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Discussion Starter · #1 ·
Newbie question...

If detonation has occured in your engine, that means your spark plug's strap (electrode) got hot enough to ignite the fuel mixture. Could that effect things like spark gap or overall plug health? I haven't pulled the plugs to look at them, but I am noticing what seems to be poor ignition. I bought the car used so I don't know how old the plugs are. Should I pursue this further or am I barking up the wrong tree?
 

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I don't think you guys know what detonation versus knock/ping and pre-ignition really is!

see the second cylinder up from the bottom? munched carnage from DEToNATIoN.



read these first please:

http://www.vtec.net/articles/view-article?article_id=3269

http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp5.asp

it can cause piston meltdown, piston pins cracking, valves flying and breaking off, holes in blocks, etc...it's not fun stuff ....


if you are detonating, then we would be talking about how to rebuild your engines, not just about plugs.

the air fuel mix ignites on it's own without the need of a spark from the plug. If this happens at the wrong time while the piston is going up, instead of travelling on its way down, it can suddenly stop a piston in it's tracks...the piston is slapped down all of the sudden and things break from this tremendous force.
 

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Discussion Starter · #3 ·
You would be right, I don't understand the difference. I thought at least pre-ignition and detonation were the same. ping, I don't know what I thought that was.

I ask this with great reservation. I am sure you have written an article on it somewhere; but I searched and did not find much so I figure it is okay. What is the difference? You are on many other websites that I am not familiar with so if there is an article else where that you could point me to I would appreciate it.

Also, how much damage on that engine was due to previous detonation, as opposed to going into second gear at 90mph. Or was serious detonation the result of the very much botched shift. It seems to me that once you go into second at 90 mph, detonation is at the bottom of your list of worries. I don't know enough to infer which caused what damage.

Woody
 

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the plug CAN be a hot spot source to trigger detonation but more commonly there are sharp edges (particularly when new pistons are installed and aren't sanded down to have smooth edges) or a very hot spark, or high CR in a poorly designed or large combustion chamber, or lean air:fuel ratio, or too much advance all can cause pre-ignition leading to detonation .

poor tuning and sharp edged pistons are the most common causes.

it's a good idea to gap your plugs properly and use the right heat range for your plugs to allow them to dissipate heat. In my 12:1 CR engine I use NGK #7 heat range platinum plugs whose longer electrode wicks away heat faster and the smaller gap has less chance of misfiring. I suggest 0.044 in. for stock CR all motor and 0.040 in. for high CR all motor in terms of gapping.

I don't recommend octane boost since it does have impurities which sticks to the valves and seals and then become ironically a source for hot spots through carbon build up later on. The impurities in octane boost are hard to remove from the valves as my engine builder told me the last time we lapped the valves.


it would be a good idea to get a new set of plugs and go to a #6 heat range platinum if you have stock CR all motor or #7 if you have high CR all motor.

no, I have not written an article on this. I'm glad you asked the question. Many people mix up pre-ignition and detonation. The bad one is detonation. The other one can lead to it.
 

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Discussion Starter · #5 ·
Thanks for the reply. I hate to keep hounding you but, what is the difference? I understand as you said that detonation is worse, and get the general idea of what happens. But, what is the distinction between detonation and pre-ignition.

Thanks again for you patience.

Woody
 

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ever seen an old car keep on running after its shut of? Caused by auto-ignition. Just to kind of give you a picture of whats happening and why its bad ;-p.
 

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diesels do this all the time...

you need a fuel shut off switch to make them stop.

Remarkably the future low emissions gasoline (not diesel) 4-6 stroke engines are trying to create pre-ignition but instead they are trying to control it (dictate when it will happen) to help burn off NOx emissions (the hardest of the 3 to clean up , hydrocarbons and CO being the other 2) and use the auto-ignition to kick the non-combusting piston pair.
 
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