Engine Timing, The Synchronized Dance Inside Your Engine.
All engines start off with a base timing figure called initial timing. This is established with the physical position of the distributor in relationship to the engine.
Ignition-timing figures are always delivered in crankshaft degrees and in relationship to the No. 1 piston at top dead center (TDC). This means that any ignition advance will be expressed in terms of degrees before TDC (BTDC).
This is important because some enthusiasts get confused when viewing timing markers on engines where the timing tab may be embossed with ATDC and BTDC. The confusion here is that some people mistakenly think that the “A” in ATDC means “advanced” when it really means “after,” as in “after top dead center.”