Detonation and Pre-ignition?
04-05-2007, 03:25 PM
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No, they are somewhat different.
Detonation is when the burn rate goes supersonic
rather than a slow controlled burn. You get a
pressure spike that is well above normal (but no
more total power, just an impact rather than a
push). Integral pressure provides your torque.
Peak pressure provides your busted hardware.
Preignition is when the burn starts before spark
is applied. This would be from gross overtemp,
overcompression or "glow plugs" like carbon in
the cylinder. If you pop too early she a don' like.
If you reach high pressures while still on the
compression stroke this is a great way to see
detonation.
Conditions that favor one, favor the other (high
temp, high compression, over-lean mixture for the
temp*pressure. But they describe two different
aspects (burn speed and burn start).
Detonation is when the burn rate goes supersonic
rather than a slow controlled burn. You get a
pressure spike that is well above normal (but no
more total power, just an impact rather than a
push). Integral pressure provides your torque.
Peak pressure provides your busted hardware.
Preignition is when the burn starts before spark
is applied. This would be from gross overtemp,
overcompression or "glow plugs" like carbon in
the cylinder. If you pop too early she a don' like.
If you reach high pressures while still on the
compression stroke this is a great way to see
detonation.
Conditions that favor one, favor the other (high
temp, high compression, over-lean mixture for the
temp*pressure. But they describe two different
aspects (burn speed and burn start).
04-05-2007, 04:55 PM
#6
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Thanx for for the info. Sooo I was thinking that both were pre-ignition then. Now by not being controlled do mean it burns to fast or more than once? I understand that the spike is putting to much force at once on it but is the before or after TDC or both? Just trying to get a visual. And one last thing is running 100 octane worth it or what? I spay once in a blue moon and don't have a tune.
04-05-2007, 05:42 PM
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Yes,they are different.(Preignition) happens before the regular ignition spark from the spark plug occurs.It can be cause by using spark plugs of too high a heat range or (hot spots in the combustion chamber) such as carbon on the valves or your vehicle running lean.Lean mixtures burn slower than rich mixtures which allows engine parts to be exposed to the flame of combustion longer.Finally,preignition can be caused by too low coolant or a fault with your cooling system.Preignition is spark knock but will not cause parts to break like detonation will. 
(Detonation)can occur when an unburned portion of the air fuel mixture explodes after the regular ignition spark from the spark plug occurs.When this happens it can results in broke parts such as a piston.0ne cause of detonation is using fuel of too low an octane for your vehicle.Detonation can also be caused by igntion timing that is too far advanced.EGR valve failure is another cause.Almost all modern vehicles have a detonation(knock)sensor(mounted on the engine block) to send a signal to the computer that detonation is occuring.The computer responds by retarding the ignition timing until the vibration from detonation goes away.It can result in an engine running like it is on its last leg If it keeps pulling the timing back.Hope this helps.......
(Detonation)can occur when an unburned portion of the air fuel mixture explodes after the regular ignition spark from the spark plug occurs.When this happens it can results in broke parts such as a piston.0ne cause of detonation is using fuel of too low an octane for your vehicle.Detonation can also be caused by igntion timing that is too far advanced.EGR valve failure is another cause.Almost all modern vehicles have a detonation(knock)sensor(mounted on the engine block) to send a signal to the computer that detonation is occuring.The computer responds by retarding the ignition timing until the vibration from detonation goes away.It can result in an engine running like it is on its last leg If it keeps pulling the timing back.Hope this helps....... Last edited by lovescamaros28; 04-05-2007 at 05:53 PM.
