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Originally Posted by DarrenWS6
Ok thanks. I should probably study these things further. I never understood what 'ping' is, is that when WOT and the rev limiter is bouncing off?
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No, "ping" is preignition. The fuel/air mixture is igniting just a tad too soon (before top dead center) and the expansion is happening too fast as the the piston is reaching the top of it's stroke. Basically, the gas is trying to expand just as the piston is doing its best to compress everything. The result is a sound that's like rattling marbles in a can. Once you hear it, you'll never NOT know what it is again.
Since the gas is expanding as the piston is trying to compress the mixture, there are severe stresses on the rods and the cylinder walls (mostly the rods, I think). It also heats things up quite a bit. A lean mixture can bring on ping, even when the timing is exactly according to specs. A "little" bit of ping now and then is no problem. But, heavy ping can destroy your engine. It of course also robs you of power, since the expanding gasses work against the desired movement of the pistons.
- Jack