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  #21  
Old 01-24-2019, 10:29 AM
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Fred.Stucklen Fred.Stucklen is offline
 
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Default PMAG Timing

Quote:
Originally Posted by N941WR View Post
A few comments about P-mag configurations:
1. We have not heard of any Lycomings where the P-mags should be run on the "B curve" (no jumper). The "B Curve" starts firing the ignitions at 30.8 degrees BTC and advances out to 39.2 degrees. My personal belief is this was designed for very low compression engines, such as a small Continental.
So now I'm confused. I have dual PMAGS (Ver 114 with the latest software) on an IO-360 BIA engine. If the "B curve" start timing is 30.8 degrees BTC, what would the "A curve" starting timing be? Is it the same?
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  #22  
Old 01-24-2019, 10:36 AM
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Quote:
Originally Posted by Fred.Stucklen View Post
So now I'm confused. I have dual PMAGS (Ver 114 with the latest software) on an IO-360 BIA engine. If the "B curve" start timing is 30.8 degrees BTC, what would the "A curve" starting timing be? Is it the same?
See post #1 for your answer
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  #23  
Old 01-24-2019, 11:54 AM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Fred.Stucklen View Post
So now I'm confused. I have dual PMAGS (Ver 114 with the latest software) on an IO-360 BIA engine. If the "B curve" start timing is 30.8 degrees BTC, what would the "A curve" starting timing be? Is it the same?
As Ray's post above mentioned, this is covered in my first post.

The "A curve" starts firing at 26.6 degrees BTC and advances out from there as manifold pressure drops off.
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Last edited by N941WR : 01-24-2019 at 01:19 PM.
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  #24  
Old 01-24-2019, 12:17 PM
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N941WR N941WR is offline
 
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Please note that I changed the initial post to clarify that the timing configuration I recommend can be achieved by leaving the jumper in and clocking the P-mags as described on page 13 of the Emag Ignition manual.

You can get to the required timing without purchasing a USB to serial connector, loading software, or buying an EICommander.

Clocking is an acceptable method of complying with your engine manufacture's recommended timing configuration.
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Last edited by N941WR : 01-24-2019 at 01:17 PM.
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  #25  
Old 01-24-2019, 12:46 PM
Scott Hersha Scott Hersha is offline
 
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Yes, I timed the mags at about 1.5* after TDC with the jumper still in, which slides the ‘A’ curve to the right. This means that on start up, the mags will fire 1.5* later than when they were timed at TDC (5.7* vs 4.2 with V40 on 114 mags). This also means the advance shift will fire 1.5* later (25.1 vs 26.6), and the max advance will be 1.5* later also (33.5 vs 35.0). The ‘A’ curve is the same as before, but it is de-tuned a little to be a little less aggressive. The variable timing starts to become more advanced at the same place - about 25” MAP and continues its linear shift until about 22” when it’s at the max advance - about 33.5* in my case now.

This all assumes I’m good at setting my timing mark at 1.5* after TDC. I didn’t have a propeller protractor to do this, so my method of measurement might be a little crude. I did this timing change yesterday and haven’t flown it yet to see what the result is. I don’t have CHT issues, in fact, my engine runs very cool, but my reason for making a change is because of what I’ve read on this site about overly aggressive spark advance, and reports/recommendations from Axel and Bill. I’ll try to get some numbers when I can, and see if I can find a protractor around here to more precisely set my timing.
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  #26  
Old 01-24-2019, 12:58 PM
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N941WR N941WR is offline
 
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Scott,

I wouldn't call it "detuned" but rather "properly tuned".

Our experience and that of our customers indicate that you should see slightly more powered but with cooler CHT's.

Good luck, we are all like looking forward to seeing your numbers.
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  #27  
Old 01-24-2019, 01:01 PM
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Quote:
Originally Posted by Scott Hersha View Post
I’ll try to get some numbers when I can, and see if I can find a protractor around here to more precisely set my timing.
You dont need a protractor. Use the teeth on your fly wheel and some simple math to get better accuracy. Assuming a 149 tooth wheel, 360 degrees divided by 149 teeth = 2.4 degrees per tooth.

erich
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  #28  
Old 01-24-2019, 01:05 PM
Scott Hersha Scott Hersha is offline
 
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Eric,
That’s what I did, but it seems a little crude because I’m dealing with less than a full tooth. I’m probably pretty close though.
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  #29  
Old 01-24-2019, 01:18 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by Scott Hersha View Post
Eric,
That’s what I did, but it seems a little crude because I’m dealing with less than a full tooth. I’m probably pretty close though.
Better to err on the safe side and go "too retarded". Its the initial advance of the Pmag curve that's the spooky part, but fortunately that high power range just happens to be the most insensitive to ignition retard WRT power output. Reference my flight testing at 100% in the Rocket: a timing sweep from 20 to 30 degrees had ZERO effect on power output (IAS), but the temps sure went up at the high advance.

Mechanically spoofing the timing to a retard certainly pulls some off the high end which is likely to hurt your LOP efficiency, but that's a reasonable trade for increased detonation margin IMHO.
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Last edited by Toobuilder : 01-24-2019 at 01:21 PM.
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  #30  
Old 01-26-2019, 04:25 PM
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Fred.Stucklen Fred.Stucklen is offline
 
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Default PMAG Timing

Quote:
Originally Posted by Fred.Stucklen View Post

A few comments about P-mag configurations:
1. We have not heard of any Lycomings where the P-mags should be run on the "B curve" (no jumper). The "B Curve" starts firing the ignitions at 30.8 degrees BTC and advances out to 39.2 degrees.
I've been running the "B curve" timing on my IO-360B engine for the last 1620 Hrs. The only times I've seen high CHT's is when I try to do aggressive full power climbs at gross weight on a hot day (or after taxing for too long, then taking off).

So after I read this tread, I decided to try running the engine with the timing set to the "A curve - jumper in". Note that I'm running the Sensenich metal cruise prop (85 pitch). Here is what I noted as differences:

• The CHT’s definitely ran lower by 25*-30*. Max temps in cruise was under 300* (high 290’s). We did not see any CHT overheating on climb out today (at the same full load point), but the outside temps were only in the mid 50’s, so it probably wouldn’t have happened anyway.

• The EGT’s were definitely higher at about 100* hotter, or around the low 1400* temp point (engine leaned). This is an indication that there is fuel still burning when the exhaust valve opens. I noted that during the slow leaning process, the EGT’s went well over 1500*….

• Fuel burn was higher by about .5 gal/Hr. I was not able to get the same RPM’s at the “B curve” gal/Hr. leaning point. An indication of less power??

• Take off RPM was only 2290 RPM, a bit lower than when the “B curve” timing was used. I interpret this as an indication of less available power.

• The engine did idle at a lower RPM, almost stalling and definitely below the PMAG power output RPM (which then required ship power to keep them running).

So, overall, I’d say that there was a loss of performance for the lower CHT's. Tomorrow I’m going to remove the jumper and take some more numbers… I might also try retarding the timing manually somewhere in between the two PMAG curves.
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