The Stovebolt Site Forums The Shop Area Engine Shop Dwell Tachometer Recommendation

Hi All,

For a standard ignition system (6v or 12v, stock coil w/ points in a 216) is an analog tachometer preferred or a digital multimeter/tachometer?

My concern is that a digital meter may be too erratic to read where an analog meter is somewhat "self-filtering".

Model recommendations are welcome too.

Thanks!

Bill

I use the cheap Actron dwell/tach. Works fine.

You can find them online pretty easily.

Here's one for $35.

Sears - Actron Dwell/Tach

Analog is definitely the way to go. A dwell meter is actually a voltmeter with a different scale. With the points open, the dwell meter sees full battery voltage because no current is flowing. With the points closed the only voltage the meter sees is whatever voltage is needed to push the current through the points (very small unless the points are dirty or burned). The "dwell" is the average voltage between points open and points closed, and it changes as the point gap varies that time span. The best dwell is about 66%, points open 1/3 of the time. On a V8 that's 30 degrees of a possible 45. On a 6 cylinder, it's close to 40 degrees, as the total dwell available is 60 degrees between the cam lobes. Digital meters respond to voltage changes so quickly that the readout can become unintelligible gibberish.
Jerry

Jason and Jerry,

Thanks for the input and the explanation. Looks like analog is the way to go.

Best regards,

Bill

I got a Dwell/Tach from Sears. Not expensive and it has worked just fine. It is very helpful when trouble shooting points from under the hood. And it works just like the book specs say it should.

What about for a standard 6v ignition system?

If a regular dwell meter doesn't want to work on 6 volts, it's pretty simple to check dwell with an analog voltmeter. With the engine running, check the voltage at the coil + terminal, grab the calculator and figure 33% of that figure.

For example: Voltage at the coil + terminal = 7.3 V

7.3 X 0.33 = 2.40 V Adjust the point gap until the voltmeter reads 2.40 V. at the distributor side of the coil (engine running). The dwell will be 40 degrees.

Jerry

That is amazing. I would have never thought to do that. Thanks Hotrod