Timing Advance - Confused
05-24-2005, 08:11 AM
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Timing Advance - Confused Hi Folks
I have been reading some threads about how much timing you should add to car. First, I tried the max timing (~28*) and no Knock sensor indications - appears to work well. But then I read a thread that said that is not the way to go because LS1 don't need that much timing advance. I guess the question I would ask, has anybody done any Dyno testing for different timing setting to see the difference in performance?
Thanks - I appreciate any information.
Bill
I have been reading some threads about how much timing you should add to car. First, I tried the max timing (~28*) and no Knock sensor indications - appears to work well. But then I read a thread that said that is not the way to go because LS1 don't need that much timing advance. I guess the question I would ask, has anybody done any Dyno testing for different timing setting to see the difference in performance?
Thanks - I appreciate any information.
Bill
05-24-2005, 09:14 AM
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As a matter of fact, the dyno is the best place to see what timing adjustments will do to your efficiency. Every car will like it's own value, but generally b/w 25-30 is what LS1s like (For NA anyway).
05-24-2005, 09:43 AM
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There's a torque vs timing curve for every load-point
and it has a peak-torque-output optimum with a
region of flat-top as you approach it, and a cliff to
your right (detonation).
Fueling changes the mixture burn speed and thus
the point at which you want to start the burn, so
that the pressure-pulse is optimally positioned
against crank angle to deliver the greatest torque
impulse to the flywheel. Similarly the cylinder
charge effects of scavenging/filling (heads, cam,
headers), compression ratio, chamber temps
all play into burn speed and peak pressure. This
all drives an individual car's optimum spark-
point.
A high speed burn is what you need for high RPM.
A high speed burn is good for fuel economy and
emissions. A slow speed burn may deliver more torque
impulse total, as pressure*time*cos(crank_angle).
Too slow or too late a burn blows useful energy
out the tailpipe (not to mention more partially-burned
goo)and steals from the next cycle's filling by leaving
more residual pressure.
I have always wanted to get my hands on a
methodically-taken dyno series that varies fuel air
multiplier and spark advance in a matrix of pulls, to
see where the ideal for both (because you can't
separate them, they are synergistic) lies. Even
though my own setup probably differs from anyone
else's in the details, it would be very enlightening
to see how the optima vary by RPM; I've seen a
variety of PE vs RPM strategies and for each the
spark would have to follow.
and it has a peak-torque-output optimum with a
region of flat-top as you approach it, and a cliff to
your right (detonation).
Fueling changes the mixture burn speed and thus
the point at which you want to start the burn, so
that the pressure-pulse is optimally positioned
against crank angle to deliver the greatest torque
impulse to the flywheel. Similarly the cylinder
charge effects of scavenging/filling (heads, cam,
headers), compression ratio, chamber temps
all play into burn speed and peak pressure. This
all drives an individual car's optimum spark-
point.
A high speed burn is what you need for high RPM.
A high speed burn is good for fuel economy and
emissions. A slow speed burn may deliver more torque
impulse total, as pressure*time*cos(crank_angle).
Too slow or too late a burn blows useful energy
out the tailpipe (not to mention more partially-burned
goo)and steals from the next cycle's filling by leaving
more residual pressure.
I have always wanted to get my hands on a
methodically-taken dyno series that varies fuel air
multiplier and spark advance in a matrix of pulls, to
see where the ideal for both (because you can't
separate them, they are synergistic) lies. Even
though my own setup probably differs from anyone
else's in the details, it would be very enlightening
to see how the optima vary by RPM; I've seen a
variety of PE vs RPM strategies and for each the
spark would have to follow.