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John at Skyport wrote:
Short answer; to get an even mag drop.
Longer answer: the Left mag
fires the Lower plugs which are
closer to the exhaust ports where the mixture is Leaner. Leaner mixture burns slower so it has to be
ignited earlier, i.e. more before TDC.
Why, you may say, don't more engine types use staggered timing? Most
engines fire the lower plugs on one bank and the upper plugs on the other bank
from each mag, so there is no imbalance between the mags, so the mag drop is
even.
Percy notes:
Thus, the Leaner mixture, which could benefit from the Longer time to
burn, gets short-changed. And you pay the Larger fuel bill!
This is an example of "all airplanes are a compromise."
Thankee, John!
Percy
At 12:06 PM 2/28/2005, you wrote:
Do any of you know what the reason is that the timing on a C-75- or C-85-12 is set
RIGHT MAG --28 DEGREES BEFORE TOP DEAD CENTER, AND the LEFT MAG -- 30 DEGREES BEFORE TOP DEAD CENTER ? ??
Short answer; to get an even mag drop.
Longer answer: the Left mag fires the Lower plugs which are closer to the exhaust ports where the mixture is Leaner. Leaner mixture burns slower so it has to be ignited earlier, i.e. more before TDC.
Why, you may say, don't more engine types use staggered timing? Most engines fire the lower plugs on one bank and the upper plugs on the other bank from each mag, so there is no imbalance between the mags, so the mag drop is even.
John Cooper
Skyport Services
PO Box 249
4996 Delaware Tnpk
Rensselaerville, NY 12147
518 797-3064============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers-tech/============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers-tech/
