1. The engine(s) used to power the car must be four-stroke piston engine(s) with a
displacement not exceeding 610 cc per cycle.
2. If more than one engine is used, the total displacement cannot exceed 610 cc and
the air for all engines must pass through a single air intake restrictor.
3. In order to limit the power capability from the engine, a single circular restrictor
must be placed in the intake system between the throttle and the engine and all
engine airflow must pass through the restrictor.
4. The maximum restrictor diameters are 20.0 mm (0.7874 inch) for gasoline
fueled car