You've intermixed two terms that, at least here in the U.S.) would be contradictory.
Motorbikes are small, innocous little scooters that are incapable of making much noise due to their size.
Motorcycles, on the other hand, can range from 50 to maybe 150 horsepower or so (as seen here:
http://www.visordown.com/motorcycle-top-10s/the-10-best-motorcycle-engines--ever/9854-5.html ).
But notice, in the link, that the higher horsepower engines only achieve that H.P. at relatively high revolutions per minute (RPM's). That is the major difference, since an automobile engine achieves it's H.P. at much less max RPM's.
But, of course, most riders that wear the head scarves, leather jackets and beards (male or female) want the notoriety of high handle bars and magnificient noise... hence the drilled out, baffling removal and accentuator tailpipes often seen on "Hog" riders. It's a way of saying "Look at me!", not unlike the driver of the sedate but noticeable 1964 Chevrolet Corvette Singray he has just spent $40,000 purchasing and rehabilitating...