Plug gap

General engine tech -- Drag Racing to Circle Track

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MadBill
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Re: Plug gap

Post by MadBill » Tue Dec 04, 2018 12:48 am

Maybe Kevin J. can conjure up a study or Clint G. confirm, but I suspect that if all firing cycles of an ICE were even 85% of the very best, with misfires and fizzles deleted, we be seeing at least 20% more power.. :-k
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Re: Plug gap

Post by gruntguru » Tue Dec 04, 2018 12:59 am

I think 20% is on the high side.

"Coefficient of Variation of IMEP
• COV of IMEP quantifies variability in indicated
work per cycle by expressing the standard
deviation as a percentage of the mean IMEP:
COV of IMEP = STDEV of IMEP * 100
IMEP
– While opinions vary, a degradation in vehicle
driveability can typically be noticed when the COV of
IMEP exceeds 3% - 5%."


From http://users.sussex.ac.uk/~tafb8/eti/et ... uality.pdf

David Redszus
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Re: Plug gap

Post by David Redszus » Tue Dec 04, 2018 10:16 am

Years ago, Bosch referenced the effects of ignition misfires for various types of engines. Memory is faulty but I
think it was based on number of misfiring cylinders, percentage of the time each cylinder misfires and the number of cylinders in the engine.

Power loss = # of misfiring cylinders x percent of misfires/ number of cylinders

So, if three cylinders misfire 40% of the time in an eight cylinder engine:
Loss % = 3 * .40 / 8 = .15% loss

I'll try to find the Bosch technical paper if I can.

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MadBill
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Re: Plug gap

Post by MadBill » Tue Dec 04, 2018 10:43 am

Wow, a wealth of information, even if much of the math is beyond most of us!

I haven't yet given it the scrutiny it merits and have bookmarked it for further study, but so far I haven't seen a collation that combines each cylinders' contribution (without individual spark and fuel optimization) with each's best IMEP cycles to identify the best possible theoretical power, but per p. 202 for example, with 28° SA the best cylinder is making ~ 10% more HP than the weakest.

I haven't spotted any WOT numbers for COV, but working from the idle data on p. 96, the mean IMEP is 126 kPa while the highest cycles are around 165, a 30% premium. (Keep in mind that in my post I was cherry-picking 'best' cycles, not working from standard deviation and the like.)
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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