lars

The C1/C2 Forum got into a lengthy 9-page discussion on this subject matter. You can read the whole thing here:

https://www.corvetteforum.com/forums...post1593766803

But if you just want a summary of the factual findings of the relationship between Dwell and Timing, I summarized it after some testing in post #175:

So here is the final summary of everything discussed and determined. I just fired up the test engine this morning and took some last measurements and made some observations:

Set up and ready to fire it up with dwell meter and feeler gauges:


Dwell meter verified calibrated at 45 degrees with engine not running:


Engine running. I like to run a little more than 30 dwell on my own engines, but I backed off this 31.5 reading to 31 degrees for the meaurements to be taken:


I can't remember the last time I actually checked point gap with a feeler gauge, but I did it this morning:

Final Results and Summary:

• You can make minor timing adjustments using the dwell adjustment screw.
• 1 degree change in dwell changes timing 1 degree.
• Turning the screw IN (clockwise) INCREASES dwell and DECREASES timing.
• Turning the screw OUT (counter-clockwise) DECREASES dwell and INCREASES timing.
• Turning the screw 1/8 turn changes dwell and timing by about 3 degrees.
• .019" point gap = about 31 degrees dwell.
• Increasing point gap decreases dwell and increases timing, and vice-versa.
• A 2 degree change in dwell changes point gap by .003", so every .0015" change in gap changes dwell and timing by 1 degree.

Lars

Big2Bird

Lars, right to the POINTas always. Your TIMINGis perfect. No DWELLINGon the subject, just a CONDENSEDversion CAPPEDso as to notIGNITEnor INDUCEfurther arguements.

'75

Nice write up.

jnb5101

I would have thought that each degree of dwell would cause two degrees of crankshaft timing.

mrvette

I won't dwell on this point, as my computer is advanced......

carriljc

I'm so glad not to do that anymore...

lars

That was my initial reaction, too, since there is a 2:1 relationship between distributor degrees and crankshaft degrees (dwell is the number of camshaft degrees that the points remain closed). However, if you, for instance, decrease dwell by 1 degree, the dwell is decreased 1 degree by opening the points 1/2 degree sooner, and closing them 1/2 degree later. It's only the opening point that counts for triggering timing, so that 1/2 degree earlier opening changes timing by 1 degree. Therefore, a 1 degree change in dwell changes timing by 1 degree. If you changed the opening point by 1 degree, the timing would be changed by 2 degrees, but this would cause a 2 degree change in dwell - not 1.

Lars

MelWff

thanks for the summary. I started following the C1/C2 thread on the topic but eventually gave up on all the back and forth going on.

Paul L

My antique...still works.

jnb5101

Lars, thanks for the explanation. It makes perfect sense when you think about it.