How are motorcycle engines able to make so much power with such a small engine compared to car engines?

Revs. Horsepower is a product of rpms and torque, while car engines rarely reach high revs they do produce high torque (mainly due to their size), bike engines on the other hand produce (for their size) reasonable chunks of torque (modest for a car) they also make higher revs (or are engineered to make higher revs), so they get higher horsepower. This is at the expense of servicing schedules and component life.