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.

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

This is the only type 174 picture I have seen. Not a 100% normal kdf-engine as you can see.

As said before the type 174/174A is somewhat of a mystery. In this post I'll try to cover the first one, the type 174.

Looking at the technical data it looks like your normal post-war 1131 cc with 25 hp and a 5,8:1 compression ratio. But the only picture  of a 174 I have found show some strange things.

First there is a bulky device where the distributor should be, which seems to be some kind of magneto device. "Normal" kdf-stationary engines did have a bulky magneto device somewhat similar to this one on the type 174, while the type 171 had a Scintilla device of the type used on post-war stationaries. I guess they tried out different types during the war before they settled for the Scintilla type.

Technical data of the type 174/174A.

The second thing is the carburetor that looks a bit different from other ones from that time. It it's a Solex 26vfi II with dual float bowls that was also tested on the Schwimwagens*. Perhaps it was an attempt to try out a carburetor more suitable for use in a boat application? 

And that's all for the type 174. I have no more at this point in time. Next up is the 174A.

*Edit note: I did update this blogpost with additional information from Dieter and Lucian. Thank you!

The origin of VW tuning – Type 170, part 2

The first version of the type 170 featured a top mounted Roots supercharger, the photo was taken in March 1943.

This blogpost was supposed to be about Sturmboot prototypes type 174/174A, but when asking my source some follow up questions I received some more very interesting information. So until this new information is digested I will wait with the174/174A post, but until then I have some new findings related to type 170 I want to share.

As it turns out, type 170 were built in two versions: One with the Roots supercharger on top of the engine and one were it's axial mounted in line with the crankshaft. The first one is labelled version one and the photo is dated March 1943. The latter does only say type 170 and 1943, with no further details.

The new photo material of Sturmboot prototypes I got show different versions of prototypes and even complete units that appear ready for the sea. This put my statement in earlier blogposts in a new light. Probably no one knows for sure anymore how many prototypes were made.

The second version had an axial mounted Roots supercharger. Could this have been the engine that ended up in Ferry's kdf cabrio? To me it seems like the earlier version above would have been more practical...