Dwell reading with electronic ign conversion?

[nola mike]

using a pertronix-type electronic ignition conversion, i'm curious as to what the dwell reading should be; i'm getting 20'. when i briefly swapped the points back on, the dwell was 36' and the engine speed was increased. i know that there isn't really "dwell" in the electronic, but i would think that it should be fixed at a factory value, no?

 

[Don S]

Re: Dwell reading with electronic ign conversion?

You don't have dwell on electronic ignition.
Dwell is the angle that points are closed. No points, no dwell angle.

 

[nola mike]

Re: Dwell reading with electronic ign conversion?

You don't have dwell on electronic ignition.
Dwell is the angle that points are open. No points, no dwell angle.

right, but the electronic ignition mimics the points system by providing a signal to the coil for a specified period of time, which is essentially what a dwell meter is reading. it just happens that this signal is hardwired into the system instead of relying on the mechanical points. and the dwell is the time the points are *closed*, right?

 

[Don S]

Re: Dwell reading with electronic ign conversion?

Yes, it's when closed.
You DO NOT have dwell on electronic ignition.

 

[Howard Sterndrive]

Re: Dwell reading with electronic ign conversion?

They don't publish specs, and it's not adjustable, so no point to hooking a dwell meter to electronic ignition.
I doubt a dwell meter can read the PWM accurately anyway.... probably need an oscilloscope on 5KHz resolution to see what that module really does with the coil (-) terminal.

 

[Bifflefan]

Re: Dwell reading with electronic ign conversion?

Just put the Pertronix back in and forget about it.

Recheck and set the timing, and then set the idle to spec.

When your using points, you set them to the proper dwell using the meter, you dont install them and the read what the dwell is then call it good.
You stated you had 36 deg, but for what engine? A 4 cylinder is not the same as a V8 and so on. Dwell also affects timing and this may have caused the faster idle.
You have to set the dwell, then the timing, then the idle speed.

 

[Robj]

Re: Dwell reading with electronic ign conversion?

Adjust the air gap between the sensor and the magnet. You will find that the dwell does change a bit. It certainly did on mine. I think I am running a bit more gap than recommended and that increased my dwell. Try experimenting a bit and see where it gets you.

Have a great day

Rob.

 

[Don S]

Re: Dwell reading with electronic ign conversion?

Adjust the air gap between the sensor and the magnet.

You can't adjust dwell without points. You might be getting a reading on a dwell meter by changing the air gap on the sensor, but it's a meaningless thing to do.
The specs give you an air gap that is measured with a feeler gauge. NOT a dwell meter.

 

[Robj]

Re: Dwell reading with electronic ign conversion?

Sorry but I did use a dwell meter to check the dwell with my electronic ignition, I believe I gained about 5 degrees. I have the Ignitor I. I would suggest trying it yourself with a dwell meter and open up the air gap and see how it effects your dwell. I was having a problem running above 4000 rpm and thought it may be caused by the electronic ignition, ie not enough dwell. In the end, the 5 degrees gained was not noticed in engine performance and the electronic ignition was not the cause of my problem.

The Ignitor is just basically a switch that opens and closes as the magnets on the distributor shaft rotate by the pick-up. So by adjusting the air gap, you can somewhat control the time the switch is open and closed.

Have a great day,

Rob.

 

[nola mike]

Re: Dwell reading with electronic ign conversion?

seems like maybe my question isn't clear.

again, i realize that there isn't "dwell" with an electronic ignition. however, the dwell meter isn't actually measuring the angle through which the points are closed. it's measuring the percentage of time that it's seeing continuity--ie, it's measuring the duty cycle of voltage to the coil.

HOWEVER, the electronics should be mimicking the ideal dwell at all times, and supplying the coil with an ideally switched voltage--this is the benefit of the electronics, that the timing/strength of the signal won't change like points will when they wear.

that being the case, why isn't the signal picked up by the dwell meter the same with electronics as with perfectly adjusted points? in other words, does the dwell determine just the timing of the spark (in which case points should equal electronic dwell reading), the strength of the spark (in which case the dwell reading would be irrelevant), or some combo? i'm curious if others have different readings with their units than mine (i'm using a mallory ignition).

 

[rodbolt]

Re: Dwell reading with electronic ign conversion?

dwell angle is just that and its measured in degrees of rotaion.if its 36* it simply means that for 36 degrees of rotation the points are closed.remember the cam and dist shaft rotate at 1/2 crank speed.
if dwell angle on an 8 cylinder single point system is set at 45* the points never open.
just to open and close the points is going to take about 25* of arc,if the dwell angle is 20*and the point open to point closed is 25* thats about 45 degrees,do it 8 times and the dist has rotated 360* and the crank 720. all eight fired.
the petronix is simply a hall effect device triggering a transistor switch(ignitor) fairly simple and have been around since the 70s by various names.
still only half the system a delco EST is.
petronix still relys on the mechanical advance.
there were a few early systems that used transistor switched by low voltage points.
used about 2 volts on the points to switch coil primary current.