The 426 Hemi also was used in NHRA and AHRA drag racing. Its large casting allowed the engine to be overbored and stroked to displacements unattainable in the other engines of the day. Top-fuel racing organizers limited the bore spacing of engines until very recently, when under pressure from Ford and other manufacturers, the bore spacing allowed was increased to —this allows other engines such as the Ford 385 series to begin to compete. The engines based on the old Chrysler design predominate Top Fuel and Funny Car classes due to plentiful parts, a large amount of research and development, as well as decades of experience with the problems of the engine's design. In drag racing today, the engine bears little resemblance to any engine produced by Chrysler; it is usually equipped with a large Roots type supercharger and short individual exhaust pipes, and fueled with nitromethane. Yet, this variant is used in Top Fuel, Funny Car, and Pro Modified classes.