Speed isn't everything.
Joel Zumaya was an 11th-round pick out of high school in 2002, a projectable kid with an average fastball. In his first spring training in 2003, he showed up with (depending on whom you ask) an extra 8-10 mph on his fastball. In less than four years after he signed that first pro contract, he was an impact pitcher on a pennant-winning club.
Juan Morillo signed as a free agent in the Dominican Republic in April of 2001, and is probably the only man in baseball who can consistently match Zumaya for raw heat. He got his first cup of coffee in September of 2006 and was pounded; before his recall, he posted a 4.62 ERA in AA.