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  #21  
Old 09-11-2017, 07:18 PM
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Dbro172 Dbro172 is offline
 
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Quote:
Originally Posted by Bill Boyd View Post
600 +/- hours on P114L's. No issues except CHT's hotter than with mags; when I pull them this week for the inspection and software upgrade while the plane is down for other maintenance, I'll retard them about 2 degrees and see if this doesn't bring me back below 425*F in extended full power climbs, having addressed everything else that's traditionally looked at.

Wouldn't change a thing otherwise. Very happy customer. Hope to put them on an IO-540 in a couple years.
Something to look into; I see two posts here about high CHTs in the climb with with (because of) the PMAGs. As I understand, in a climb, high power low RPM, the PMAGs are firing at (or near) 25 BTDC, so the temperatures would be no different in this phase of flight than with standard magnetos. Isn't it in cruise, when running higher RPM and lower manifold pressure that the spark adavances further BTDC, and gets hotter?

That has been my experience recently, I watched this on my last flight (Friday) I climbed 120 KIAS to 8500' DA , full power, full Rich, with hottest temp say around 375, as I level off, reduce power and lean for cruise, 65% power I can maintain those temps but bump up to 75% power and the hottest temp creeps up in the 390's - 400. (Was 380's with standard mags) Nothing scientific here, and it could be the leaning but definitely seems the temps rise as the firing advances in cruise.
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  #22  
Old 09-11-2017, 07:23 PM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by Dbro172 View Post
Definitely runs hotter, I used EICAD to retard the advance shift by 2.8 degrees which helped but #4 is still warmer than I'd like at a 75% power cruise so I may knock the shift back a bit more.
Quote:
Originally Posted by Dbro172 View Post
As I understand, in a climb, high power low RPM, the PMAGs are firing at (or near) 25 BTDC, so the temperatures would be no different in this phase of flight than with standard magnetos. Isn't it in cruise, when running higher RPM and lower manifold pressure that the spark adavances further BTDC, and gets hotter?
Check out Nigel's article in Kitplanes. His data suggest that there is no advantage to any more advance than the typical Lycoming 25° while running ROP. More CHT heat with no performance increase were his findings.

I found that the default B curve bottom at high RPM/MP was around 32.2 and 35-36.4 around 25".

The default B curve shift is +4.2°. If you lowered that by 2.8° or set it at +2.8°, you are likely seeing ~29.4° at high RPM/MP and around 32.2-33.6° at 25".

If you set it to -2.8° (starting at 0) then you are likely seeing 25.2° at high RPM/MP and around 32.2° at 25".

My findings on the default B curve:


Don Stiver found these numbers for the default A curve:

1. Line two of the data chart notes should read ",,,finally settle at 28..." not 35 as it is written.
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Last edited by Brantel : 09-11-2017 at 07:32 PM.
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  #23  
Old 09-11-2017, 07:33 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Brantel View Post
Check out Nigel's article in Kitplanes. His data suggest that there is no advantage to any more advance than the typical Lycoming 25° while running ROP. More CHT heat with no performance increase were his findings.
Careful interpreting Nigel's article. He mentioned that he has high compression pistons in his Lycoming.

Since Lycoming recommends 25* BTDC for an 8.5:1 compression engine, with high compression pistons, the best timing should be lower than 25.

The P-mags have two timing "curves" (I prefer to call them "configurations"). The A and B configurations. The A config starts at 26.6* BTDC and the B config starts 4.2 degrees higher.

You do not want to run your Lycoming on the "B" (Jumper out) configuration.

Some testing by myself and a few others indicates that for an 8.5:1 compression engine, it is best to configure the P-mags with a negative 1.4 degree offset and a 1.4 degree reduction in max advance. This will bring the high power, takeoff timing down to 25.2* BTDC.

The P-mags are then timed at TDC, as described in the manual.

This configuration can be accomplished in one of two ways, either by connecting them, one at a time, to the Emag EICAD program or via the EICommander.

My personal experience indicates a slight increase in speed and a ~15* reduction in CHT's.
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Last edited by N941WR : 09-11-2017 at 07:36 PM.
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  #24  
Old 09-11-2017, 07:41 PM
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Dbro172 Dbro172 is offline
 
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Quote:
Originally Posted by Brantel View Post
Check out Nigel's article in Kitplanes. His data suggest that there is no advantage to any more advance than the typical Lycoming 25 while running ROP. More CHT heat with no performance increase were his findings.

I found that the default B curve bottom at high RPM/MP was around 32.2 and 35-36.4 around 25".

The default B curve shift is +4.2. If you lowered that by 2.8 or set it at +2.8, you are likely seeing ~29.4 at high RPM/MP and around 32.2-33.6 at 25".

If you set it to -2.8 (starting at 0) then you are likely seeing 25.2 at high RPM/MP and around 32.2 at 25".

My findings on the default B curve:
http://i39.tinypic.com/2ibhi1c.png

Don Stiver found these numbers for the default A curve:
http://i39.tinypic.com/30ix852.jpg
1. Line two of the data chart notes should read ",,,finally settle at 28..." not 35 as it is written.
Yes, good point. I did go -2.8 from "0" (which actually shows up as -12 something when you re-connect to EICAD due to some glitch in the software...) That was a great article from Nigel but I was bummed at the conclusion of essentially no advantage unless running LOP.
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RV-9A #92103 - N803DK (now N9396S)
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  #25  
Old 09-11-2017, 07:43 PM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by N941WR View Post
The A config starts at 26.6* BTDC and the B config starts 4.2 degrees higher.
Don Stiver found using the EI Commander that the bottom of the default A curve was 28° in normal RPM ranges used in flight.

I found using EICAD and my DIY display that the bottom of the default B curve was 32.2° in normal RPM ranges used in flight.

Both curves bring in the advance rather quickly between 24-26".
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Brantel (Brian Chesteen),
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
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Last edited by Brantel : 09-11-2017 at 07:48 PM.
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  #26  
Old 09-11-2017, 07:47 PM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by Dbro172 View Post
Yes, good point. I did go -2.8 from "0" (which actually shows up as -12 something when you re-connect to EICAD due to some glitch in the software...) That was a great article from Nigel but I was bummed at the conclusion of essentially no advantage unless running LOP.
Yes that glitch is there for everyone and it will concern you because it actually shows that much positive shift! It is not real however and the number stored in the Pmag is the correct number.

The no-advantage part is why I have my Pmags limited to 25.2° since I rarely run LOP due to my induction system variability. No more ignition advance induced CHT heat for me! Still worth it for the easy starts, smooth idle and running, car plug advantages.
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Brantel (Brian Chesteen),
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook

Last edited by Brantel : 09-11-2017 at 07:51 PM.
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  #27  
Old 09-11-2017, 07:58 PM
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Dbro172 Dbro172 is offline
 
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So correct me if I'm wrong; if I set the advance shift of the A configuration to -2.8 (from zero) doesn't that limit the max advance to 32.2 regardless of whether or not I changed the "max advance"? (I think I set max advance to 35 but figured its limiting factor was my change to the "advance shift")
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Derek Hoeschen
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RV-9A #92103 - N803DK (now N9396S)
G3X, Superior XO-320, Dual Pmags, Whirlwind GA
www.mykitlog.com/dbro172/

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1968 Mooney M20C - Sold
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  #28  
Old 09-11-2017, 08:03 PM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by Dbro172 View Post
So correct me if I'm wrong; if I set the advance shift of the A configuration to -2.8 (from zero) doesn't that limit the max advance to 32.2 regardless of whether or not I changed the "max advance"? (I think I set max advance to 35 but figured its limiting factor was my change to the "advance shift")
I found the top of the default B curve to be 40.6° so if you subtract the 4.2° (the default B curve shift) from that you get 36.4° and then subtract your 2.8° from that you get 33.6°. So I would say yes, your negative shift value is limiting the max advance to around 33.6°. Also be aware that you have to set your max advance limit to whatever you want -1.4°. This is another quirk in the P-mag. Example: If you set it to 25.2°, in reality the limit will be 26.6° so set it to 23.8° to limit it to 25.2°.

The reason for some of the confusion is the quirks in the Pmag and the Pmag documentation.

I would still set the max advance to what you want it to be (knowing it will be 1.4° more than what you enter) just to be sure it never goes above what you want (think MP sensor failure or something like that).
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RV-7/TU, #72823, N159SB
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Last edited by Brantel : 09-11-2017 at 08:18 PM.
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  #29  
Old 09-11-2017, 08:58 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Dbro172 View Post
So correct me if I'm wrong; if I set the advance shift of the A configuration to -2.8 (from zero) doesn't that limit the max advance to 32.2 regardless of whether or not I changed the "max advance"? (I think I set max advance to 35 but figured its limiting factor was my change to the "advance shift")

The MAP doesn't do anything until above 1800 RPM, regardless of the configuration, IIRC.

When you go to full power, down low, for takeoff, the A config will set the timing at 26.6*. (The B config doesn't really come in to play as no one with a Lycoming should be running it.)

When MAP drops off, the A config will go out to 32.2.

One of the problems, and I talked to Brad about this the other week, is they are not sure if the P-mag is actually advancing 1.4* past the max advance setting or if it is just reporting that it is advancing 1.4* past the max advance.

The P-mag has basically two settings, Advance Shift, and Max Advance.

The Max Advance is exactly that, the maximum limit to allow the P-mags to advance.

The Advance Shift is the degree shift from zero. If you set the P-mags at TDC, then the Advance Shift is 26.6 degrees.

Say you have an angle valve engine and want to have the P-mags work like a fixed timed mag. You can set the Max Advance to 19.6 and leave the Advance Shift at zero. It is my understanding that the P-mags will only advance to 19.6*. However, when I consult with customers, I recommend they enter a negative number in multiples of 1.4 to move the Advance Shift down to match the Max Advance, just in case there is an issue. There may not be an issue but it doesn't hurt to be cautious.
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  #30  
Old 09-12-2017, 11:02 AM
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Two notes...

The OP asked about reliability. Let's hope the users are checking internal power generation at every runup. A 114 series normally transitions to internal power by some mid-teens RPM, but there is no inflight indication if it doesn't; it just runs on external power. Not much reason to run P-mags if the generators don't work, and I have found one failed. BTW, runup checks mean panel switches to kill main bus power to each P-mag, not breakers.

Hopefully EI Commander will soon introduce a one-switch feature so users can select an optimum ignition table for ROP climb (meaning zero advance from the usual fixed timing), then transition to a MP-advanced ignition table for LOP cruise. Full rich while advancing the timing with altitude (the current standard) is dumb as dirt compared to fixed timing and progressive leaning to maintain best power.
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Last edited by DanH : 09-17-2017 at 06:01 AM.
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