1973 NASCAR International Stock Car Racing Rule Book NASCAR Grand National ® Championship Division Section 20-6 -- Cooling System

a. Water pump impellers may be altered.

b. Removal of fan blades, fan belt or air cleaner not permitted. Any NASCAR approved air cleaners allowed, and they must have the complete element. Only standard minimum four blade fan permitted. This applies to all late model divisions as well as speed trial and record attempts. The pitch of fan blades may be changed, however fan blades must maintain standard size width and length for make and model. Only steel fans permitted.

c. Interchangeable radiator cores are allowed providing they do not alter sheet metal or frame of radiator for make and model. Radiator must remain stock appearing and remain in standard position.

d. Radiator dust screens permitted.

e. Any brand or make of radiator hose or hose clamp permitted.

f. Radiator overflow pipe may be relocated or extended to not more than six feet.