I'm not really sure why people are saying that the 1986 Sportster is the best for drag racing. The four-speed '86 to '90 Evo crankcases use the earlier Ironhead-style offset cam geometry, four-speed transmission, and a larger and stronger piston shaft than the 1991 and later five-speed designs.
But, as far as I know, there really aren't significant differences in the 1986 versus all the other four-speed Evo cases that would give the '86s an advantage in performance applications.
I recently purchased a '86 Harley-Davidson Sportster. People have told me that '86 engines are the best for drag racing. What makes them different than the '88 and later ones? Could you give me a small rundown on the differences between them other than the obvious differences you can see by looking at the primary covers? I would like to know if the crank/cam and/or what else is different in the engine. Why have people offered to buy it from me for a drag motor?