Typically timing specifications are listed in "degrees before top dead center", however, on some very high compression engines those specifications may be different.
Check a shop manual for the specifications for YOUR engine.
your timing is out bring the engine to top dead centre at the first plug from the front of the car, some cars you most set the timing before top dead centre .
4 degrees before top dead center / BTDC
8 degrees before top dead center.
The timing should be set at 12 degrees before top dead center. If this is a Canadian heavy duty engine, it should be set at 2 degrees after top dead center.
TDC, top dead center is when the number 1 piston is at the top of the cylinder. 8 degrees before TDC is where you set the distributor so that is when the spark plug fires. You use a timing light to set the distributor. There is a timing mark on the crankshaft pulley and a series of marks on the timing chain cover that will show where 8 degrees before is at. The timing mark on the pulley is a small notch in the edge of the pulley closest to the timing cover.
8 to 10 degrees BTDC / before top dead center.
8 degrees before top dead center.
6 to 8 degrees before top dead center. STOCK ENGINE
6 degrees before top dead center on the 305 TPI
with a timing light, assuming this is an older engine that still uses a distributor.
The timing for the 1977 225 slant 6 cylinder should be set at 2 degrees before top dead center. This applies to both the manual and automatic transmissions.
It is look like ruler with 0, 10, 20 number XXXXXXXXXXXXXXXXXXXXXXXXXXXXX The timing scale will have an "A" at the top and a "B" on the bottom. In the center is a "0". The "A" is for after top dead center. The "B" is for before top dead center. Each mark on the scale is 2 degrees. Timing is always set on before top dead center.