The term "dwell" is very accurate, when the information is broken down into understandable terms. There are 360 degrees in a circle, and when the points are closed, they "dwell together". If 360 degrees of distributor rotation is divided by the number of cylinders, there's a possible dwell of 60 degrees for a 6-cylinder, 45 for a V-8, 90 for a 4-cylinder, etc. The magnetic saturation of a coil is best at about 66% dwell, which would be 30 degrees for a V-8, 40 degrees for a six, etc. A lot of the oscilloscopes I grew up using for engine diagnostics rated dwell in percentage instead of degrees. If a dwell specification or point gap isn't available, the 66% rule works very well. BTW, changing dwell one degree results in a 2 degree change in ignition timing, since the crankshaft turns twice the speed of the distributor. Close point gap (long dwell) results in late timing.
Jerry
Last edited by Hotrod Lincoln; 10/15/2010 1:09 PM.
