Ignition advance.... (Chart inside!)
Ignition advance.... (Chart inside!) Hey guys I figured I would throw a teaser out to anybody that will answer. Given a Stock file:
So who wants to guess/enlighten me as to the reason GM put that large dip in the advance curve at 4800 rpm? BTW the colored curves represent different "engine loads". My current idea is that Engine load is approximately the inverse of MAP(rough estimate). Therefore the lower curves on the graph represent WOT.
So, food for thought?
Ryan
So who wants to guess/enlighten me as to the reason GM put that large dip in the advance curve at 4800 rpm? BTW the colored curves represent different "engine loads". My current idea is that Engine load is approximately the inverse of MAP(rough estimate). Therefore the lower curves on the graph represent WOT.
So, food for thought?
Ryan
Re: Ignition advance.... (Chart inside!) Well when My WOT curves looked like this:
Torque peaked right around 4800, I am getting what you are saying BTW.
Its just that I don't have any Dyno time with a stock timing curve. <img src="gr_sad.gif" border="0">
Ryan
[ February 09, 2002: Message edited by: Ryan Karasek ]</p>
Torque peaked right around 4800, I am getting what you are saying BTW.
Its just that I don't have any Dyno time with a stock timing curve. <img src="gr_sad.gif" border="0">
Ryan
[ February 09, 2002: Message edited by: Ryan Karasek ]</p>
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Re: Ignition advance.... (Chart inside!) Well I don't claim to "know" but I'm willing to take a shot at it:
Volumetric Efficiency vs. Torque
Peak torque and VE occur at the same point. Max VE represents the highest cylinder pressure. Higher pressures will detonate sooner (due to faster flame propagation) and mandates less timing advance to prevent knock.
While you'd think the advance would be scaled as a bowl shape, due to cylinder pressures (&VE) as discussed above, it isn't beyond a select area near peak TQ. Why not?
The piston speed at lower RPM's is slow enough that the speed of the flame front requires ignition to be closer to TDC than at higher RPMS (when the time from ignition to TDC is less for the same spark advance setting).
So there it is... cylinder pressures and piston speed. <img src="gr_stretch.gif" border="0">
Volumetric Efficiency vs. Torque
Peak torque and VE occur at the same point. Max VE represents the highest cylinder pressure. Higher pressures will detonate sooner (due to faster flame propagation) and mandates less timing advance to prevent knock.
While you'd think the advance would be scaled as a bowl shape, due to cylinder pressures (&VE) as discussed above, it isn't beyond a select area near peak TQ. Why not?
The piston speed at lower RPM's is slow enough that the speed of the flame front requires ignition to be closer to TDC than at higher RPMS (when the time from ignition to TDC is less for the same spark advance setting).
So there it is... cylinder pressures and piston speed. <img src="gr_stretch.gif" border="0">
