Posted by Janicholson on January 09, 2010 at 10:23:34 from (64.61.211.105):
The point at which peak mean effective pressure is achieved in the cylinder depends on four (primary) factors, the speed of the engine, the octane rating of the fuel, the temperature (at the top of the compression stroke in the cylinder), and the compression pressure. These affect the flame propagation rate, and thus the point at which spark based ignition should occur. The near zero RPM of hand cranking, and the resulting modest compression, and ambient temp. usually need a TDC setting for zero chance of kickback. This should be the setting for all ignition systems used on hand cranked engines. It does not drive the total advance, nor does it affect the advance curve. If modern fuel is considered, and RPM is still at 1600 to 2100, total advance must still be in the mid to high 20s. This is due to the relationship between flame propagation rates and RPM. In slow turning, low compression engines, compared to the Automotive engines of today, the advance seems insufficient, but if taken higher it will detonate. Advance should be set to produce the first hint of detonation (knock). At that setting, the Peak pressure is going to arrive near 4 to 6 degrees ATC After TDC. This is the sweet spot to gredge power out of the combustion, without driving the rings down around the skirt, or making holes in pistons. I love it!! Jim
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