Pmag A/B switch

[JohnInReno]

I hope the Pmag and LOP gurus can respond to this. There was a post on this thread:

http://www.vansairforce.com/communit...d.php?t=144919

that implies more ignition advance at LOP on the SDS system.

Like others, I installed the jumper for the less aggressive "A" curve when I began phase 1. It ran so well that I never tried removing the jumper. During a panel mod, I mounted a switch on the panel in place of the "B" jumper. When I switched to the "B" mode, I was delighted with the high altitude LOP operation.

Does it make sense to run the "A" curve ROP during low altitude and climb and then switch to "B" and LOP at altitude?

[DanH]

Originally Posted by JohnInReno

Does it make sense to run the "A" curve ROP during low altitude and climb and then switch to "B" and LOP at altitude?

It could. Do you know the actual timing values?

[DaleB]

From the documentation:

The ignition looks at the jumper state at power-up only. You cannot route these jumper terminals to a switch and go back and forth between curves while the engine is running.

Edit: I'm neither a Pmag guru nor an LOP guru, but I remembered seeing that in the Pmag docs. And EICAD can change it on the fly.

[N941WR]

An A / B switch will not work with the P-mags. At power up, when they aren't spinning, the P-mags read the setting and set the timing appropriately.

Check the manual, page 13, for details.

Take a close look at B configuration, it is not something that should be used on your engine, unless you have lowered your compression.

The A configuration starts at 26.2* BTC, which is still a bit high for a 25 degree engine such as an (I)O-320 or (I)O-360 parallel valve engine with 8.5:1 compression. At lower MAP levels, the A curve will let the timing advance out to about 34 degrees, which is pretty good.

You can modify the B configuration with the EICAD program, free from E-mag, but you can't do it in flight and you will have to do one ignition, then the other.

To change your P-mags in flight, it takes one of our EICommanders.

Feel free call me, if you want to discuss this in more depth. Check your PM's for the number.

[JohnInReno]

Thanks for all the responses. I resorted to reading the manuals and, as pointed out, the A/B jumper is read on power up. I think I will keep the toggle switch in place for now and decide which to use before powering up.

The Base Table in the manual states, "does not represent actual command points". My interpretation is that RPM is shown in the table but the actual table also uses MAP to determine the shift.

Anybody know where to get the actual table?

[Brantel]

This will get you pretty close to the unmodified "B" curve:



The source of this data is logging what the PMag spits out of its serial port while in flight running a series of test runs. This data matches what is displayed with EmagAir's EICAD software when the same test are completed.

Much on this subject in this thread.
As well as some controversy.

You can do your own interpretation of the data and make up your own mind about how to use it but I can tell you this, I am now running the equivalent of the "A" curve with the advance limit set to a value that I feel is safe and I don't have a high compression engine....

[DanH]

Originally Posted by Brantel

This will get you pretty close:

That the B curve?

[Brantel]

Originally Posted by DanH

That the B curve?

Yes, unmodified "B" curve. Added that note to the OP.