Dual PMAG vs. One PMAG

For those who transitioned to PMAG, one at the time, I was wondering how much of a gain/change (if any noticeable) did you experience?

In another word, is it worth $1500 bucks for a person that does not pick up his money on a tree?

Thanks in advance

I have an Electroair and one mag. Can turn the mag off and see little to no difference in flight. I vote for going with dual PMags. That is what I'm putting on the RV8 build. Dollarwise, a new mag with gear and wires will run you about the cost of the PMag and then you'll add another $800 or so at 500 hours when it is time to replace it so really the PMag is less costly.

If you are trading in mags for PMags, dont forget to factor in the money from the sale of your mags. That may make the decision a little easier. There are always people looking for standard mags, so you wont have a problem selling them.

As for your question, you wont notice much gain from a dual setup over single, but factor in mag overhaul cost and auto plug versus airplane plugs and you can get closer to justifying the second PMag.

Dan

My 2cents, I went from single mag and electroair to dual Pmags and am happy with the decision.

I originally bought two pre-loved P-Mags and installed them one at a time to make sure they had no defects.

The change to one P-Mag and one Mag was great, installing the second I found amazing.

My aim was to be able to run LOP, the first P-Mag allowed good leaning but eventually a slight roughness would occur, with the second P-Mag I can aggressively lean and it's smooth all the way to engine shutdown.

Definitely worth it in my opinion.

Also why would you want to run two different ignition timings, one variable and the other fixed at 25 degrees?

Cheers

I've used Bendix mags, Slick mags, Electroair and now dual Pmags. In my subjective opinion, you get 80% of the "goodness" from one Pmag. 20% with the second.

I'm definitely a pilot on a budget, so I bought the first and flew a year before buying the second the following year.

Also saved a fair amount of weight with the Pmag. Maybe 2 lbs per side.

A few years ago at Osh I ask that question and I believe Brad said with one P-mag you would get about 70% of the advantage on one.

If one is good, two is better (as long as they are independant of each other which they are).

Bevan

I agree with the notion that two ignition firing at the same time it is better than otherwise and also I do see the benefit of PMAG compared to MAG though not as pronounced as some folks have experienced, perhaps my slick mag is functioning extra good.

I have my slick MAGs for sale as a package and if I find a buyer, I will switch but it does not seem the difference is worth the $$$ if I was going to pay that strictly from pocket, which comes out of my gas money and it would take years to make up for the gas saving that comes with PMAG.

I installed one pmag last june. took but a few hrs as promised. seemed to run fine and a week later I flew from OR to OH, seeing 10+% improvement on fuel economy as well as a drop in EHT and rise in CHT [meaning more power is being produced]. my plane now starts almost immediately.
years ago I had a jeff rose system which ran fine for several years. then one day it quit. that's when I liked having the slick mag, fat, dumb, and happy, still firing away at 25°, oblivious that anything had changed. with the jeff rose I had a gauge showing advance. rarely can you achieve a large spark advance, typically just a few degrees.

The 75/25 ratio is a sound bet if you are trying to simply do a cost analysis for fuel savings. However, keep in mind that dual plugs are not there for redundancy- they're there to allow the flame front to get all the way across the piston face. The only way to do that is to start at opposite sides and meet in the middle, thereby effectively halving the distance. This only works if both plugs fire at the same time. Hard to put a cost on this aspect, but significantly mis timed plug firing is "wrong" from a design standpoint.

Toobuilder said:

The 75/25 ratio is a sound bet if you are trying to simply do a cost analysis for fuel savings. However, keep in mind that dual plugs are not there for redundancy- they're there to allow the flame front to get all the way across the piston face. The only way to do that is to start at opposite sides and meet in the middle, thereby effectively halving the distance. This only works if both plugs fire at the same time. Hard to put a cost on this aspect, but significantly mis timed plug firing is "wrong" from a design standpoint.

Click to expand...

I had a very noted engine builder tell me the same thing. They felt strangely that both plugs should fire at the same time for the long term health of the engine. They did not like mixing ignition types. On the flip side however there is a huge operational data base of one mag and one EI ignition systems flying with no ill effects.

George

Absolutely. It's a case where the situation may be "wrong" in principle, but nobody has a compelling evidence it does harm in practice.

Toobuilder said:

The 75/25 ratio is a sound bet if you are trying to simply do a cost analysis for fuel savings. However, keep in mind that dual plugs are not there for redundancy- they're there to allow the flame front to get all the way across the piston face. The only way to do that is to start at opposite sides and meet in the middle, thereby effectively halving the distance. This only works if both plugs fire at the same time. Hard to put a cost on this aspect, but significantly mis timed plug firing is "wrong" from a design standpoint.

Click to expand...

This maybe the most compelling reason for me to go to dual PMAG, considering that it is not free or cheap. From most people, including the ignition providers, I have heard that the net effect of two EI vs. . only one is very little.

Just to share my technical info and hoping to see it compares with others who have one PMAG and one MAG

My RPM drop on the ground (1700-1800 RPM) is actually worse with PMAG than Slick (90 RPM drop vs. 70)

In the air with 20? and 2400 RPM, my PMAG does better than Slick (30 RPM drop vs. 40)

Here are the CHT/EGT numbers

On Both
C1 C2 C3 C4 C1 C2 C3 C4
330 335 340 328 1413 1418 1406 1412


Only MAG
C1 C2 C3 C4 C1 C2 C3 C4
295 308 307 303 1541 1505 1523 1499


Only PMAG
C1 C2 C3 C4 C1 C2 C3 C4
313 320 325 314 1474 1512 1467 1499


Clearly the PMAG is doing better than the MAG as you see a rise in CHT and drop in EGT compared to the MAG, but I am wondering if this is as a result of advanced timing or simply a hotter spark or both.

Toobuilder said:

The 75/25 ratio is a sound bet if you are trying to simply do a cost analysis for fuel savings. However, keep in mind that dual plugs are not there for redundancy- they're there to allow the flame front to get all the way across the piston face. The only way to do that is to start at opposite sides and meet in the middle, thereby effectively halving the distance. This only works if both plugs fire at the same time. Hard to put a cost on this aspect, but significantly mis timed plug firing is "wrong" from a design standpoint.

Click to expand...

Mike makes a good point. Most of our cylinders are 5-1/8" in diameter and it does take a while for the flame front to propagate. However, as he stated in his next post, there is little evidence that two mags firing at different times is causing harm.

When asked, I tell people to put in one P-mag and keep their traditional mag. After a year they will install a second P-mag.

N941WR said:

Mike makes a good point. Most of our cylinders are 5-1/8" in diameter and it does take a while for the flame front to propagate. However, as he stated in his next post, there is little evidence that two mags firing at different times is causing harm.

When asked, I tell people to put in one P-mags and keep their traditional mag. After a year they will install a second P-mag.

Click to expand...

Bill,
How true! I ran a Bendix mag and Electroair for over 20 years in 2 different RV/Rockets with no ill effects, 1 GPH fuel savings compared with dual mags and clean, cheap automotive spark plugs.
In over 2500 hours of flying in both my Rocket and RV4 with the EI/Mag combo I only had 2 failures. Both times the EI got me home when the Mag coil was the culprit. I barely noticed the Mag failing inflight.

Currently I am running an Electroair/P-Mag combo in my X, works very well...

V/R
Smokey


https://www.iac.org/files/magazines/Sa-2013-08.pdf
FL 220 in a Pitts! (page 13)

I went from mag/mag to mag/EMag to PMag/EMag to PMag/PMag. First change saved me 1 gph, and gave quicker starting. Second change only saved about .2 gph, but gave me a 4 mph speed increase and smoother operation and lower idle speed. Third change gave a little peace of mind...

Bob