Prior to about 1962, Chevrolet trucks were equipped with round straight through mufflers. These units reduced back pressure and allowed the engine to breathe to its full potential. This caused a little extra exhaust noise in comparison to the larger more engineered oval car mufflers but trucks were for work and power.
About 1950 truck mufflers were given slightly larger inlet and outlet pipes. This allowed increased air flow which related to the slightly larger carburetor installed that year.
During the late 1960’s the Chevrolet truck Master Parts Catalog no longer listed mufflers. It appears they discontinued these units and left them to be provided by auto parts stores. By about 1995 the larger 1950’s straight through muffler was the one style available and any remaining older pipes were modified to fit 2″ inlet and 1 7/8″ outlets. Length is about 20 ½ inches.
The cars were lower to the ground and thus, required an oval muffler. This oval shape allowed it to be higher and less likely to hit an object on the road. Trucks were high and a round muffler was satisfactory.
Correct copies of these mufflers are available from Jim Carter’s Classic Truck Parts and a few other full stocking GM truck dealers.