Mailing List lml@lancaironline.net Message #45682
From: <Sky2high@aol.com>
Sender: <marv@lancaironline.net>
Subject: Re: [LML] Re: One mag, One electronic ignition
Date: Mon, 07 Jan 2008 15:51:16 -0500
To: <lml@lancaironline.net>
In a message dated 1/7/2008 10:32:35 A.M. Central Standard Time, glcasey@adelphia.net writes:
From data posted by Scott it looks like the curve is linear from 0 advance at 30 inches to 14 degrees at 10 inches regardless of rpm.  It also looks like there is no rpm advance (except for some way to switch from zero advance during cranking to the base advance).  I'd like to see more data to get a more accurate picture.  Say, do a ground runup and check the advance at WOT/max rpm.  Then fly at 5,000 ft or less and measure the advance at 2300, 2500 and 2700 rpm at manifold pressures of 15, 17, 19, 21, 23 and 15 inches.  This would give me a good picture of the curve.  From what I see so far the curve looks logical, but I would prefer to have zero advance at 25 inches and have it limited to something more like 10 degrees.  The advance at 25 inches means that leaning to best power at 25 inches might get one close to the detonation limit.  Having more advance that would be needed at high altitude cruise means that if the MAP sensor failed to a low value the advance could go beyond what could be tolerated by the engine.
Gary, Gary, Gary.......
 
You cannot map the timing curve from the meager data I reported.  It is driven by RPM and MAP.  The dual system is actually safer than a single system since LSE compares the MAP each is seeing and if there is disagreement, the MAP contribution is eliminated and the advance is retarded to more conservative timing based solely on RPM. 
 
Perhaps you should consider the PMAGs as they allow for timing modification.  I have abandoned the idea of messing with the timing since I am pleased with the results I currently have.
 
When evaluating ignition timing please take into account that fixed timing is a compromise.  That compromise works well enough if "well enough" satisfies ones requirements.
 
Scott Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)

Pilot not TSO'd, Certificated score only > 70%.




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