Curt Winter's big twin racer sparked a discussion about big twin racing in general, it seems quite a few folks think it would be a Harley Davidson series and of no interest to anyone else. Doug dropped a link in a comment to this sweet looking machine from Japan's Over Racing, it's the OV-23XV, built around the 1670cc air cooled V-Twin from the Yamaha Warrior and MT-01. To me, it looks like a pretty serious piece.
The bike was built back in 2004 for the Suzuka 8 hour endurance race and it didn't qualify or the next year, either, though, according to an article by Alan Cathcart, it was very close.
The bike Cathcart rode weighed 460 pounds with 115 horsepower and 115 foot pounds of torque. Each cylinder was topped with 4 valve heads and twin injectors.
It would be interesting to see if the engineering in the intervening years since this bike was built could improve on the previous efforts, but it shows these engines have the ability to make for some very exciting racing. Looks like it wouldn't be just Harley Davidson after all.
Link: Over Racing