Short Course 4WD is quickly becoming the one of the most popular competition classes in America. To satisfy the power demands that this class requires, Reedy developed the Sonic 550. Designed specifically for the Short Course 4WD class and intended strictly for competition, the Sonic 550 features a lightweight case design with extra-large strategically placed vent holes to reduce operating temperatures. Lower temperatures result in less fade over the course of a race, longer run times, and increased motor life. Read more vie the source link. Source: http://www.teamassociated.com/news/latest_products/653-New!_Reedy_Sonic_550_Brushless_Motors!