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. Engine blocks and cylinder heads are often provided in a "raw" condition with only approximate dimensions and rough machining. Each team will continue to machine and modify the part to their own standards. NHRA pro stock engines are restricted to a maximum single-camshaft, 90-degree V8. Several bodies have different rules. "Mountain Motors", run by the PDRA (eighth-mile) and at selected NHRA events in 2019, do not have a 500-cubic inch rule, with some engines exceeding , to upwards of . The NHRA limits engine displacement in Mountain Motor categories to . The Australian National Drag Racing Association and IHRA have a maximum displacement engine limit. Depending on sanctioning body and class, engines may either be four-barrel carburetors or throttle body electronic fuel injection and must be a naturally aspirated intake system. Those that use two four-barrel carburetors may allow them to be "split" (i.e. sawn in half) so that each of the halves can be more accurately positioned over the slightly staggered intake runners. The intake manifold and heads are open to modification. The most effective intake manifold configuration has continued to be the "tunnel ram" for nearly 40 years. The carburetors are raised above the engine; the length and configuration of the intake passages ("runners") is critical to horsepower output. The tall intake manifolds necessitate the large hood scoop that is a signature of the pro stock class. (The hood scoop is illegal in the NHRA because of EFI) The NHRA formula (starting in 2016) requires, and the PDRA extreme pro stock permits, cars to use electronically controlled throttle body fuel injection systems. In the NHRA, an electronic control unit (ECU) will be implemented on the EFI systems, including a 10,500 RPM limit, with modern engines approaching 12,000 RPM.
The rules that exclude forced induction of any sort, plus allowing head modifications, have resulted in pro stock heads being the most sophisticated in any drag racing category, with valve lifts in the 1 inch region.
Modern pro stock engines generally produce around 2.5 hp/in3 (114 kW/L), and make upwards of 1,500 hp while being naturally aspirated.
A complete NHRA pro stock engine can cost upwards of $100,000.