A prototype of the type 171 Sturmboot engine dated 1943
Next in line for the air-cooled Sturmboot project was project 171. This time a normally aspirated 1131cc pushrod engine with hemisphearical combustion chambers. The inspiration of the heads seems to origin from the pre-war SOHC type 115, but this time a bit more conventional using pushrods from a centrally placed camshaft.
To me it's a mystery why they did chose to go to this rather complicated design instead of increasing the cylinder volume, a solution that would have required less amount of new parts. Somehow I have the feeling Porsche took this military order as an opportunity to make designs that could be useful in future projects after the war. According to my source document this rather novel design was scrapped due to the cost (and probably time) it would take to put it into production. Not many details remained unchanged from the original kdf-design.
As can be seen not many parts are interchangeable with the original kdf-engine. A fact that was to be the fall of this concept.
But how far did the development of this engine go before it got stopped? Both the document I have access to and Chris Barbers book "Birth of the Beetle" indicates that of the different air-cooled Sturmboot designs only type 174 was ever tested in a the real application. However, from the picture above we can assume that a prototype of the 171 was made. According to one of the worlds leading kdf-experts only one prototype of each (170, 171, 174) were made and they were all later scrapped in Linz/Donau in 1960.
Some believe that 171 heads were used by Kurt Khunke in his VLK (Vollstromlinien-Leichtbau-Konstruktion) in which he won the 1947 Braunschweig Autobahnrennen (first ever victory for a kdf/VW based vehicle). This has not been confirmed and if only one prototype of a complete 171 was ever made this seems highly unlikely. From the design it is obvious that these heads can not be used on a kdf engine as the case is very different. My conclusion is that we can probably rule out that the 171heads were ever used in racing applications (I welcome any fact that can strengthen my theory, or destroy it).
In some current litterature the V-heads in Peter Max Mullers race car, displayed at the Prototyp museum in Hamburg, are referred to as Sturmboot heads. Looking at this picture, showing one single valve cover for two cylinders, I think we can safely rule out that connection.
If anyone has more information, please contact me! If new information surfaces I will share it on this very blog.