[William]

Chambered exhaust became a problem for Chevrolet.

Initially standard equipment on Z/28s, 350 & 375 hp 396s people were getting excessive noise tickets prompting Chevrolet to discontinue the system as standard equipment as of November 25, 1968. Undoubtedly caught short of some exhaust system components for Camaro there was an interim system of a transverse muffler without resonators, same as the 67-68 "deep-tone" dual exhaust. Later systems included resonators as depicted in the Aug '69 Hi-Perf Cars road test of ZL1 #3 - assembly line systems had the resonators welded to the exhaust pipes. People that had been ticketed could have the standard dual exhaust system retro-fitted at no cost and this is what the letter explains, listing the parts to be used.

As shown in the assembly manual [NC8] the RH rear chambered muffler was welded to its tailpipe. The LH rear muffler used a conventional tail pipe secured with a U clamp. Each muffler had 2 tabs and were bolted together. The ebay system is a collection of mismatched parts: 2 LH rear chambered mufflers and standard muffler 2nd design tailpipes.

Chambered is not a hi-performance exhaust system. True ZL1 guru Bill Porterfield built a ‘resto’ ZL1 engine and dyno-tested it for the February 1995 Chevy Hi-Performance magazine. Simply removing the chambered exhaust system added 80 hp. Todays Flowmaster systems cost 0 power.