The Dwell


#1

My son & I were at a cruise night the evening & looking at one particular car I pointed out the label in the engine bay that identified the timing, spark plug gap and the dwell. My son immediately asked me what the dwell was & I drew a blank. I use to know this stuff back in my teens but I drew a blank. So I ask the experts; Can you explain what dwell is in layman’s terms



Thanks for the help.


#2

The dwell is the number of degrees of distributor movement the points remain closed (at least I think it’s closed), so it’s directly related to the point gap. Set the dwell correctly, and the point gap is correct.
Here’s a more detailed explanation:
http://autorepair.about.com/library/faqs/bl483h.htm


#3

At the instant the points open the current in the coil is interrupted and the spike of voltage for the spark is created. Before the points open they have to be closed for a while to allow the coil current to build up. That period is the dwell, generally expressed as a number of degrees of crank or distributor rotation. It’s called dwell because that’s the only time the points stand still. Dwell time becomes important at high RPM’s because the time to build up current for each spark becomes significant. Dual point distributors have two sets of points in parallel with staggered dwell periods, so the total dwell is extended beyond what a single set could do and still have the points open quickly enough at spark time.