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  #11  
Old 08-17-2019, 06:37 AM
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N941WR N941WR is offline
 
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Do a search on timing P-mags.

You want to either clock them or if you time them to TDC, you need to change the configuration so they fire at 20 degrees BTC and set the max advance to around 25.2 degrees. (Less max advance for the IO-390 than what you see on a parallel valve engine seems to work really well.)

Feel free to contact me with any questions you may have.
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  #12  
Old 08-17-2019, 02:49 PM
JDA_BTR JDA_BTR is offline
 
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Hi Bill, I think your earlier advice was to set max advance to 29.4; why the change to 25.2?

I think it might be good for my unscientific reasons: the system seem so to hunt a bit in the 26-28 setting range and I think I can feel when the ignition changes from one setting to the other..... Maybe I'm imagining it. I'm using the EngineBridge to see what it is doing.
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  #13  
Old 08-17-2019, 03:41 PM
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Quote:
Originally Posted by JDA_BTR View Post
Hi Bill, I think your earlier advice was to set max advance to 29.4; why the change to 25.2?
Can't speak for Bill, but I will back him here. Base 20, advancing to 25 with decreasing MP appears to be right within a mixture range of best power to around 25 LOP. I have dual maps, but mostly just run 23 fixed. Cruising at peak to 25 LOP, 29 BTDC is slower for me, with higher CHT. A trusted source finds 29 offers a small advantage when leaner, i.e. 50 LOP or further.

POSTSCRIPT: 29 BTDC with mixture at 55~65F LOP was good for about 3 knots, as compared to 23 BTDC. Note the mixture dependency...as noted previously, 29 at peak EGT offers a poor result.

Quote:
the system seem so to hunt a bit in the 26-28 setting range and I think I can feel when the ignition changes from one setting to the other..... Maybe I'm imagining it. I'm using the EngineBridge to see what it is doing.
I suspect you're feeling the Power of Suggestion
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Last edited by DanH : 08-23-2019 at 01:45 PM.
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  #14  
Old 08-17-2019, 03:46 PM
JDA_BTR JDA_BTR is offline
 
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I flew today at 10500 DA varying my advance and I thought I had better speed, lower CHT (just a bit) with around 25 too. Then I read this.... good timing. (har har).

Some advice to the unwary: don't change both PMAG at once. One at a time and the engine doesn't care.......
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Last edited by JDA_BTR : 08-17-2019 at 03:50 PM.
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  #15  
Old 08-18-2019, 08:27 AM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by DanH View Post
Can't speak for Bill, but I will back him here. Base 20, advancing to 25 with decreasing MP appears to be right within a mixture range of best power to around 25 LOP. I have dual maps, but mostly just run 23 fixed. Cruising at peak to 25 LOP, 29 BTDC is slower for me, with higher CHT. A trusted source finds 29 offers a small advantage when leaner, i.e. 50 LOP or further....
Dan,

That is exactly why I have changed my recommendation for the angle valve engines.
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  #16  
Old 08-18-2019, 01:49 PM
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Almost there!

P-Mag install going well. Alabama heat on a sunny day in an aluminum hangar not so much, I've had to stop before 11a both days this weekend.

A couple questions:

1) I have noticed a lot of pics of folks grounding their P-Mag Pin #1 to the mag's own installation stud. If I'm reading this right, the manual says not to do that as it's "not a reliable ground" because the retaining hardware is anodized aluminum. That was my original plan to ground, seemed clean and convenient. If the mag installation studs are off limits, on the IO-390, where are you guys grounding?

2) The RPM signal from Pin #6 to the G3X Touch .. had the hall sensor before, if I'm understanding all I really need to do is connect the actual G3X Touch RPM wire (from the 3-wire hall sensor connect) and I'm done, no additional ground needed.

Thanks for any help!
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Last edited by bkervaski : 08-18-2019 at 01:53 PM.
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  #17  
Old 08-18-2019, 02:02 PM
JDA_BTR JDA_BTR is offline
 
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I grounded to case bolts. On the right I went low and on the left I went high. Just backed out the 1/4 nut, put the ring terminal under a new star washer, and that did it. I don't think it matters which case bolts you pick. I wouldn't try to run wire to ground them both at the same place.

I don't know why exactly not to do it at the PMAG bolt, but perhaps uneven clamping forces can occur at the PMAG face that way? Or the ring terminal in the bolt stack there permits a change in torque over time? Either way, it was easy to pick another spot and do it.

As for the Tach, I don't remember about how to wire the RPM from a hall sensor, but I connected my pin 6 directly to the GEA24 J243 Pin 8 according to my records. I only connected one side.

Interestingly, my panel will show 2400RPM when the EngineBridge says the RPM is about 2430. I don't know why the difference. I don't know that there is a way to reconcile that with a setting somewhere even if I did put a tachometer on.
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  #18  
Old 08-18-2019, 02:15 PM
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One caution when connecting the rpm wire to the p-mag: The wire is a shielded wire (at least it is in my Steinair harness), and you need to remove both the shielding and the insulation from the tiny inside wire before making the connection at the p-mag. Otherwise, it won’t work. Ask me how I know.
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  #19  
Old 08-18-2019, 02:25 PM
JDA_BTR JDA_BTR is offline
 
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Yes, I ran a shielded wire as well, grounded only on the Garmin side of the cable; the inner wire is the connection to the PMAG.

I wondered if I could connect the other PMAG to the other RPM connector on the GEA24 and decided not to since the system would probably show it like it was a second engine and not as a redundancy.
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  #20  
Old 08-19-2019, 10:49 AM
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bkervaski bkervaski is offline
 
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Quote:
I wondered if I could connect the other PMAG to the other RPM connector on the GEA24 and decided not to since the system would probably show it like it was a second engine and not as a redundancy.
You can! Pin #8 (I think .. from memory) is RPM2, if single engine it will show the highest of the two, i.e., if one fails you still get a reading.
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