Piston Slap: Dwelling on Ignition Timing
Hagerty Community Member Jeepcj5 writes:
I’ve successfully (at least in my mind) set point gaps and timing in various cars. The reason I say successful is because they seem to run well afterwards. I have a dwell meter that I’ve been told to use, but I just don’t understand it or what it’s even telling me.
How does dwell come into play? Should I not worry about it? If I do need to worry about it, can you explain it in a “Dwell for Dummies” sort of way?
This applies to me, as I am clearly a dummy when it comes to dwell or any other aspect of mechanical ignition systems. I (poorly) define dwell time as the time it takes to make a good spark, but Denso properly defines it as “The period when the ignition system applies an electric current to the ignition coil’s primary winding.”
Dwell time and dwell angle is adjusted on mechanical ignition systems with hand tools, a feeler gauge, and dwell meter. You can’t do much on any vehicle after 1975(?), as electronic ignitions became standard fare. (Vehicles from the 1980s and newer can be tuned with a computer and software, but that’s irrelevant to this discussion.) No matter the ignition system, this concept is important because an ignition curve is crucial to efficient combustion.
Perhaps Jeepcj5′s experience proves that you don’t need to mess with dwell time (i.e. the part of the process that needs a dwell meter) very often, but that’s between an owner and their fuel economy calculations. And the sensitivity of their butt dyno, but now we’re really getting off the rails.
Ignoring dwell time and only using a feeler gauge for your points (i.e. dwell angle) is basically approximating your ignition timing. And since graphics and videos are better at this than my wordsmithing, let’s try a couple of selections from YouTube. Here’s a fun retro video on the concept of dwell angle.
And the video below is a solid example of how to set dwell angle and dwell time, among other bits of knowledge for analog ignition tune ups. I’ve started it at the part relevant to dwell time, but you might want to watch the whole thing. Stick around for the 10:15 mark, as Uncle Tony’s Garage rightly suggests, “It’s not rocket science, right?”
The only issue I have with analog ignition systems is the availability of quality-made points in our modern times. Condensers in the ignition system have the same issue but to a lesser extent, as they are generally more durable. If you can still get good quality points/condensers for your application, adjusting your dwell time can improve your vehicle’s performance over the long term. If you cannot, maybe it’s time to convert to electronic ignition.
So give it to me, Hagerty Community: What did I miss in this discussion of dwell time? I am far from an expert in this matter, and your feedback will only make this article better.
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