Several custom bikes have recently shown up with 4 cylinder V-Quad engines, essentially 2 Harley Davidson V-Twins joined at the hip. OCC built their Intel chopper, Carl Brouhard built a twin turbo version and there are probably a few others.
Got a note yesterday from Tim, who sent me the link to Nelson Engineering, makers of the particular V-Quad used in these bikes. Greg Nelson is a former HD engineer who decided to bolt a couple of engines together and after machining a few parts, did exactly that. He said the first one fired right up and he has since refined the engine a bit, set up a supply chain and you can order one if you have the desire to put a really big engine in your own custom, bike, go kart, or whatever else you might have in mind.
Specs are 214 cubic inches, 250 horse power, dual 45mm Mikuni carbs, 225 lb. ft. of torque and the prototype, which was a mere 160 inches, gets 40 mpg.
I'm a little unsure how well air cooled V4s work, though Greg says he has one in a bike he rides all the time. It may not be really practical but it looks interesting.
Thanks for the tip, Tim.
Link: Nelson Engineering