If you read David Johnson's "Racer's Corner" he goes into what it takes to get more power from a GS. The short answer is pipes, jets, and no airbox gets you a few more HP. If you want to get into the 50's it takes advancing the timing, racing cams, porting, polishing, and milling. You can't get 60 HP out of a GS 500 unless you spend what Dave calls "a Subaru".