Ping Ping Ping Knock

"BradandBrooks" wrote in news:X8kHe.80332$5V4.53660@pd7tw3no:

Normally, thin air can run higher timing. My guess is that your computer is messing with the timing. You should look for evidence of overheating which can cause preignition.

The reason that you need higher octane fuels when you advance the timing to the max is....

The lower octane fuel burns faster than the higher octane fuels thus when a lower octane fuel is ignited at an earlier time, the fuel being lower octane burns too quick causing an explosion before the piston can even get to the top of the stroke. The explosion you hear is that darned ping and if it continues to do this, eventually you will wear into the wrist pin or the rod bearing or it can just as well put a hole in through the top of the piston.

...Ron

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68' Camaro RS 88' Firebird Formula 00' Mustang GT Vert

That would royally suck. Royally. And how does air temperature affect this? When it's cold, it never pings, when it's hot, it does.

Thanks.

Brad

Jezus. Buy a cheap timing light, disconnect the spout connector, and then set the timing correctly (and then replace the spout connector). And since you have a 5.0 go-fast car, why put regular in it? Does it not make sense that mid-grade would be better anyways? If you insist on being cheap, I would strongly suggest setting the timing via a timing light to get an accurate measurement.

If you adjusted the timing with your calibrated 'ear', you still needed to remove the spount connector first. If you do not know what the spout connector is, I would suggest a Haynes or Chiltons manual. Crappy Tire sells the manuals and the timing light for decent prices.

HTH,

Chris > Guys,

Chris, I know how to set timing. What I want to know is why temperature affects timing. Obviously, it must be the thinner air.... thanks.

Brad

Sorry on the late reply, my ISP is quite suckola.

Density, the colder the air is the more dense it is, the warmer it is the less dense it is. The colder the air, the less area it needs to fill a given amount. Molecules close together means that you can put more in a given space, or more air/fuel in, the less pinging out.

If you really want to learn about how temperatures work in conjunction with air density you can probably find more information by researching Nitrous oxide detonation an your favorite search engine. I'm in no way an expert on the subject, there are people here that know the physics much better than I do.

...Ron

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68' Camaro RS 88' Firebird Formula 00' Mustang GT Vert

It does not burn faster, it ignites earlier. The compression stroke compresses the air/fuel mixture in the cobustion chamber. Lower octane fuel combusts at lower pressure. The trick is to get the compression up as high as possible (power) but not too high before the mixture ignites by itself before the spark plugs ignites it. Higher octane basically delays the ignition longer (by itself).

Higher octane slows down the combustion process giving you a slower, more controlled burn. The advantage is that it helps to prevent pre-ignition, preventing detonation from hot spots in the combustion chamber. (taken from the link below)

Here's one that describes the combustion process even better. A long read though.

...Ron

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68' Camaro RS 88' Firebird Formula 00' Mustang GT Vert