Walter,
Would you care to give us more complete information? For any given
combustion event in a piston 4-cycle engine with certain compression ratio, A/F
ratio, fuel octane, # of ignition points,valve count, piston head and
chamber shape there is an optimal timing to deliver appropriate pressure during
the power stroke. If the timing is changed, the pressure
delivery range is changed. Some of the ways to change the
timing of the combustion events would be to change the A/F (lean or rich), the
octane, and uncommanded ignition events (pre ignition, detonation). If the
event is late, the best pressure applied to piston power stroke may be less
effective because there is little work for the piston to do. If the event
is too early, the pressure may work against the purpose of the engine - the
piston may still be on the compression stroke or too early in the power stroke
where the rod angle isn't in a position to smoothly deliver the power to the
crankshaft, both causing more stress on the engine than is desirable.
The fixed timing compromise delivers less than optimal power under
conditions outside the engine design range specified by the
designer. One of the negative ways to change the timing of the
combustion event is to diddle with the mixture so that the engine is operating
20-30F ROP under high power - this can place abnormally high pressure on the
piston/chamber and at the wrong time.
When all the engine parameters are appropriately controlled, including
ignition timing and A/F ratio, the engine can smoothly and
efficiently deliver the power within its design and engineering.
Thanks for keeping us within the bounds of reason.
Scott Krueger
Green efficiency thru the use of appropriate timing. If I could only get my
stock market timing right...........................
.
In a message dated 1/9/2008 8:14:42 A.M. Central Standard Time,
walter@advancedpilot.com writes:
I think what is happening is that the thetaPP is changed less by the loss
of the mag than by the loss of the EI. This had little to do with the
amount of fuel being burned.
BTW, I just looked at the thetaPP data on a set-up where the timing was
changed by as little as 2 degrees, advanced. The thetaPP was advanced to
10dATDC and the peak pressures were above 1100 psi. This is not a good
thing. You guys do as you please, but that's not something I want to do
to my engine. Spark plugs begin to be blasted out of cylinders at
1200psi--by imperical experience.
These are observations of hard data.