Back to the post #42. I alluded, if the timing light incorrectly triggers on the start of dwell instead of the ignition event timing could appear advanced, and advancing with RPM.
I did some estimates, based on two RPMs, and a fixed dwell of 2.5 ms. The dwell on HEI strives to charge the coil to a peak current value. The inductance of the coil is in the relationship, for how long it takes to reach the peak current. More inductance, longer time. The 2.5 ms is an estimate, the actual number might be between 2 and 4ms.
At 700 RPM the time between cylinder events can be calculated. First calculate the frequency of spark events. There are four spark events per engine rotation, so 700 x 4 is 2800 spark events per minute. By dividing by 60, the frequency is 46.7 Hz (cycles per second). Time is the inverse of frequency, so 1 divided by 46.7 is 21.4 ms. So the engine rotates 90 degrees in 0.0214 s. I suppose you wonder about 90 degrees? one revolution is 360, there are 4 ignition events .... 360/4 = 90. So back to the top. What if the timing light triggered on the start of dwell, that happens 2.5 ms earlier? That can be estimated, 90 x 2.5/21.4 = 10.5 degrees advanced from ignition event, as seen by light. So what happens at 2500 RPM? 90 degrees rotation is 6 ms, so 90 x 2.5/6 = 37.5 degrees. When timings are compared at 700 vs 2500 there is a difference of 27 degrees. That is what appears, but these estimates are for the condition that ignition event timing is fixed.
If timing appears wrong, and timing is adjusted to that, by the light, the engine may really run poorly..... Some of us might guess what is up, by cracking the throttle, and listen what happens.
So possibilities for false trigger, could be timing light clamp probe polarity, or ignition coil wiring incorrec
Why might the Mopar ignition be different? It may have been wired correctly. Or because it does not use active dwell control. It uses a ballast resistor, the dwell period is long, and energy wasting.
