An Improved Production race car is a modified road car intended for race track use, and is made popular by the fact that it is fast and can be relatively inexpensive. Based on a production body shell, with limited modifications to engines, brakes and suspension - a popular formula with beginners and experienced competitors alike. You are allowed to install a larger or different engine from the same manufacturer as the body shell, with freedoms permitted with head design, internal specification and capacity. The same style of engine (cylinder count, etc) must remain. Popular conversions include late model twin cam 4 cylinder engines into early model 4 cylinder cars, and 13B rotaries into early model Mazdas. Turbos can also often fitted to various cars.