dwell vs timing

[356robo]

Book says changing dwell changes timing but does'nt say which way. How does changing dwell change timing? If I increase dwell, does advance increase or decrease?

Thanks in advance, (no pun intended)

Rob
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[Mudi]

increase dwell = decrease point gap = decrease advance in timing..

[356robo]

Thanks Bob,

I'll regap the points a little closer and hopefully get the advance down a little. Right now, its at 4' Atc and about 34' btc at 6,000.

Rob

[MrJTP2001]

In a basic ignition system (non-electroinc) dwell is the amount of time the points are closed. While the points are closed the coil is storing energy in the form of its magnetic field. If dwell is too short you might not get the correct amount of energy stored up in the coil which results in a weak spark.

The spark occurs when the points open (and the stored energy in the magnetic field collapses)

In basic ignition systems you should set the dwell per spec before you set the timing. Get the dwell set so that it maximizes the energy stored up before the points open and the spark occurs.

A normal timing light will trigger of the leading edge of that spark. I won't go into what is going on during the spark.

So if you set the dwell, then the timing you should maximize the energy in the spark and have the spark occur at the correct time.

In some basic ignition system this is an iterative process so always check the dwell after setting the timing, correct it if needed and repeat.

[911pcars]

Thanks Bob,

I'll regap the points a little closer and hopefully get the advance down a little. Right now, its at 4' Atc and about 34' btc at 6,000.

Rob

Rob,
The other way around. Adjust the point gap (dwell) first. Then, with a timing light connected to the system, adjust the ignition timing by rotating the distributor housing. There's a one-to-one relationship between dwell angle and ignition timing.

Sherwood

[orange911]

Rob,

If you can recruit someone to crank the car (with cap off) and you stay back to adjust. You can get good dwell numbers with cranking rpm. You won't have to walk back and forth or remove/reinstall the cap.

[68911+1]

There's a one-to-one relationship between dwell angle and ignition timing.

Sherwood

So you are saying that 1 degree of increased dwell equals 1 degree of decreased timing (or the inverse)?

Never too old to learn. You would think after 42 years of setting points I would have known this was a 1:1. Thanks.

[911pcars]

So you are saying that 1 degree of increased dwell equals 1 degree of decreased timing (or the inverse)?

Never too old to learn. You would think after 42 years of setting points I would have known this was a 1:1. Thanks.

If the dwell time increases 1 degree (e.g. 29>30º), the ignition timing decreases an equivalent amount.

Thus with normal rubbing block wear, the point gap decreases, dwell time increases (no. deg. points remain closed) and ignition timing decreases.

Sherwood