Great information! When were dual exhaust resonators added in 1969? Thank you in advance…
There are two separate discussions on this topic: Z/28 and Camaro SS with L34 or L78 engine.
All Z/28s built from the start of production through December 3, 1968, had chambered exhaust as standard equipment. It was too loud for some areas; owners were being ticketed. A recall was issued, replacing the chambered system with a single transverse muffler system w/o resonators. Chambered became optional where permitted. The recall system was still too loud under certain conditions, so a second recall was issued. In production as of May 3, 1969, Z/28s were built with a single muffler/dual resonator system. As of May 19, chambered was dropped as an option and chromed tailpipes were added as standard equipment.
Camaro SS with L34 and L78 engines built from the start of production through December 3, 1968, had chambered exhaust as standard equipment. They were also included in the recall; according to the recall parts listing the system could be replaced with a non-resonator system similar to Z/28. What they did in production is in question. There are few surviving cars with original exhaust. Vintage undercarriage photos of ZL-1 #3 [built March 4] shows a production welded muffler/resonator system. The excellent original black L78 car [built February 26] displayed at the MCACN show last year still had much of its original welded resonator system. However, the equally nice silver L78 car at the show in '21 still has its 100% original welded non-resonator system. The only real difference is the resonator cars had 4.10 axles, the silver car has a 3.73 axle.
What dictated which system? My theory is SHP big-blocks built with 4.10 gears received resonators. I am aware of the red COPO at the show that allegedly was built without them. It had a rough life and a history of owners, no absolute certainty the system on it was original.
In case you were wondering, The AIM, recall notices and P & A manual conflict with the few survivor cars with original exhaust. P & A manuals list both systems without specifying application. The N10 section in the AIM lists a change as of June 13, 1969. Taken literally, it indicates all L34, L35 and L78 would be built with the welded resonator/muffler system. However, there are two late production L35 survivors with original, non-resonator systems. My guess is the standard L35 system was muffler/no resonators.
We could use some help. Big blocks with original exhaust top the list. The Chassis Broadcast Copy lists the production exhaust system in box 198. Known BB codes are FR, FS, FT. L48 and Z/28 codes are FM January-late April, then FQ.
