1969 Camaro Smog System Question

[Unreal]

Chuck, You may be right, but my BB with A/C smog is also over the valve cover. I have hydraulic valves, so I seldom need to get into my valve covers. But when I do, I have to remove the smog hose and check valve.
You would need to do that every time you adjust the solid lifter valves. I wonder why GM would switch to the over cover one, when the front one would eliminate the need to disassemble the smog hose.

[Mr70]

The BB front one,-Left one..aka "Hockey stick" design,Part 3940933,will not work on vehicles with Air Conditioning,as the compressor/bracket gets in the way.
They used they the later issued #3981061 "Over the center of Valve cover" design for that,and continued with it well into the 1970's.
The 1970 Chevelle Assembly manual calls out the Left side revision on 9/12/69,but I can tell you that it didn't happen on all Chevelle/Elco's that fast and at all 6 solid lifter plants at the same time.Chevrolet used up the earlier issued "Hockey stick" design up to around January of 1970.
This is my own opinion based on talking to original owners,seeing their vehicles,Chevrolet archival photos and Car magazines road test articles on these vehicles from back then.

[Unreal]

Rick,
I know that's why they used the over valve cover one on A/C cars. My point was that if they used the A/C type one on a solid lifter car, they would need to remove the check valve every time they adjusted the valves. It doesn't make sense that GM would use the over cover unit when they had an alternative already in the parts bin that would not require disassembly to adjust the valves.

[Mr70]

It was probably all about cost & simplicity to themselves.
Why make two design tubes,when one design would accommodate both,where as the earlier would not.As at that time,they were well in the planning/design stages of the 71-72 models,most likely seeing the writing on the wall with the mandatory implement of A.I.R being required on ALL vehicles in the upcoming years,which meant A/C equipped Hydra lifter BB too.
Add to that,I think they pretty much new 99.9% of all new car Hi-perf owners were going to pitch the entire A.I.R. system within one hour of taking delivery anyway,so it getting in the way of adjusting valves would become a moot point.

[nuch_ss396]

[ QUOTE ]
....Add to that,I think they pretty much new 99.9% of all new car Hi-perf owners were going to pitch the entire A.I.R. system within one hour of taking delivery anyway,so it getting in the way of adjusting valves would become a moot point.

[/ QUOTE ]

Rick,

That is exactly what I believe the rationale was for use
of only the over the valve cover tube design. Does anyone
remember seeing a SHP engine with the AIR system intact
back in the day? I sure don't.....

Taking off the SMOG system didn't cost anything. You
gained some HP! Weren't we all trying to squeak as much HP
out of these cars as we could?

And as you've observed, GM knew most SHP owners were removing
these systems to gain HP. So it was a

Steve