Lotus Elan

making a "dwell" measuring kit?

PostPost by: h20hamelan » Thu Jul 22, 2021 1:32 am

There should be a small groove in the end for reading off from the degree scale (rotor). The base has a scale. This has to be transparent showing the markings.

The base could have a cut out for a Pertronix/Accuspark module, but maybe not as important.

Anyone have some time & a 3D printer?

A3AB0AE9-DA39-494D-98B5-DFFD3819C8DA.jpeg and


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PostPost by: Andy8421 » Thu Jul 22, 2021 5:33 am

Dwell is only meaningful for points based ignition, and refers to the period in degrees that the points are closed. For an electronic ignition, this is a function of the control circuitry in the ignition module.

Could you explain what you trying to achieve, and I may be able to help?

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PostPost by: h20hamelan » Thu Jul 22, 2021 1:42 pm

ah, I will try
I had thought even with electronic which it seems most run, the "dwell" was most important for flutter or bounce.
It seems more slow and possibly exact for getting angles.
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PostPost by: billwill » Sat Jul 24, 2021 12:50 am

Electronic systems don't bounce or flutter, or at least they should not. If they bounce or flutter there is something wrong.

~~~

Dwell angle is just a rather crude method for mechanical distributors to provide the time period during which the inductance of the spark coil (i.e. the magnetic field) recharges itself, ready for it to blast into a spark at the appropriate time.

Since the inductance of the coil is a fixed static item, the recharge time should ideally be a fixed period of time; any current flowing into the coil outside the charging period is just wasted energy.

A fixed charging period is only easily created by using electronics in a control box.

With a mechanical distributor, using dwell angle to determine the charging time, as revs increase the charging time gets shorter & shorter until the coil's magnetic field doesn't fully develop, resulting in weak sparks at high revs, just what you don't want.

With an electronic controller & corresponding fixed duration 'charging' interval, eventually as engine revs increase, the interval between sparks becomes the same as the ideal charging period, so they overlap each other, the next spark triggers before the coil is fully charged, so the result is weak sparks at high revs, just what you don't want.

The only cure would be a coil that charges more quickly. Or as usually happens with fuel injection, you have one coil per spark plug, so it has two full engine revolutions in which its magnetic field can charge up.
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PostPost by: billwill » Sun Jul 25, 2021 1:09 pm

Oh as an aside, before anyone else jumps in with it.

It seems that most multi-coil systems actually fire the spark once per revolution as this is simpler to do. This means of course that every other spark not useful, (though it does not harm the system) because the cylinder of the engine with that sparkplug will not have an appropriate fuel+air mixture in it at the time; both valves are probably open.

For this reason these are known as wasted spark systems.
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PostPost by: Andy8421 » Sun Jul 25, 2021 6:14 pm

Bill,

I think that modern COP 'coil over plug' systems fire the plugs individually, which allows for individual cylinder timing.

The wasted spark systems were previous generation, typically with a central coil pack with plug leads to the respective spark plugs. The pack would fire two plugs simultaneously, with the spark on the plug approaching the end of the power stroke wasted.

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