Around 1937, Dale Drake, who was later to become instrumental in developments to the Offenhauser racing engine, began working on a 2 cylinder engine for midget racers. He began with an air cooled opposed twin but eventually took a Harley Davidson Knucklehead engine and installed water cooled cylinders. The result was an 89 cubic inch V-twin that was 10 percent smaller than the Offy midget engines then used but it was lighter at 185 pounds and had more torque and seemed to get better traction on slick dirt than the Offenhauser.
I had never heard of this particular variant of the Harley Davidson engine until I saw this midget racer listed for sale. It was driven by Bill Vukovich Sr. who went on to become very famous in Indy Car racing.
Just last week I pointed to the Model T with a Sportster engine which was no period piece, just a current custom, but this car indicates the Harley V-twin was actually used for automotive uses even back in the 1930s. Pretty neat.
More photos below:
Link: listing no longer available
Reference book for Offenhauser engines contains a brief mention of this engine.