None. Engine timing is set by the PCM, you can not change it with a timing light.
do u set the timing marks at btdc or tdc on a 2.5 mercury cougar
The left most notch is 0 BTDC, the middle notch is 10 BTDC, the right most is 14 BTDC for automatic, or 16 BTDC for manual trans.The indicator is a pin sticking out of the timing cover above the crank pulley.Put a jumper wire between T and E1 on the Diagnostic connector and adjust the distributer for 10 BTDC.Remove the jumper and the timing should advance to the rightmost mark, or a little farther.
12degrees btdc
14°btdc
12º BTDC .......+ or - 2º
1 (0 deg BTDC) - 5 (480 deg BTDC) - 3 (240 deg BTDC) - 6 (600 deg BTDC) - 2 (120 deg BTDC) - 4 (360 deg BTDC)
8 degrees BTDC. 8 degrees BTDC. 8 degrees BTDC.
Light duty 14 BTDC, Heavy Duty without catalyst 4 BTDC, Heavy Duty with catalyst 10 BTDC.
This means the timing is set to fire the spark plugs at 10 degrees before top dead center on the compression stroke.
10 degrees BTDC
Inline 6 Auto: 12' BTDC Inline 6 Man: 6' BTDC 289 V8 Auto: 10' BTDC 289 V8 Man: 6' BTDC These are the factory specs. You can usually get away with a little more though.
35 BTDC 35 BTDC