What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

pmag RPM drop

W

William B.

Member
My IO 375 with auto plugs and leads, dual P mags, now with 36 hours.
During Mag check at 1750 rpm I get 100 rpm drop on one side and 50
on the other. Checking at Higher RPM 1850 the drop shows 80 rpm and 40 on the other. My understanding was there was to be very little mag drop with
these Pmags? Anybody with knowledge on this please comment.
 
Maybe Bill can check with the manufacturer and get back to us on this? I'd like to know also.
Never had any drop with the lightspeed, when it worked...:eek:
 
Do you have top and bottom plugs per pmag? My experience is that when bottom only I get more of a drop than top only. The bottom plugs tend to foul more. Also, be sure to lean out for ground ops. Running to rich while taxiing well foul the plugs quickly too.
 
miyu1975 said:
Do you have top and bottom plugs per pmag? My experience is that when bottom only I get more of a drop than top only. The bottom plugs tend to foul more. Also, be sure to lean out for ground ops. Running to rich while taxiing well foul the plugs quickly too.
Click to expand...

Ryan has some good advice.

Some mag drop is normal with the P-mags.

"flyingriki" comment regarding no mag drop on his LSI, when it worked, is probably a result of how the two different ignitions are designed. Remember, the P-mags use the cam gear to set the timing and we have found that there is about 1.5 degrees of gear lash (slop) in that setup.

Other things that could impact your mag drop is the plugs used (solid vs. threaded cap), how the wires are run (touching and engine mount), how you grounded the P-mags (engine case vs. forest of tabs), etc.
 
Thanks Ryan

I will switch tops for bottoms on each side and see if the issue follows.
miyu1975 said:
Do you have top and bottom plugs per pmag? My experience is that when bottom only I get more of a drop than top only. The bottom plugs tend to foul more. Also, be sure to lean out for ground ops. Running to rich while taxiing well foul the plugs quickly too.
Click to expand...
 
Bill,
For a data point I have a TMXO360 with dual pmags. Each mag is wired to top and bottom.plugs I get 50-60 RMP drops on each mag at 1700 rpm

Mike
 
G3i Ignition said:
Interesting on above "quotes"
So how far are the left and right P-mag ignitions out of sync. even on best set-up?
Spark plug terminal ends, really?
Click to expand...

We found that even standard mags have up to ~1.5 degrees of slop in them. This can be made worse depending on how one sets the timing. (It is best to set the TDC on both P-mags at the same time. Don't ask me why but we have had customers report minor timing divergences when they are set individually.) It is nothing a pilot would ever notice but with the EICommander installed, it will pick up the difference.

Regarding the sparkplug ends; again, the EICommander has picked up a slight variation due to plugs with screw on caps.

In fact, the EICommander can tell me when my plugs are getting close to needing replacement.

To be clear, individually, you might never notice all these things, but toss in an EIC and you will "see" them. Heck, one customer kept getting Timing Divergence Alarms and once he moved the P-mag ground wires from the firewall to the engine case, they went away.
 
The EICommander is the best thing to ever happen to Pmags. It's like an engine monitor for your ignition.
 
FasGlas said:
The EICommander is the best thing to ever happen to Pmags. It's like an engine monitor for your ignition.
Click to expand...

Thanks!

I really wish we could connect to other ignitions and report on their health as well. But due to different architecture and timing curves, we are limited to the P-mags.

BTW, I will be giving a presentation on timing and the EIC at Oshkosh this year. We hope to go back-to-back with Brad from Emag.
 
N941WR said:
Thanks!

I really wish we could connect to other ignitions and report on their health as well. But due to different architecture and timing curves, we are limited to the P-mags.

BTW, I will be giving a presentation on timing and the EIC at Oshkosh this year. We hope to go back-to-back with Brad from Emag.
Click to expand...

Maybe you can talk Ed into coming out to Osh this year. I'll be there in the Lancair (with my EIC). Hope to run into you while I'm there.
 
FasGlas said:
Maybe you can talk Ed into coming out to Osh this year. I'll be there in the Lancair (with my EIC). Hope to run into you while I'm there.
Click to expand...

He said he is too old go to OSH. I invited him to join us on the two day drive and then spend a week in our camper with my six year-old and for some reason he declined.
 
Hey, Bill, what is a "normal" drop on the pmags for a 320? I have a buddy doing early testing and he reported 100 rpm drop yesterday on each mag (same drop, but concerned about the magnitude).

Thanks,
Greg
 
Greg Arehart said:
Hey, Bill, what is a "normal" drop on the pmags for a 320? I have a buddy doing early testing and he reported 100 rpm drop yesterday on each mag (same drop, but concerned about the magnitude).

Thanks,
Greg
Click to expand...

No idea, I have an O-360. Many things can impact the drop; from sparkplugs, the age of the sparkplugs, to the position of the plugs, how they set the timing on the P-mags, to the type of plug wires used. My drop changes because I'm always playing with something. I typically see between 50 and a 100 RPM.

That and I do my run ups at 1400 RPM because I fly off of grass.

I always wonder about people who say they don't see any drop. I could see that when someone has both an EI and a traditional Mag or two different types of EI's. The reason is that in a mixed environment, one of the ignitions is going to fire first and turning off the lagging ignition won't make any difference.
 
I'm running 2 Pmags with NGK extended tips on top and Champion REM38S on the bottom, all gapped at ~ .032. Taylor wires, resistors at or below 5K for the Champions and 6.5K on the NGK's. EICommander shows 2.0 degrees differential between the Pmags. RPM drop @ around 1700 RPM's is about 80'ish. This is a fresh setup. Prior was REM38S on both top and bottom with much less RPM drop. It's obvious that different plugs will react differently on RPM drop. In this new setup the NGK's extended tip will fire the mixture a fraction sooner than the flush tip 38S's. Every setup will have a different result. But I would be suspicious of problems if the drop was excessive or rough on either ignition.
 
N941WR said:
...I always wonder about people who say they don't see any drop...
Click to expand...

I experience no drop as displayed on the GRT EFIS (10 RPM resoloution) with dual 113 PMags on a 200 HP Lyc. I check at 1700 RPM and lean to max RPM for the EOR check. I can hear a slight difference in tone when single mag and I do get the noticable EGT rise, but the RPM does not change. I also do the "real" mag check in cruise and LOP, so I know the mags are shutting down when commanded. But Zero drop on the ground.

OTOH, my 180 HP injected Lyc would routinely show 50 RPM per side with dual 113's.
 
FasGlas said:
...EICommander shows 2.0 degrees differential between the Pmags....
Click to expand...

Because of the geartrain slop mentioned earlier, we set the EICommander up so it starts at two degrees. We found that some of our early customers would get concerned when they saw their timing bouncing around below that threshold.
 
You must log in or register to reply here.
Back
Top