Itinerant Air-Cooled

The range for my SP is 44 to 50 degrees for new points, and 42 to 58 for used points.

What is ideal?
The top of the range? 50 degrees new, 58 degrees used?
The bottom of the range? 44 degrees new, 42 used?
Split the difference in the middle? 47 degrees new, 50 degrees used?


neal

The larger the gap, the smaller the dwell angle number, in degrees. So I like setting my new points to the low end of dwell angle, around 43°. Then, as the points block wears, the gap shrinks and the dwell angle increases; this way I get the most miles per adjustment. I usually reset the points once it gets to 50°, which for my Napa Echlin brand points, is about every 10k miles.

Note that ignition timing will retard itself over the life of the points, so if you set at 43° and wind up at 50° some months later, your timing will be slightly retarded. I think over the last 10k miles, I "lost" about 3° of ignition timing as the points block worse down.

See you at The Lab in July!
Robbie

Thanks so much. I was going to go with 50 degrees for my used points, but had so much fun adjusting them, including forgetting to take off the socket and wrench on the generator pulley when I started it, that I stuck with 44 degrees. It was at 60 degrees. And I set the timing with the vacuum hose off and blocked. Usually I don't. It doesn't seem to make a difference, maybe slightly. So now for a quick test run to see if we have better power now.


neal

ruckman101 wrote: ↑

Sun Jun 11, 2017 4:05 pm

Thanks so much. I was going to go with 50 degrees for my used points, but had so much fun adjusting them, including forgetting to take off the socket and wrench on the generator pulley when I started it, that I stuck with 44 degrees. It was at 60 degrees. And I set the timing with the vacuum hose off and blocked. Usually I don't. It doesn't seem to make a difference, maybe slightly. So now for a quick test run to see if we have better power now.


neal

You asked . . . .

Ideal dwell is best ignition coil performance which is to give it about the same time to build a magnetic field as to collapse it. Distributor rotates 360* and fires four cylinders, thus 90* total rotation time per cylinder.
Half the time closed (the dwell) is 45*. Didn't know it was that easy did you?
Colin

But wouldn't a shorter dwell time give the coil an opportunity to build a healthier spark? Or is it quicker than that and capped in terms of capacity. So 44 degrees good. Now if I just had more confidence in my carburetor adjusting skills.

But, all in all, I think I have it back and sound. Maupin bound.


neal

ruckman101 wrote: ↑

Sun Jun 11, 2017 5:05 pm

But wouldn't a shorter dwell time give the coil an opportunity to build a healthier spark?
neal

Why would that be? The magnetic field is built when the points are closed. The collapse of the built field is what makes the spark.
Colin

Bigger the field the collapses, the healthier the spark?


neal

neal - the amount of energy the coil can pickup and release is finite. It diminishes with RPM. As the RPM gets higher the actual time the points are closed is less and less. The same is true of the time that the energy comes back out of the coil. That is why modern engines use coil packs, one for each cylinder. It helps with the time issue because 1 coil is being split 1 time instead of 4, 6 or 8 which reduces the chance of saturation. FWIW the electricity and magnetism work at the same speed flowing in as flowing out (generally considered to be the speed of light - electro magnetism other than resistance in the circuit). If they didn't flow the same in both ways it would change the law of physics re conservation of energy. Some physicist will probably prove me wrong with some quantum theory but that is the general idea. In fact someone will probably explain that in quantum physics the points are both closed and open at the same time in parallel universes.

I'm getting a clearer picture. Sounds like a dwell of 45 degrees is optimum. Of course now my mind will do a bit of chewing as it tries to wrap itself around the bigger picture, quantum physics aside for the moment.


neal

Think of it like the coil is breathing... ideally it wants the same time to breathe in as to breathe out... that's the best balance of both directions.

Thanks all. The concept of dwell is much clearer now.

neal

47 deg. +/- 3
I strongly recommend Pertronix. Engine runs a zillion times better.

hambone wrote: ↑

Thu Jun 15, 2017 1:42 pm

47 deg. +/- 3
I strongly recommend Pertronix. Engine runs a zillion times better.

that would be true if the points were burned, the lobes worn, or the shaft had some wobble in it. The pertronix is less affected by wobble and wear of the shaft or bearings because while wobble affects exactly when the points open, it does not affect when the magnetic trigger passes by the sensor - just how close the trigger is. The downside is that the pertronix is a lot harder to troubleshoot and if it fails the cost to replace it is sizeable. I wouldn't automatically say one is better than the other. Just spent quite some time the last few days helping someone troubleshoot a failed electronic distributor, and then a new bad condenser on the replacement.

Every vehicle I have installed Pertronix in the past year or so has had a dramatic increase of performance that is consistent. It is very noticeable.
$70 well worth it. I have been running points for 20 years, and Bosch quality is really going downhill. I do NOT miss point gap etc. but would have continued doing so if points worked as well. Maybe it's a modern quality thing, someone told me tungsten in the points is crappy today.
Try it: take a points only VW and install the Pertronix, then drive the car.

Bob- let's do a double blind distributor test when I get to Oregon! I can't afford to just "try" a Pertronix for fun anymore. Those expendable income day job days are over...

Robbie