consulted to fix the power issue.
In this blogpost I will focus on the first one, type 170. It was a pretty normal 1131cc kdf engine, but with a Roots type supercharger mounted axially behind the crankshaft. Remember my reference in the last blogpost to Barbers book "Birth of the Beetle"? What he claims to be a type 115 engine looks very much like a type 170 mounted in a car. Also looking at the timeline it makes sense. According to Barber, the first version of a kdf engine with axial Roots compressor was completed in September 1942 which is more in line with project number 170 than 115 that is dated to 1939.
This is the only picture I have found on the type 170, I have chosen to zoom in on the axial mounted Roots type super charger (the rest of the picture was of poor quality anyway)
From a business point of view my belief is that the type 170 should have been killed already before the drawing stage. The engine was far to heavy for its purpose due to all the parts surrounding the supercharger. But, perhaps Porsche did proceed with the project just so he could put the high power engine in Ferry Porsches private kdf-cabrio? Who knows…