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PMag first start

johnfurey

Well Known Member
My Pmags arrived Wednesday right on schedule so I spent the past 3 days making the change from my 200hr Slick Mags. There were no surprises or anything difficult, just plenty of hours getting everything changed and organized. I have an IO-360 M1B and WW 200 prop. My first start wasn't as quick as I had suspected. I am starting on only one mag since that is the way I had the starter wired with the Slick mags and haven't changed that yet and I don't know if that will make much difference. It took several revolutions and then didn't really want to keep going. After it did catch it ran smooth. The next couple of starts were similar. I have heard people say that they have trouble detecting any change during a mag check without looking at the EGT. Mine were smooth and even but at least as pronounced as with the Slick. With my WhirlWind prop 800 rpm is about as low as it wants to run smoothly. I'm curious how this compares to others and any suggestions to look for.
 
Thanks for sharing your experience, I have mine arriving next week (hopefully) and been preparing it for the installation. I have the same engine but Harzell CS prop and going to keep one Slick and only changing the right mag.

Curious which spark plug are you using?
 
John,
Did you keep the aircraft plugs or did you change to auto plugs?
I have a new ECI with dual p-mags and it is tough to do a mag check.
I get no rpm difference. Only a small EGT rise when a mag drops off. Also start on less than one blade if I get the fuel correct.
 
My recent dual P-Mag installation went similar to what you describe. My engine (O360-A4M / Sensenich FP Prop) starts within 2 revolutions and is smooth down to about 800RPM's. I too see about a 25 RPM drop when I do the regular mag check. I have noticed my EGTs are about 150 degrees lower and my CHTs about 50 degrees higher at my normal cruise setting than they were with my old Slick mags.

I only have 6hrs on them but so far I am very pleased. The real acid test will be starting on the 12th of December when we take a 2week trip to the Caribbean.

:cool:
 
P-mags

I have 2 p-mags on my carbed 0-320. Brad advised to start with both p-mags "on" since they go into a "start" mode. Mag check produces no drop in rpm if either mag is grounded. If the mag's 12v power is turned off also, there is a drop in rpm. Cht's are higher during climb than they were with my previous ignition, but level flight is just slightly higher. I use iridium auto plugs(NGK). Startup is usually 2-3 blades and idle is smooth at 800 rpm. P-mags dont' require a lot of fuel for start-up so be stingy. I lean during taxi. I time each mag separately and double check to make sure each mag retained a green light after the timing process is complete. Make sure your vacuumn lines to each mag are not leaking.
 
I have noticed my EGTs are about 150 degrees lower and my CHTs about 50 degrees higher at my normal cruise setting than they were with my old Slick mags.

So the question has to be asked. In terms of engine life, which of those two parameters is a good thing? One, the other or both?

And what does it actually mean?

:cool:
 
Valid questions David. Looking strictly at the higher CHT doesn't sound like a positive but I will let those with more knowledge and actual experience operating EI share their thoughts and how it effects the "big picture" of engine operation.
 
So the question has to be asked. In terms of engine life, which of those two parameters is a good thing? One, the other or both?

And what does it actually mean?

:cool:

I hope it is because more fuel is being burnt in the cylinder (Higher CHT) and less is escaping into the exhaust and being burnt there (Lower EGT).

I get no RPM drop if I cut the main power to the mags during run up but I get an actual Mag drop (25RPMs) when I do the mag check. Is this OK? I am using NGK BR8ES plugs and the "A" curve in my setup.

:cool:
 
I hope it is because more fuel is being burnt in the cylinder (Higher CHT) and less is escaping into the exhaust and being burnt there (Lower EGT).

...

:cool:
That is exactly what is going on.

None of you mentioned if you have the jumper in, forcing them to tha A configuration. That will give you lower CHT's when compared to the B configuration.

Regarding the idle speed, since you are burning the fuel charge more efficiently your idle speed should be the same, if not slightly higher. The good news is that you should be able to lower it by adjusting your carb/fuel servo.
 
Mag drop

I have two airplanes with IO 360's, dual 113 pmags, auto plugs. The RV shows ZERO mag drop on the ground when leaned to max RPM. This airplane has a digital RPM display, but I am familiar with it enough to detect a slight tone change in the engine on one ignition or the other. I do get an EGT rise. The Hiperbipe OTOH, will show a 50 RPM drop on the cable driven tachometer. This confirms what my ear is telling me (EGT rise is unknown - the indicator is not that fine of resolution). I've often wondered why one airplane shows a drop and the other does not. I've even swapped ignitions between airplanes and the behavior stays with the tail number. One thing that is consistent however - both engines picked up a great deal with the addition of the Pmags.
 
one more data point

ECI IO 360, 9:1 pistons, dual PMags, auto plugs BR8ES, WW200RV prop:

Starting: sometimes I get the priming right, sometimes not:rolleyes: When it's right, it fires very quickly, not even 2 blades. That's about 25% of the time and seldom with witnesses:D It also seems to me that when I've been flying it regularly it starts easier and when there have been long gaps between flights it makes me aware of its displeasure.

For mine, there is a big difference in idle between a first start on a cool morning and taxiing in after a flight. At first start, leaned for idle it will idle smoothly at no less than 750. As it warms up it will stay smooth at lower rpm but I still don't think it will go as low smoothly as a heavier prop with the flywheel effect. It will go lower and keep running but it is more uneven. I'll take the slightly higher rpm for smooth idle in exchange for the weight advantage while still getting to have a constant speed prop!

At runup I used to go full rich, then 1800 rpm, prop check, mag check and I would get a drop of 75 to 125 rpm. Then a friend at Livermore suggested that doing the mag with the mixture leaned a bit would result in a lower rpm drop and he was right. I now run up to around 1750, lean it until I get to 1800 or a bit more and I get about a 50 rpm mag drop. I used to have the LASAR system, then the PMags and never had an rpm drop at mag check less than 50. I think the most important aspect of the rpm drop check is the difference between the two mags, not the amount of drop specifically. All that said, when I do the mag check I'm not looking at the rpm so much as EGT's to see that they are all rising with one mag off.

That said, there's a guy at Livermore with 2 slicks and if he gets more than 50 rpm drop he decowls to find out what's wrong:eek:
 
Today I gave all my work a good inspection and also wired the switches so both mags would fire at start up. Like others have said I used much less prime and it started in a blade or two and ran smoothly at 750. I didn't want to wait for the oil temp to get high enough to do a high power mag check so I did it at 1500 where both mags gave me the same 90-100 rpm drop. As a matter of practice I do my on the ground mag checks at 1500 just to test the P leads and do a real mag check airborne at high power so I will see what drop I get then. All the replies and input have been great and seem to indicate that mine is operating as others. :D Looking forward to the snow melting this week and a few test flights.
 
I hope it is because more fuel is being burnt in the cylinder (Higher CHT) and less is escaping into the exhaust and being burnt there (Lower EGT).

That is EXACTLY not what is going on.

This is a popular myth.

When you see the effects of changing spark timing alone, nothing else (same MP,RPM and fuel flow) on a dyno while measuring the torque (thus HP) and the egt, cht and internal cylinder pressure you start to understand exactly what is going on.

The EGT value is driven by expansion of the combustion gases. PV=NRT. Ask yourself why a 7-7.5: CR engine has higher EGT than say an 8.5:1 engine.:cool:

You are not getting what you think you are, and possibly the opposite.

I would endorse the use of the A or least aggressive curve.
 
To be fair, the answers are far too long winded to answer in an internet forum post. This is why we run a 2.5 day course, and in slowly increasing terms from layman to more technical so that pilots from all walks of life will keep up.

Basically when you hold all other parameters constant, and you advance the spark timing, the internal cylinder pressure rises sooner relative to TDC, as a result you have rapidly expanding gases and it peaks in a much smaller volume of space. So the peak pressure is much higher. This is why you get a higher CHT.

As for the lower EGT, as I explained before PV=NRT, you have a higher change in pressure, Delta P, thus out the exhaust pipe the expansion of gases is greater therefore a lower temperature.

Think of releasing gas from a gas bottle to atmosphere. from a higher pressure bottle it will freeze quicker.

Much of the "hangar talk" we get here is no doubt the same as in the USA. So I am not surprised when popular belief is misguided on both sides of the planet. Some folk believe the more advance will give them more power. All it does is give them higher pressures and at a smaller ThetaPP, and when you do the subtraction of the area under the curve, from BTDC and ATDC you can find that the work in Vs work out becomes a lesser result in HP.

A small amount of advance helps with LOP operation, but at optimal LOP settings it does not need much. You will notice some folk experience this when installing one EI, but when they install the second one they see not much if any difference.

Hope that helps.
 
To be fair, the answers are far too long winded to answer in an internet forum post. This is why we run a 2.5 day course, and in slowly increasing terms from layman to more technical so that pilots from all walks of life will keep up.

Basically when you hold all other parameters constant, and you advance the spark timing, the internal cylinder pressure rises sooner relative to TDC, as a result you have rapidly expanding gases and it peaks in a much smaller volume of space. So the peak pressure is much higher. This is why you get a higher CHT.

As for the lower EGT, as I explained before PV=NRT, you have a higher change in pressure, Delta P, thus out the exhaust pipe the expansion of gases is greater therefore a lower temperature.

Think of releasing gas from a gas bottle to atmosphere. from a higher pressure bottle it will freeze quicker.

Much of the "hangar talk" we get here is no doubt the same as in the USA. So I am not surprised when popular belief is misguided on both sides of the planet. Some folk believe the more advance will give them more power. All it does is give them higher pressures and at a smaller ThetaPP, and when you do the subtraction of the area under the curve, from BTDC and ATDC you can find that the work in Vs work out becomes a lesser result in HP.

A small amount of advance helps with LOP operation, but at optimal LOP settings it does not need much. You will notice some folk experience this when installing one EI, but when they install the second one they see not much if any difference.

Hope that helps.

THANKS. It did help a lot in my understanding and it all makes sense.

:cool:
 
Dave, I am in total agreement with your analysis. I have had much recent experience that has taught me a lot about timing and temps (CHT's and oil). I am coming to believe that a large percentage of people who are experiencing high CHT's are probably running too much advance. This leads me to a question -

There certainly is a point where less advance does begin to effect horsepower. Where is it and how do you determine where it is for your engine??

Thanks
 
Dave, I am in total agreement with your analysis. I have had much recent experience that has taught me a lot about timing and temps (CHT's and oil). I am coming to believe that a large percentage of people who are experiencing high CHT's are probably running too much advance. This leads me to a question -

There certainly is a point where less advance does begin to effect horsepower. Where is it and how do you determine where it is for your engine??

Thanks

What do you mean by less advance? The HP produced is a relatively flat curve when +/- 2 degrees of the engine spec. Lets assume 25DBTDC, less than that and LOP ops suffer, more and CHT goes up. At high powers (take off and climb) a couple of degrees is really noticeable.

There is less lag in an EI, so the actual spark timing at the plug is sooner with an EI as well, so just because you set it at the same timing mark, lets say 25 degrees, chances are most EI's will fire the plug before the mag does.
 
You're looking for peak cylinder pressure to occur just after TDC. Since the piston speed is highly variable, but the flame front speed is less so, the start of the ignition event needs to vary to line up with peak ICP at xx degrees ATDC. The diameter of the piston (flame travel distance), RPM, mixture, altitude, port geometry, fuel atomization, inlet temperature, camshaft profile and a host of other variables will determine the "optimal" ignition timing for a particular engine. It's true that we are closer to parity with our similar (and similarly built) aircraft engines than a pair of automotive engines, but "correct" timing does play a role. I don't think it?s appropriate to peanut butter spread the implication that the Lycoming "likes" xx degrees of advance.

If I'm off base, please let me know.
 
Asking the question another way-

I have just recently gone to a 9:1 compression on my IO-360, ported cylinders - Impulse Bendix left, LSE plasma II right. CHT's and oil temps ran high at 25 BTDC and LSE at 0 TDC (static). Reset mag to 20 BTDC and LSE to 5 degrees after TDC static (as recommended by Klaus for the LSE with 9:1 compression).

This dropped temps down to normal -CHT's high 390's, WOT, 2600 RPM in a climb and 185 max oil, leaned to 150 ROP. In flight, engine runs well with fuel flows and performance as expected at appropriate ROP cruise settings (150 - 100 ROP depending on percent power) . When securing the mag in flight at these higher power settings, the engine continues to run fine (no speed decrease) but my CHT's will still drop 20 degrees or so.

That indicates to me that the mag is still more advanced than the LSE at that power setting. Seems I could advance the LSE a few degrees to basically match the advance of the mag (as opposed to further retarding the mag to match the LSE - this would result in "less advance" than optimal).

So I guess my question is, With no engine dyno in flight, how do you know if you have optimized your timing to somewhere near the spot Michael describes??

Seems to me you want as much advance as possible while getting acceptable CHT's (380 or so max for me in ROP cruise) assuming all other parameters are in agreement with the charts.

Sounds obvious but it takes some fiddleing. I guess this is where the ability to read advance in flight (via the P-mag Commander or similar) becomes valuable.
 
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Just some random answers and thoughts in RED

Asking the question another way-

I have just recently gone to a 9:1 compression on my IO-360, ported cylinders - Impulse Bendix left, LSE plasma II right. CHT's and oil temps ran high at 25 BTDC and LSE at 0 TDC (static). Reset mag to 20 BTDC and LSE to 5 degrees after TDC static (as recommended by Klaus for the LSE with 9:1 compression). A really good idea, but the EI is still advanced of a normal magneto

This dropped temps down to normal -CHT's high 390's, WOT, 2600 RPM in a climb and 185 max oil, leaned to 150 ROP. High 390's is not what I would call normal but I bet it is much better. If you are leaned to 150ROP in the climb were you at 7000'/2600RPM at the time? If not you were not rich enough and that is not helping your CHT's. And how did you know it was 150dF ROP, did you find peak and come back again or was it a guess? In flight, engine runs well with fuel flows and performance as expected at appropriate ROP cruise settings (150 - 100 ROP depending on percent power) Hopefully 65-70/75%. When securing the mag in flight at these higher power settings, the engine continues to run fine (no speed decrease) but my CHT's will still drop 20 degrees or so. That is normal of any engine, as the ThetaPP has increased as a result of only one plug firing.

That indicates to me that the mag is still more advanced than the LSE at that power setting.I think that is a wrong assumption Seems I could advance the LSE a few degrees to basically match the advance of the mag (as opposed to further retarding the mag to match the LSE - this would result in "less advance" than optimal). I think you have this around the wrong way. You would need to retard the EI to match the mag if you wanted to do that.

So I guess my question is, With no engine dyno in flight, how do you know if you have optimized your timing to somewhere near the spot Michael describes?? Ahhh Optimised ThetaPP, well you can do it if you have an ignition system that reads the peak pressure and crank angle continuously and makes individual spark plug firing changes to achieve the optimal output. And no this is not available in your cars either. There is such a system that is patented and still under development. I could mention the companies name but some folk here get all excited with me promoting some folk from Ada Ok. You could just click here http://www.gami.com/prism/prism.php

Seems to me you want as much advance as possible while getting acceptable CHT's (380 or so max for me in ROP cruise) assuming all other parameters are in agreement with the charts. CHT is not a good parameter to use as a target, and you do benefit from some advance, but not as much as many think. But when LOP it certainly helps.

Sounds obvious but it takes some fiddleing. I guess this is where the ability to read advance in flight (via the P-mag Commander or similar) becomes valuable. Helps you in some sense but reading the ICP and ThetaPP is where you really want to be. ;) ?.not so easy for most of us.
 
Sounds obvious but it takes some fiddleing. I guess this is where the ability to read advance in flight (via the P-mag Commander or similar) becomes valuable.

You can tap off the LSE and monitor advance with a voltmeter, Klaus sells an optional gauge for this purpose that can monitor RPM, MP, Advance.

Back in my racing days optimal timing was found by advancing the ignition until audible detonation was heard (pinging) then backing it off just enough to stop it. This gave you the maximum advance possible without destroying the engine.
 
...Back in my racing days optimal timing was found by advancing the ignition until audible detonation was heard (pinging) then backing it off just enough to stop it. This gave you the maximum advance possible without destroying the engine.

Right. And in my drag race days, it was the quarter mile times that determined the best timing for that engine/track/air. Plug heat range was determined by selecting the hottest plug possible without detonation (as indicated by reading the plug after a run).

So to David's point, yes, a "smart" ignition is the ultimate... But that doesn't exist quite yet. At the opposite end of the scale is the locked out magneto which is religiously set to the data plate advance, regardless of how far the engine might be from the factory configuration. So I will agree that an arbitrary advance in timing may not help (if some is good, more must be better...), a variable timing scheme as offered by the electronic ignitions available is a good start. That is, if a century of automotive development is an indicator.
 
Thanks guys for the responses. It has spurred more reading, here and in other places and more learning. I can see where my initial conclusions were a result of an overly simplistic analysis of a complex phenomenon.

This is made more complex when you have two different ignitions following two different and intersecting advance curves.

For practical purposes, it would appear that the best we can do for setting timing on these "non-standard" engines is make an educated guess and observe the results (engine parameters and aircraft performance) through an educated eye.

It will never be perfectly optimal, but if you can get it close (+/- 2 degrees to "optimal") no harm will be done and you will be getting decent efficiency.

Some of those words make the engineer in me cringe as I type them.

I'll stick to my original contention - I suspect a lot of people experiencing high temps (assuming reasonably good cooling set-up) are running too much advance.

Back to more reading.
 
I too have enjoyed the discussion on all sides of this issue. For the benefit of those planning to install Pmags soon I wanted to report that my 1st flight went as expected. Clean, quick start. No drop in RPM during mag check at cruise power, just a tone change and EGT rise. On this short flight with a shallow climb to 5000' with OAT at 59 degrees and 75% power the CHT's and EGT's are very close to what I had before the switch. Now that the shakedown flight went well I will begin collecting data to make some comparisons.
 
I don?t mean to highjack this post, been reading it with much interest as I will be installing a P-Mag this weekend but keeping one of my slick mags on the left side in place. So, I was wondering if I should change the timing of the slick any different than the 25 BTDC that is recommended for my engine. Also, another question is how best to time the Slick mags? Do you set the buzzer box for the light to come on right at 25 BTDC as the light stays on for a few degrees? I checked my timing and it the light comes on more like 28 degree but stays on as it passes thru the 25 degree mark.
 
Thanks John, looking forward to your further results

Mehrdad, I have used the buzz box for my Bendix mag. I set right at light on. Checked dynamically with a timing light at idle and this timing matches the static buzz box timing exactly.
 
Has Lightspeed, GAMI, E-Mag, or another vendor published their ignition map values?

Has anyone with an accessory display or control ever used the display to record an ignition map?
 
That is something I have looked for before Dan and not found. I must say that it was a while ago.

As for GAMI, no they do not use a map like the existing EI's. The GAMI system is PRISM, Pressure Reactive Intelligent Spark Management. It uses real time pressure data and adjusts the spark on each cylinder to achieve the optimum ThetaPP.

Everything else is a fixed for all, based on static timing or varied according to MP.

Even once we get the maps it would need a serious few days on the dyno in Ada to see what the results really were. A typical HP reading dyno is not enough to really understand the results.
 
The GAMI system is PRISM, Pressure Reactive Intelligent Spark Management. It uses real time pressure data and adjusts the spark on each cylinder to achieve the optimum ThetaPP.

Wonderful concept. Really.

Even once we get the maps it would need a serious few days on the dyno in Ada to see what the results really were.

To what end?
 
To see what the actual effect of those maps are on ICP, ThetaPP and the HP going out the end of the crank.

Advancing spark timing will at a certain point reduce HP. So too much of a good thing, can be bad!

How else do you propose we know for sure what the result is?

Would be fun?.anyone got a pocket full of cash to spend on it? :)
 
It would be nice to have instant feedback with and automatic control for ignition and mixture. Cars have it, although O2 sensors and Knock sensors are still somewhat peripheral compared to direct cylinder data.
Nonetheless, you can perform that function with a fair degree of reliability with mixture control and an Electronic Ignition system which allows the pilot to control timing. As always, your propeller is your dynamometer. Your airspeed indicator, GPS, Variometer, and Engine Information System provide the performance info you need to set up the engine.
Once you establish the best timing curve and mixture for each operating point, it should be repeatable unless a defect develops. Then the EIS or the seat of your pants should figure that out and you can fix it, returning to optimum operating.
You don't need full FADEC. It could be nice, but there are certain operating conditions that favor the human interface, because as of now, the control computer still can't determine your intent. Although that might be moot with millisecond response time in the control computer.
My RV-8 has Tracy Crook's EC-2 Controller coupled to his EM-3 monitor for semi FADEC with manual mixture bias. It's really a speed density system which can tune to the O2 sensor if selected. Timing is also programmable in flight. A very simple yet powerful tool. It's one of the older fuel injection & ignition control systems that uses automotive electronic fuel injectors.
Boy, has this gone off topic !!
I would be in favor of direct cylinder pressure & temperature / real time data that retains some operator control. perhaps it will evolve beyond mixture and timing, but rather earlier or later pressure peak, or Max pressure vs RPM by controlling propeller pitch during load demand changes?
 
To see what the actual effect of those maps are on ICP, ThetaPP and the HP going out the end of the crank. Advancing spark timing will at a certain point reduce HP. So too much of a good thing, can be bad! How else do you propose we know for sure what the result is?

There's no technical reason why GAMI would want the information, as PRISM is a cycle-by-cycle self-mapping system. That leaves only bad marketing; information gathering in order to point out the supposed errors of others.

Let's hope GAMI doesn't go down that road again.
 
Why would they want to do it???

You asked not them?

What is your point Dan? What road Dan?

Is it data that is a problem? They do not need EI data on all the experimental EI's. you asked the question, why?
 
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LSE

Has Lightspeed, GAMI, E-Mag, or another vendor published their ignition map values?

Has anyone with an accessory display or control ever used the display to record an ignition map?

I am working on it Dan. Have data recording on the timing output and ignition derived MAP along with EFIS derived data (map,da,oat,...etc).

Still checking calibrations but getting some good data.

Should have some interesting compilations in another month or so.
 
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