1965 NASCAR International Rule Book Specifications NASCAR Grand National Championship Circuit Section 20-7 -- Exhaust

a. Muffler must be removed, exhaust manifold optional. 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 the car, beneath frame, with a minimum ground clearance of four inches.

b. Extra brackets permitted.

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