Timing for electronic ignition upgrade
At least through the early 70s, the initial portion of the advance was very fast, and very long, then the secondary curve was similar to pre-smog.
An extreme example of the difference is the 273 Federal versus California Manual trans with Clean Air Package in 1967.
Idle rpm spec also increased because they couldn't run well at the lower rpms with retarded timing and leaner idle mixtures.
Long FAST curve.
At least through the early 70s, the initial portion of the advance was very fast, and very long, then the secondary curve was similar to pre-smog.
An extreme example of the difference is the 273 Federal versus California Manual trans with Clean Air Package in 1967.
Idle rpm spec also increased because they couldn't run well at the lower rpms with retarded timing and leaner idle mixtures.