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Discussion Starter #1
So during the mid to late 30's, a company called DKW was the world's leader in 2 stroke tech. For their race bikes, they used a "Split single" that was supercharged through a variety of ways. The supercharging effect was utilized by the engines asymmetric port timings ( Exhaust opens, transfer opens, exhaust closes, transfer closes) as opposed to symmetric port timing (exhaust opens, transfer opens, transfer closes, exhaust closes). Sadly, due to new racing regulations and ties to Nazi Germany, the company left racing to produce motorcycles for the war.

I was researching their pre war bikes when I stumbled across this design.

21026d1391775545-szivomembran-jawa-350-638-dkw.jpg
So while looking at this I noticed 2 plugs, one is obviously a spark plug, but I was wondering what the second one was. A fuel injector? A water injector?
 

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Don't know, looks like an injector, don't it. But I can give you a little info. The split-single engines were like a 2-stage air compressor in that pressurized air or air/fuel from the first cylinder went to the second cylinder where it was further compressed before ignition. In other words, it was a supercharged 2-stroke. Probably the extra cost and complexity, and extra rotating/reiprocating weight which would tend to limit rpm, caused this design to be dropped, especially with the advent of the expansion chamber exhaust, which has a supercharging effect without any moving parts. But into the early Sixties, until the Japanese bike invasion, you could buy a 125 or 250cc Allstate bike from your local Sears, Roebuck. The split-single or twin-single engines and bikes were built by Puch in Austria, pronounced "Pook," but of course we referred to them as "Puke twingles." But I never saw one up close, and can't answer the question.
 

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I think Walter Kaaden (spelling on last name unsure?) Kaden, Kaadan, perhaps was one of the principle engineers at DKW and was sort of the father of 2 stroke design from what I've read and understood. You might learn a bit more by researching out him.

I'd concur that the amount of additional moving parts and weight was probably the reason the design didn't ever really take off - but who knows for sure.
 

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Certainly good for their day; DKW won a bunch of races in the late-Thirties with a 250cc four-cylinder twin. Wonder how they measured displacement on those things . . . it would be a little like the controversy of how to measure displacement of a Wankel rotary.
 

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Discussion Starter #5
They measure the displacement essentially the same way as if it was a 2 cylinder. Split singles are considered singles because its just an opposed piston engine bent 180 degrees. By the way, it wasn't 250cc, it was 350cc
 

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Discussion Starter #6
The reason the design lost popularity was because a poor under piston compression ratio, and cost. Because the main reason 2 strokes are used is because they are light weight and cheap, the split single became obsolete.
 

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Discussion Starter #7
You're wrong about one cylinder being a compressor and another being a combustion. the real way they work is that the mixture travels up the bore with the transfer ports, through the cylinder head, and down the bore with the exhaust ports.
 

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You're wrong . . . .
Yeah!! And you've done me a favor in saying so, Mansfield. My erroneous description is something that I have "known" for about fifty years, since someone favored me with that explanation. Now I'm googling "split single" to get a handle on how the thing actually does work. Sorry about giving out bum information, but glad you knew better and have put me on the right track.

What's the saying, something like,"It ain't what you know, but what you know that ain't so . . . "
 
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