Gentlemen;
Back to basics:
The HEI distributor has two moving parts. The shaft, which is driven by the camshaft and the housing, which is rotated (in phase)by the person installing it.
It's acessorie(s), the advance mechanicims cause the spark to fire sooner/ahead (out of phase) because fuel burns at the same rate no matter what speed the engine turns. Hence the term BTDC.
"Thats All Folks", end of story!
Yours truly, JM..
