3 ms·

This is true, but in practice you are one flaky knock sensor and a lead foot away, because detonation really is only an issue at high power levels. I'd wager mo

by lutorm 11y ago

This is true, but in practice you are one flaky knock sensor and a lead foot away, because detonation really is only an issue at high power levels. I'd wager most people don't really ever go full throttle and if they do, for a few seconds at most, so I suspect the potential for damage is not that great. If you habitually floor it, though, then yes.

jacquesm 11y ago
That's only partially correct. If your engine 'knocks' regularly you're stressing it in a way that is detrimental to the engine's life-span. If you do it whilst under high power then the risk of damage increases, but doing it over a longer period at lower power level is just as damaging (due to the repeated stressing of the engine materials, specifically the piston heads, the cylinder walls, the gasket material and the valves as well as the head). An engine that knocks regularly will die, no matter what the power levels at which it takes place simply because it isn't designed to deal with that stress on a regular basis, engines are designed with some leeway but not so much margin that they could take such abuse and still manage the same life-span they'd achieve with normal use.
- lutorm 11y ago
  You might be right. My thinking was this: peak cylinder pressure basically is proportional to torque, so at lower power levels cylinder pressure is overall lower. Even if the engine knocks, which will cause a spike in cylinder pressure, it starts from a much lower baseline, and there's also much less air/fuel mixture in there. Thus peak cylinder pressure for a knocking engine at low torque may not be much larger than that of a non-knocking engine at full power. But this is just speculation on my part, I don't have quantitative data. It's also possible that it is the sharp pressure spikes that do the damage rather than the overall pressure level, in which case what I'm saying would be less applicable.

by lutorm 11y ago

jacquesm 11y ago

That's only partially correct. If your engine 'knocks' regularly you're stressing it in a way that is detrimental to the engine's life-span. If you do it whilst under high power then the risk of damage increases, but doing it over a longer period at lower power level is just as damaging (due to the repeated stressing of the engine materials, specifically the piston heads, the cylinder walls, the gasket material and the valves as well as the head). An engine that knocks regularly will die, no matter what the power levels at which it takes place simply because it isn't designed to deal with that stress on a regular basis, engines are designed with some leeway but not so much margin that they could take such abuse and still manage the same life-span they'd achieve with normal use.

lutorm 11y ago
You might be right. My thinking was this: peak cylinder pressure basically is proportional to torque, so at lower power levels cylinder pressure is overall lower. Even if the engine knocks, which will cause a spike in cylinder pressure, it starts from a much lower baseline, and there's also much less air/fuel mixture in there. Thus peak cylinder pressure for a knocking engine at low torque may not be much larger than that of a non-knocking engine at full power. But this is just speculation on my part, I don't have quantitative data. It's also possible that it is the sharp pressure spikes that do the damage rather than the overall pressure level, in which case what I'm saying would be less applicable.