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Mag RPM drop with electronic ign

M

mcattell

Well Known Member
I have the Light Speed Plasma II on the right mag and a standard Slick mag on the left. During run-up I'm getting a higher than usual RPM drop on the Slick mag. In reading the Light Speed manual I see this is to be expected because with both selected on the key switch the RPM would be higher than with two standard mags. Therefore the RPM drop with the Slick would appear to be higher than if you had two standard mags. So my questions is, what kind of RPM drop are others getting with their Slick mag with the same setup?

With only the electronic ignition selected at run-up the RPM drop is barely noticeable. Very impressive.
 
Eci 0360 with PIII on right--Slick on left.

1600 rpm/full rich

Mag off line -- 10-20 rpm (or less) drop

EI off line 60-70- rpm drop.

Cheers,

db
 
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I had the same setup as Dave and had exact same behavior.. 10-20rpm on EI and typically 70rpm drop on mag.
 
no drop on EI only

I have a light speed plasma II on the left, slick mag on the right.
Mag off, I get no drop at all at 1900, full rich.
EI off, I get 40-60 drop.

The timing of the light speed at run-up conditions is almost 40 degrees btdc, and that flame front has burned a long way before the mag even fires at 25 degrees, so you would not expect to get much drop at all by turning off the mag.

If you are getting much of any drop with the mag off, verify the timing on your light speed.
 
Run-up at 1800 rpm,

Mag off, 10 -20 rpm drop

EI off, 100-120 rpm drop

Key switch, YO-360-A1A
 
This brings up an interesting modification. What if you were to make a clutch that could go between the mag and the drive so that after checking it you could "put it in neutral" to save wear and tear on it until it was needed.
I have dual Plasma 1s with the interconnect so that if you switch one off the other advances about 5 degrees to restore power. It's interesting when you do a check that when you turn one off, the rpm drops about 70, then after a short delay for an internal time-constant, comes back almost to the same rpm!
 
Superior XP-360 (IO360)
Plasma II on top plugs
Slick Mag (Impulse) on the left and bottom plugs

Run-up 1800 RPM:
Mag OFF - 20-30 drop
Elec Ignition OFF - 100-120 drop
 
Mag drop not as expected

I have a TMXO-320 17 hours on engine
160 HP. Carbureted
Slick mag on L
EMag on R. (P model 114 running A curve) With NGK Iridium auto plugs suggested by EMag and gapped at 0.030

Run up 1700 RPM. Full Rich. Elev 960
Mag offline EMag online. drop 90
EMag offline Mag online. drop 40

I would think I should have a lesser drop with the EMag online (after all isn't the EMag spark is supposed to be a higher intensity and offer some advance spark at that speed). Checked my switch wiring and the P leads are routed and labeled correctly.

Can someone explain why the RPM drop is more when EMag is online?

Jim
 
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.
 
It's the advance

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
 
Timing

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.
 
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.
 
PMAG

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

Jim
Click to expand...

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
 
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