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detenation what exactly is it.

Old 12-24-2003, 06:46 PM
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Default detenation what exactly is it.

Everyone hears that detonation is bad but what exactly is it?

a) when the air&fuel in the cylinder combust before TDC
b) when there is too much air in the cylinder causing a violent uncontrolled explosion.
c) combination of both since more air means less capacitance between the anode and cathode of the spark plug which leads to a) and leads also to b)
d) detenation is just the a pinging sound, I have never heard it but I am sure it would sound like a ping.
e) other


if a is the real evil then retarding would be the good, if b is the answer then more fuel would be good, if c is the answer then retarding and fuel is required, if d is the answer then ear plugs are good.


so someone who knows something educate me.
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Old 12-24-2003, 07:28 PM
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Default Re:detenation what exactly is it.

okay i just read that the stock d16 timing is retarded by 16 degress. why is it retarded in the first place? Once the TDC sersor indicates that the cylinder has reached TOP DEAD center why not just fire the ignition instantly to get max power? is it becuase the not all the fuel from each cycle has not fully squirt into the cylinders so you got to wait? That is my suspision, so if you increase ur injector size and upgrade the fuel pump you can decrease the injector pulse width via AFC and fire almost instantly after the TDC and get max power?
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Old 12-24-2003, 08:41 PM
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Default Re:detenation what exactly is it.

a)not really
b)kind of - you hit it closest here
c)you are thinking too hard
d)hmmm. Not sure what you mean
e)yeah. pretty much

the timing isn't retarded STOCK on the d16. It is set at 16deg btdc. This is 0 deg adv/retard. If you set it at 18deg, it would be advanced 2 degrees. Get it? And if you fire your plug at exactly tdc, you will make very little power. Try retarding it all the way and see what happens. By the time the burn caught up to the piston, it'd practically be coming around again and the exhaust valve would be opening. As for the other questions (related to fuel), WHAT!?!?!? You obviously have no comprehension of how timing or fuel injection work. Please search the internet, and search the forums and then you come back asking more questions about this when you've got a basic grasp. Your second post is soooo far off I can't even get my head around your questions. It is hurting my brain. UNLESS, it is because you think the injector is firing AFTER TDC, then I can get where you are coming from, it is just in left field. It fires at 16deg BTDC - BEFORE Top Dead Center

If you retard it 10 deg, it is STILL firing before TDC. Was this your problem?
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Old 12-24-2003, 10:34 PM
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Default Re:detenation what exactly is it.

oops you are right it i misread my hanes manual it says 16 btdc. okay I am very confused here. From what I read TDC is when the piston reaches the very top of it travel? and I correct on this point? If you fire before the TDC then does that mean you are igniting the piston before it reaches the top of its travel which would total screw your engine up?
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Old 12-25-2003, 08:45 AM
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Default Re:detenation what exactly is it.

okay I found out, ignition occurs before the cylinder reaches the top because it take time for the air and fuel mixture to burn. ---- that must must killer harsh on the rods, now I see what all the fuss about timing and exhuast is about. You have to forgive me for being a bit ignorant, most people retard timing and mod their cars without truely knowing the exact principle behind. it so stuff like this is hardly ever tlaked about.

i also assume that the cam opens the cylinder from 16 to zeros degrees and closes it after 0 degrees until the adquate combustion has occured, based on a 16 degree btdc setting.

So for larger displacement engines do they typically have a more advanced timing since their engines are both more stronger and a larger cylinder volume means that it would take longer for the mixture to fully combust?

does sponteneous combustion ever occur before the ignition signal is sent? it that is what is meant by pre-ignition?

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Old 12-25-2003, 08:49 PM
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Default Re:detenation what exactly is it.

the valves are not open when the piston is traveling up after intake and before ignition because this is the compression stroke and you can't compress when you have air getting out. detonation is caused by the air/fuel mixture igniting before the spark, this is bad because it ***** ---- up. the air/fuel pre-ignites because of hot spots in the combustion chamber. A lean air/fuel mixture would cause detonation because the lack of fuel makes the combustion chamber hotter since the fuel is changing phase and taking heat away from it's surroundings.
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Old 12-26-2003, 10:25 AM
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Default Re:detenation what exactly is it.

Originally Posted by kyle
...this is bad because it ***** ---- up. the air/fuel pre-ignites because of hot spots in the combustion chamber. A lean air/fuel mixture would cause detonation because the lack of fuel makes the combustion chamber hotter since the fuel is changing phase and taking heat away from it's surroundings.
To add, the preignition is not an even burn over the cylinder. This means that the ignition point is not dead over the piston's center. Normally, ignition point occurs on the outer edge of the piston. This puts major uncontrolled pressure on the piston's ring lands. 9 times out of 10, ring land failure is due to preignition (detenation) conditions.

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Old 12-26-2003, 01:40 PM
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Default Re:detenation what exactly is it.

Originally Posted by toalan
i also assume that the cam opens the cylinder from 16 to zeros degrees and closes it after 0 degrees until the adquate combustion has occured, based on a 16 degree btdc setting.
no.. Automobile engines are 4-stroke.
1. intake
2. compression
** insert spark here **
3. power
4. exhaust.

at the end of the power stroke (piston at bottom of it's travel), the exhaust valve opens, the up stroke (exhaust stroke now) pushes all the air out the port. when the piston reaches the top of this stroke the intake valve opens and the exhaust valve closes. (usually there is a slight bit of overlap meaning both are open at the same time). so with the intake valve open and the piston at the top the exhaust valve closes and the piston goes back down, sucking in the air/fuel with it. valve closes when the piston reaches bottom of travel (or close to it) and the compression stroke begins. when the piston is near the top the spark plug fires. plug fires BEFORE tdc like said above because it takes time for combustion to occur.
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Old 12-26-2003, 02:39 PM
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Default Re:detenation what exactly is it.

basically what I said, but with more information.
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Old 12-26-2003, 02:43 PM
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Default Re:detenation what exactly is it.

Originally Posted by crx88Si
...plug fires BEFORE tdc like said above because it takes time for combustion to occur.
..this is correct, and to continue on..

The advancement (setting BTDC) of your timing is very important, because you want ignition to occur 7 - 12 degrees ATDC. This is where the greatest amount of power will be able to be applied to the rod to turn the crank. This is why timing is so very precise, and static timing should always be set to stock, and timing changes should be made to the ECU's ignition map.
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