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KobaltBlau KobaltBlau is offline
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Join Date: Mar 2004
Location: City of Seattle, WA
Posts: 3,374
I'll try to answer my own question.

knock is mainly a function of pressure, temperature, and mixture at any given point in the cylinder. For performance, you would like to fire the plug such that you have peak cylinder pressure just after TDC to maximize your average combustion pressure during the burn. However, the earlier you fire the plug before TDC, the more the temperature and pressure ramps up before the piston has a chance to go down. This may cause knock.

Also, turbulence in the combustion chamber promotes even mixture, which keeps a lean physical space in the cylinder from knocking (autoigniting before the flame front gets to it).
Old 07-29-2004, 07:55 PM
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