Timing Dist SH

Gordo

For maximum horse power you want the fuel burn to end at about 10 degrees ATDC. Higher compression and richer mixtures burn faster than low compression and leaner mixtures. At maximum throttle you get the most fuel charge into the cylinders so you will have maximum compression. As the governor closes the throttle from the full open position the compression will drop off and the time it takes the fuel to burn will be increased. Without a vacuum advance or some other means to advance the timing, you need to set the timing for maximum power at maximum advance at rated speed under full load. Then retard the timing until the power just starts to drop off. Under any other conditions the timing will not be optimal, but if it is advanced more you risk burning pistons and scoring sleeves. Newer engines with lighter pistons are more likey to suffer from this as their pistons are lighter and can't get rid of the heat as fast as the pistons in the old letter series.

Higher octane fuels can use more advance because they take longer to burn. However since you still want the fuel burn to end at 10 drgrees ATDC, advancing the timing will not necessarily give more horsepower because now more of the fuel burn is occuring BTDC.

Gordon