I tried a 38 everywhere setup, kinda bucked at low rpm steady speed. The map in it right now runs really well and is the smoothest driving setup I've had since the car has been on the road. Mike's cam has something to do with that as well.
Ignition curve discussion
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Re: Ignition curve discussion
I tried a 38 everywhere setup, kinda bucked at low rpm steady speed. The map in it right now runs really well and is the smoothest driving setup I've had since the car has been on the road. Mike's cam has something to do with that as well.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens
Re: Ignition curve discussion
I've heard that, but I've also seen smart guys make the case for a curve that gradually increases a few degrees above "max" advance as RPMs climb to counter the effects of slew rate in the module / coil.Schurkey wrote: ↑Sun Jun 21, 2020 1:50 pmMy understanding--from listening to other folks, not from my own independent research--is that there's no need for additional advance after a certain RPM. In fact, high-RPM use may need a few degrees of "high-speed ignition retard" because the in-cylinder turbulence becomes so much greater as the RPM builds. The turbulence speeds combustion.
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Re: Ignition curve discussion
Squish velocity, the main component of combustion turbulence, does increase proportionally to rpm.novadude wrote: ↑Tue Jun 23, 2020 9:16 amI've heard that, but I've also seen smart guys make the case for a curve that gradually increases a few degrees above "max" advance as RPMs climb to counter the effects of slew rate in the module / coil.Schurkey wrote: ↑Sun Jun 21, 2020 1:50 pmMy understanding--from listening to other folks, not from my own independent research--is that there's no need for additional advance after a certain RPM. In fact, high-RPM use may need a few degrees of "high-speed ignition retard" because the in-cylinder turbulence becomes so much greater as the RPM builds. The turbulence speeds combustion.
Ignition delay, the time period from ignition to self-sustaining spark, is a function of time not degrees. Therefore we need more degrees as rpm increases.
The fastest flame speed usually is found at or very near the torque peak; we need slightly less timing.
Higher engine speeds allow less time for fuel evaporation, reducing mixture quality while requiring an increase in spark advance to maintain the same peak pressure angle.
The peak pressure angle will vary with engine speed and will need an adjustment in spark timing to optimize combustion timing.
When you out it all together, the ideal ignition curve becomes complex; somewhat like the Rocky Mountain Range.
Which is why ECU ignition maps provide the construction of complex curves, often different for each cylinder.
Re: Ignition curve discussion
Makes sense. The optimal curve for our kart engines looked like a stock market chart.David Redszus wrote: ↑Wed Jun 24, 2020 10:26 amSquish velocity, the main component of combustion turbulence, does increase proportionally to rpm.novadude wrote: ↑Tue Jun 23, 2020 9:16 amI've heard that, but I've also seen smart guys make the case for a curve that gradually increases a few degrees above "max" advance as RPMs climb to counter the effects of slew rate in the module / coil.Schurkey wrote: ↑Sun Jun 21, 2020 1:50 pm
My understanding--from listening to other folks, not from my own independent research--is that there's no need for additional advance after a certain RPM. In fact, high-RPM use may need a few degrees of "high-speed ignition retard" because the in-cylinder turbulence becomes so much greater as the RPM builds. The turbulence speeds combustion.
Ignition delay, the time period from ignition to self-sustaining spark, is a function of time not degrees. Therefore we need more degrees as rpm increases.
The fastest flame speed usually is found at or very near the torque peak; we need slightly less timing.
Higher engine speeds allow less time for fuel evaporation, reducing mixture quality while requiring an increase in spark advance to maintain the same peak pressure angle.
The peak pressure angle will vary with engine speed and will need an adjustment in spark timing to optimize combustion timing.
When you out it all together, the ideal ignition curve becomes complex; somewhat like the Rocky Mountain Range.
Which is why ECU ignition maps provide the construction of complex curves, often different for each cylinder.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens
Re: Ignition curve discussion
2-strokes retard at high rpm to put more heat into pipe, which changes the speed of sound to make pipe look shorter and stay in tune.
Re: Ignition curve discussion
That is certainly part of the equation. I know each different pipe had a different optimal curve.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens
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Re: Ignition curve discussion
The fun part came when we found that a two stroke at constant throttle and rpm, would increase EGT with time.GRTfast wrote: ↑Wed Jun 24, 2020 1:35 pmThat is certainly part of the equation. I know each different pipe had a different optimal curve.
Now it was time for the really sharp tuners to go have a beer.
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Re: Ignition curve discussion
Well, EGT sensors are thermal sensors, so isn't that always the case?David Redszus wrote: ↑Wed Jun 24, 2020 8:35 pmThe fun part came when we found that a two stroke at constant throttle and rpm, would increase EGT with time.
Now it was time for the really sharp tuners to go have a beer.
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Re: Ignition curve discussion
At speed or on the dyno?hoffman900 wrote: ↑Wed Jun 24, 2020 8:38 pmWell, EGT sensors are thermal sensors, so isn't that always the case?David Redszus wrote: ↑Wed Jun 24, 2020 8:35 pmThe fun part came when we found that a two stroke at constant throttle and rpm, would increase EGT with time.
Now it was time for the really sharp tuners to go have a beer.