When #1 piston is at its upper most position in the cylinder bore and both intake and exhaust valves are closed
Top Dead Center
Zero, tdc / top dead center
ZERO at TDC./ Top DEAD CENTER
ZERO TOP Dead center.
what engine do you have in your impala?
0 degrees top dead center
0 TDC / Top dead center.
Zero at TOP DEAD CENTER / TDC.
ZERO at Top dead center.
One degree above top dead center.
8-10 deg.before top dead center.
8 degrees BTDC-- Before top dead center.