When you talk about Harley-Davidson performance, do you mean torque, horsepower or both? Torque is twisting power. It's this low-rmp twisting power that gets you moving. Horsepower is the higher-end spinning power that keeps you moving. If you look  for harley davidson gear oil and at the difference between a Harley-Davidson V-Rod and a regular Harley Twin Cam 96, you'll see that the V-Rod with its' 1200cc engine puts out a lot more horsepower than the Twin Cam 1584cc, but puts out less torgue. The V-Rod puts out this horsepower buy spinning faster. The V-Rod is able to spin faster because of its' four valves per cylinder and dual overhead cams. Basically it’s because of the V-Rod's overall breathing ability.