High Pmag RPM drop?

[Jeff R]

I have both a PMag and Slick, using BR8ES auto plugs for the PMag. At 1700 RPM, the drop of the PMag is slighty worse than the Slick, about 120 for the PMag and 110-110 for the Slick. From what others have said, this drop for the PMag seems high. I am using the B curve, which is recommended for new engine breakin. I have the auto plugs on the upper left side and lower right side.

Should I have them both on the top or on the bottom? Should I try the more expensive plugs? Any other ideas?

[GeneL]

Originally Posted by Jeff R

I have both a PMag and Slick, using BR8ES auto plugs for the PMag. At 1700 RPM, the drop of the PMag is slighty worse than the Slick, about 120 for the PMag and 110-110 for the Slick. From what others have said, this drop for the PMag seems high. I am using the B curve, which is recommended for new engine breakin. I have the auto plugs on the upper left side and lower right side.

Should I have them both on the top or on the bottom? Should I try the more expensive plugs? Any other ideas?

Try going thru the timing procedure again. I have been told by those in the know that the electronic mag plugs should be on top for the most benefit and smoothness. Gene

[Omega232Devils]

Jeff,

Disclaimer: (I have 4.9 hours on my dual PMags as of today), however I had a Jeff Rose EI and Slick impulse mag setup before that. My RPM drop on the split system was 10-40rpm when running EI only and 90-110 when running Magneto only. This was mainly due to the efficiency of the EI system and advancing spark carrying most of the load even with both systems on.

My dual PMags on A Curve (Jumper in) was 100rpm drop on each PMAG. Running on B Curve (Jumper out) it was 80rpm drop for each. (only one flight on B curve so far)

I talked to Brad at EMagAir regarding the drop in RPM and he stated that it depended upon your engine and you need to establish a baseline. Then note any changes to that baseline. Use the search function and you will find some great knowledge about what you are trying to determine during a "Mag check" and how/why to do one at altitude.

As for your auto plugs, I have always ran my auto plugs on the bottom as they are the ones that tend to foul easier. The hotter spark of the EI helps prevent fouling of plugs.

I am sure smarter people than I will jump in here shortly.

Dan

P.S. I am not sure the "B" curve is better for engine break-in. From the EMagAir114v20 Install Manual "The ?B? curve will allow timing to advance (typically) as much as 39 degrees. The ?A? curve will allow timing to advance (typically) as much as 34 degrees. We recommend starting with A curve.

[Jeff R]

Oops, I am running the PMAG with the jumper installed, so I am actually running the A curve.

[Andy Hill]

EI should give you a significantly lower Mag Drop - my experience is ~30-40RPM. However, to get this requires the optimal "burn" the EI should do - and in order to do that it needs:

1. Correct Mixture
2. Correct Baseline Timing
3. Correct MAP sensing

So for now I would suggest recheck the timing setup as per PMag instructions, and confirm the MAP line is connected and clear.

[penguin]

Originally Posted by GeneL

... I have been told by those in the know that the electronic mag plugs should be on top for the most benefit and smoothness. Gene

I've been running an E/P-Mag for 8 years and have found no real difference where the plugs are. The position of the plugs fired by the P-Mag certainly would not give you the mag drop you are seeing, which is higher than usual. My experience is the same as Andy above.

As the others have said I would ensure the timing is at top dead centre, and would stick my finger in the spark plug hole on #1 cylinder to make sure it is at TDC - gently rock the engine to ensure the piston is at the top. Also make sure the manifold pressure line is tight. Running with the jumper will be fine for now.

Pete

[Jeff A]

Wanted to see if anybody had any updates or further suggestions for a high RPM drop during the mag (P-Mag) check. Here's my situation:

I have a Superior IO-360 with two new P-Mags, their harness and NGK BR8ES 5422 auto-plugs. I (mistakenly) did not install the jumper, so I started using the 'B' curve. Setup and timing was otherwise performed as described in the P-Mag manual. Initial engine ground runs in May showed a 100-120 RPM mag drop on both sides. After reading other posts I decided that may not be too uncommon, so elected to perform the first flight(s) as is.

After 5 hours, I performed the first oil change and decided to try and adjust the timing. I checked the plugs and performed the timing procedure again just to make sure everything was okay. I also installed the jumper on both P-Mag plugs, putting both on the 'A' curve. The MAP tubes are obviously clear because I was able to time both P-Mags at the same time, and the MAP gauge is functioning normally. During the leak check and run-up, I realized the RPM drop had gotten worse. Both mags were now showing an initial drop of nearly 200 RPM, and would stabilize at 170-180 RPM drop. The mag drop was check at 1700 & 1800 RPM....no difference. I did not attempt a higher or lower test point.

Any suggestions out there? Should I simply remove the jumper and be happy with the 100-120 drop? At what point do you say the RPM drop is TOO much and not continue with the run-up and flight?

I WILL e-mail/call E-MAG this week, but wanted to see if anyone out there could share their opinions/fixes/comments. Thanks.

[petehowell]

One data point - I have found that my Pmag drop varies based on how well I have leaned the mixture at runup. If I have aggressively leaned, drop is much less than if I have left the mixture rich.

My field is a at 900ft MSL. No idea if this is pertinent, but thought I would toss it out there. I have an Emag and Pmag, so no ability to compare to a mag. My B-curve is custom set aggressively to facilitate LOP cruise ops.

[Jeff A]

This being a new (expensive) engine, I guess I haven't given much thought to leaning during taxi and run-up. As I'm not a engine expert in anyway, and I'm pretty paranoid about doing anything that will cause any type of damage. I've been careful to follow Barrett's and Superior's break-in instructions, and haven't touched the mixture except for start-up and shut-down.

I'll have to try a few more things next time I get out to the hangar. Any tips on proper taxi and run-up leaning? I'm guessing a search will reveal quite a few opinions.....

[SMO]

This doesn't answer your question, but I have a Pmag and a Slick on an IO-320 from Aerosport. ~100 hours on the engine. I get 120 - 140 drop on both sides. Always been that way. That is my baseline and unless there is some change I am happy with it and go flying.