Pro stock is a class of drag racing featuring "factory hot rods". The class is often described as "all motor", due to the cars not using any form of forced induction such as turbocharging or supercharging, or other enhancements, like nitrous oxide, along with regulations governing the modifications allowed to the engines and the types of bodies used. History The National Hot Rod Association pro stock class emerged from the production-based super stock in 1970 with a more liberal set of rules and an absence of handicaps. Rules initially favored big block V8s with Chrysler Hemi engine powered cars winning the world title the first two years. The NHRA attempted to balance the playing field for 1972 and introduced rules allowing for small displacement V8, compact cars carrying favorable weight. On 1 July 1973, the NHRA required pro stock drivers to have competition licences, just like blown or fuel dragsters and funny cars. Following a 1973 NHRA rule change to allow records to be set at any national meet, at the 1973 NHRA Winternationals, "Dyno Don" Nicholson set the first official pro stock e.t. record with a 9.33, while Bill Jenkins turned in a record speed; later at the same event, Nicholson made a 9.01 second/ pass, breaking both his and Jenkins' records. Over the 1974 and 1975 seasons, Bob Glidden became the first driver to win two pro stock championships. In 1982, the NHRA did away with the weight break system and implemented a 2,350 pound minimum weight, 500 cubic inch maximum rule across the board, due to the popularity of the Mountain Motor IHRA pro stock cars, which have unlimited displacements. Lee Shepherd won the second of four championships in a row in 1983, the year he also won IHRA's title, making him the first driver ever to do so; he repeated the feat in 1984. In 2016, the NHRA implemented a major overhaul to the engine formula. Hood scoops and double four-barrel carburetors were eliminated and replaced by electronic fuel injection, an overhaul designed to reflect modern automotive trends, as all automobiles being produced for sale in North America have used electronic fuel injection for over 20 years. Pro stock today Engine Except in the NHRA 500 ci formula (starting in 2018), the engine must be manufactured by the same company as the car body. All raw components must be available to anyone for general public purchase.