How much do dwell changes affect timing?

[dibbons]

I have run around for a year now with the dwell in my 1972 single point 318 distributor set at only 23 degrees. Today I finally got it back within specs at 33 (factory service manual indicates a range of 30-34). I expected my idle speed to change after the adjustment, assuming changing the dwell would change the initial timing setting. However, the idle speed seems to be about the same as before, indicating to me the timing is the same or changed very little. Am I correct in my assumptions?

 

[71DodgeDemon340]

Read this on a website maybe it will help?

"At normal engine operation speeds, the points open and close a couple of hundred times per second, the exact number depending on the number of cylinders and the engine RPM. The points need to be closed for a appreciable time in order to build up the maximum magnetic flux in the ignition coil core.
The period of points closure is specified by the ignition system designer and is typically expressed as degrees of distributor rotation. In a four cylinder engine, the angle between each ignition cam lobe is 90° and the period of points closure or "DWELL" is usually a bit over 45° of distributor rotation. In a six cylinder engine, the lobes are 60° apart and the dwell time is 30° to 35°.
The dwell is adjusted by setting the points gap to a specified distance at maximum opening. A narrower gap gives more dwell and a wider gap gives less. Taking it to extremes, excessive dwell means that the points close too soon after opening, cutting off the magnetic field collapse before it delivers all its energy. Too little dwell gives the magnetic flux insufficient time to build up to the maximum.
Both conditions give a weak spark which gets even weaker as the engine RPM rises and produces misfiring at normal operating speeds. The dwell, as well as spark plug gap, do have an effect on ignition timing. The later the points open, the later the spark comes and retards the timing. The earlier the points open the sooner the spark comes and advances the timing. That is why timing is the last thing to be set in a tune-up."

 

[MoparLeo]

A four stroke engine fires every other rotation or 1/2 crankshaft speed. That is why the camshaft has 16 lobes for an 8 cylinder engine. Why are you still running a point and condenser distributor ?

 

[67Dart273]

I have run around for a year now with the dwell in my 1972 single point 318 distributor set at only 23 degrees. Today I finally got it back within specs at 33 (factory service manual indicates a range of 30-34). I expected my idle speed to change after the adjustment, assuming changing the dwell would change the initial timing setting. However, the idle speed seems to be about the same as before, indicating to me the timing is the same or changed very little. Am I correct in my assumptions?

Your timing went more retarded if you explained this correctly. Less dwell = wider gap = advanced timing

Normally as the points wear, the points gap "closes up" resulting in MORE dwell and retarded timing.

so if you actually went from 23 to 33, you retarded the timing.

I don't remember anymore, I think on a V8 at least it's a 1:1 change

 

[Abodybomber]

Your timing went more retarded if you explained this correctly. Less dwell = wider gap = advanced timing

Normally as the points wear, the points gap "closes up" resulting in MORE dwell and retarded timing.

so if you actually went from 23 to 33, you retarded the timing.

I don't remember anymore, I think on a V8 at least it's a 1:1 change

^^ What I remember, from shop class Del...

 

[Rapid Robert]

that's what I remember also, pretty close to 1-1, 1 deg dwell/1 deg timing change. You can set the dwell pretty much wherever you want it (within reason) and as said: smaller gap=more dwell time=more power (more coil saturation time)=shorter point life(more contact time so more time to burn) good for max performance bad for Grandma. (go the other way for her). (maybe bump the gap to .020"). gap/dwell and life/performance are inversely proportional. point spring tension is a consideration also as is bushing wear (radial play).