Quote:
Originally Posted by Larry Brumfield
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When climbing a hill the extra load put on the engine generates more heat which causes the flame to burn faster AUTOMATICALLY. If too much of the burn occurs too close or slightly before TDC the chambers get hot fast because the piston is harder to push down (in fact temporarily static for an instant and basically locked until the crankshaft rotates) or it is still coming up to the top. If the temperature is greater than what the octane will stand then here come the pings or knocks. Retarding the timing moves the best part of the burn beyond TDC and the piston is easier to push down so the heat becomes less and the knocks stop.
Simple.
Larry B.
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No doubt excess heat causes knocking, but my understanding is that the main cause of the knock-inducing excess heat when pulling a hill is greater compression heating due to wide open throttle bringing in a larger air/fuel charge and thereby raising the pressure and compression heating in the combustion chamber. That's why knocking will occur in a poorly tuned car as soon as you step on the gas, even at the bottom of the hill and long before the motor has had time to overheat. As the motor warms up from laboring up the hill, a bad situation becomes worse.
Steve