The origin of VW tuning – Type 174A, 1942-1943

The Type 174A engine. From this angle it looks like a pretty normal kdf engine with dual carbs.

The last in the row of Sturmboot prototypes is the 174A. In the specifications I have seen it is said to be a normal kdf-engine, but with higher compression, larger intake valves and dual carburetors. But, was there perhaps something else done?

I want you to put yourself in the shoes of the Chief Engineer for the Sturmboot engine program. Your first attempt, 170, was a rather simple execution: Slap a Roots supercharger on to an existing engine. Simple, but in the end too heavy for the application.

Your next try, 171: An engine that is totally re-designed only to be able to get hemispherical combustion chambers. A nice solution from a design point of view, but tooling up for a entirely new engine, aimed for a very narrow application, would have been insane.

So, what to do next? Obviously there is a resistance in increasing the cylinder volume* and there is also a belief that hemispherical combustion chambers is the way to increase power in a normally aspirated engine (perhaps it was also deemed as a necessary measure to be able to raise the compression with the war-time fuel). On top of that, the new engine must reuse as many kdf parts as possible.

If only there was a way of tilting the valves while still retaining the overall lay-out of the kdf engine. Hmmm…. Wait a minute! If I tilt the valves in the other direction? Never mind the intake valves, perhaps only tilting the exhaust ones would be sufficient to get a much better combustion chamber? If we can find a way to get the pushrods on the exhaust side to work despite the angled valves, we can have a nice high compression engine, reusing most of the kdf parts. Then we only need tooling for new heads and we don't even need to touch the casting of the case! While we're at it we can add dual ports on the intake side for better flow, much like the early E60 engines from the 1930's.

This, ladies and gentlemen, describe the design principles of the type 369 head, a design that would follow Porsches pushrod engines in all 356 and 912 up until the late 60's.

Viewed from this side we see that this is not normal kdf-heads. They have dual ports and very different valve covers (I did the yellow high-lightning for illustrative purposes).

Look at the picture above of the type 174A. I have highlighted the shape of the valve cover and the dual port intake. Then compare it with the very early type 369 engine found at the Prototyp museum in Hamburg. I think the similarities are striking.

An early type 369 engine from the Prototyp museum. Compare this to the previous picture. To me it seems as the type 174A was the true father of the Porsche 356 heads.

Could it be that the 369 engine launched by Porsche in the late 40's was a carry over from the war time type 174A? Phil Carney (356 Registry vol 32, nr 6) writes that it's "quite possible" that the type 369 heads "were initially designed during the war". Not exactly heavy evidence, but I can't find any information that goes against my theory that the type 174A and 369 heads are closely related.

Again, any additional information that can support, or destroy, my theory is very welcome. To me the sketch of the type 174A is a good indicator that the Porsche 356 pushrod engine had its origin in the Sturmboot motor type 174A from 1942/1943.

*The cylinder volume was already increased a bit from 998cc to 1131cc, but I see no attempt in going further.