Mag RPM drop with electronic ign

[flightlogic]

My system is the same. When running on the Slick only... there is a bigger drop than I ever noticed with a two mag system. All plugs are new, timing checked... low hour Slick. Guess I just get used to it. The one significant change I have made in operational checks... is from the threads here posted by the Australian guy. He does the seminars on engines etc.
At the point where I am going to descend into the airport... I check mags. All leaned up and temps stable. Seems to work well.
On the ground... just a quick key flip to check for a dead system (either EI or mag) and I am on my way. Makes sense to me.

[jimbo]

Originally Posted by Bevan

Jim,

Next time do your run up as lean as it will run smooth, then check the mags.

Bevan

I thought about that and will try it and see what happens.

Jim

[tim2542]

The slight or no rpm drop when the mag is switched off is due more to the timing than to superior spark. Some systems, LSE, Electro-air are running near or maximum advance with the throttle closed, same thing happens again at altitude.
The mag is still sitting at 20 or 25. That's why the big difference when comparing to a mag.
The PMAG uses rpm as well as manifold pressure so at idle the advance will be comparable (but probably different) to a magneto. Keeping that in mind will help understand what's going on when you do a mag check.
I think when you have two different systems what's important is to know what is normal drop from each for your system when it's running correctly.
Tim

[G3i Ignition]

That?s correct on the timing curve, the low manifold pressure will map the timing to full advance 36, 40 degrees etc. BTDC. At the higher throttle settings, where the MP is close to ambient pressure, the timing curve is at base timing of the timing curve/map. If you where to leave the EI?s MAP sensor tube disconnected from intake manifold signal, You would see a very similar RPM drop between Magneto and EI. The best set up for full power is to know what your base timing is @ specific target RPM. Then set your magneto timing there.

[jimbo]

Originally Posted by tim2542

The slight or no rpm drop when the mag is switched off is due more to the timing than to superior spark.
Tim

Except I have more RPM drop when the mag is switched off.

Jim

[bpattonsoa]

My -10 is displaying the same mag drops as the -6A. Both have the same setup, Lightspeed on top plugs, mag on bottom. Depending on the age of the top plugs, almost no drop to 10-20 on Lightspeed and 100 - 130 on the mag. I quickly learned to lean when on the ground or else the mag plugs would foul badly on a long taxi. The mag would be rough on a 1700 RPM run up without leaning.

[tim2542]

Originally Posted by jimbo

Except I have more RPM drop when the mag is switched off.

Jim

And you have a PMAG right? So again it's using a timing curve based on both RPM and MP. It's running near base timing at idle and should be close to the mag, but it's unlikely they are both the same. A light speed for example will be running at 35 + in this condition. That's why they get the big rpm drop when the EI is switched off.
We don't know where you set the PMAG, if you retarded a bit like they suggest for light props, which curve you selected, or where the mag is set. So it's not surprising to have a bit larger drop from the PMAG. Mine (Slick/PMAG) does also. Try it in flight at ~9000', you will likely see a much different drop.
Tim