The origin of the V-head: Part of the Berlin-Rome race car program, or a dead-end development for a sturmboot? (Photo by the author taken at the Prototyp museum in Hamburg)
Back in the 1940's VW hot rodders did not have that many choices to get a better breathing intake system. The Okrasa and Denzel heads would not be available until the 1950's and the Porsche head was not introduced until 1949.
But, a handful of prototype heads with better breathing capability did exist. I am talking about the famous so-called V-heads which had hemispherical combustions chambers with large valves placed in a V-position. They were used successfully by many racers in the late 40's: Petermax Müller, Kurt Kuhnke and Otto Mathé to name the most famous ones.
The Porsche Type 367 prototype from c:a 1948
using left-over V-heads. *This was one of three concepts for the Porsche engine, this one was deemed to be too expensive to manufacture. The type 367 prototype engine was sold to racer Otto Mathé together with the last remaining Type 64 Berlin-Rome car.
The British magazine Classic and Sports Cars (December 2007), takes a closer look at the restoration of one of the two existing engines (from Petermax Mullers race car). They mention that the gas welded valve covers and the machined pistons points at the fact that the parts were prototypes ones, rather than actual production parts. In my mind it strengthen the theory that the heads were not (production) Sturmboot heads.*
Looking at the list of Porsche design project number in Ludwigsens book I see two possible scenarios. One is that the heads were developed as part of the Berlin-Rome race car project in 1938-39. A couple of project numbers (64 and 115) could have had the heads as part deliveries. Carney promotes that theory pointing also at statements in the book Birth of the Beetle by Chris Barber regarding various experiment with a high performance KDF engine for the Berlin-Rome race car.
The other scenario is that the V-heads were designed for the Sturmboot, but never used. There are two project numbers for Sturmboot engine development (170 and 171, during 1942) followed by a final, number 174, with the title Sturmboot engine using normal kdf-engine. One could guess that the first two were more adventurous dead ends followed by a final simpler and more straight forward solution. The V-heads could theoretically come from the first two projects.
But, looking at designer logic I think the Berlin-Rome alternative makes the most sense. In a race car engine the rules of the race class sets the limitations, thus all parts need to be optimized with this in mind. In military applications the design criteria are different and there are no rules banning increased cylinder volume or super charging. I see it more logical that these advanced hemispherical heads stem from race car development rather than military applications. Until new facts surfaces I hold it as the most plausible theory.
*Edit November 2015: Since this post was written new material has surfaced. The type 367 heads are not same as the Sturmboot type 171 ones. Follow this blog for more information, I will tag all new posts on this subject with "V-heads"