Re: Ign timing; advance vs retard

[Robert Houk - SMCC Bos Desktop Hardware <rdh@UrQ.East.Sun.COM>]

I asked:

   > I wanna make sure I've got this right. Without delving into the myriads
   > of reasons why (relative angle of crank/con rods; varying values of com-
   > bustion burn rate depending on instantaneous cylinder pressure; etc, and
   > so forth) the ignition timing is a variable, one "advances" the timing
   > by causing it to fire earlier in time, or at a "larger" BTDC value, cor-
   > rect? I.e., 10 deg BTDC is 'advanced' timing relative to 5 deg BTDC?

So far it's 3:

	   Yes, you have it correct.  Another way of looking at it, is to 
   graph piston position with respect to time.  It will look roughly 
   (exactly?) like a sine wave, with the very top being TDC.  Anything that 
   happens before that top is called before top dead center, or BTDC, so an 
   event that happens at a greater number BTDC is more advanced.
---
   Correct. BTDC =3D Before Top Dead Center in degrees so a larger BTDC =
   numeric value means 'sooner' as opposed to 'later' or advanced as =
   opposed to retarded.
---
   Correct.  As spark happens earlier, or more "in advance", timing
   is "advanced".

(plus my vote, for a total of 4) to 1:

   Thats retarded (The timing that is). Advancing it would be a positive 
   change. i.e. 2 deg BTDC is advanced relative to 5 DBTDC

You're outvoted, Bob!

					-RDH