1963 NASCAR International Rule Book Specifications NASCAR Grand National Championship Circuit Section 20-7 -- Exhaust

a. Muffler must be removed. Standard exhaust manifold and header-pipe for make and model only. No alterations or changes permitted from the engine block to muffler take-off. Pipes from muffler take-off must be no larger than four inches inside diameter when round exhaust pipe is used. Any other system must be approved by NASCAR. Exhaust pipes must extend past driver and to the outer edge or rear of car, with a minimum ground clearance of four inches.

b. Extra brackets permitted.

c. NASCAR reserves right to reject improperly mounted or unsafe exhaust pipes.