[Uncle]

I know only some of the signs that we can read from spark plugs. Can you determine from "reading" the plugs whether the plugs are too hot or cold or just right? If so, what am I looking for?
Thanks!

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Phil
"I don't believe I'da told that"

[snake]

The tip and ceramic insulater should be clean and a light tan colour.Also at the end of the threads look for a blueish ring all around the plug this means its the right plug heat range that is.

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Don Pell 66 396 Beaumont.
Once bitten twice shy.
Don Pell 66 396Beaumont.
Once bitten twice shy

[Uncle]

Thanks, snake. what does too hot a range look like? What does too cold look like?

[snake]

T.o hot and the plug insulater will blister and cause dention too cold and it will be rich looking.Also too hot and the plug will look white.Hope this helps.

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Don Pell 66 396 Beaumont.
Once bitten twice shy.
Don Pell 66 396Beaumont.
Once bitten twice shy

[Fine69]

Check this out... www.autoweb.lycos.com/garage/encyclop/ency04e.htm

Years ago I remember wanting to see the plugs more of a chocolate brown rather than a light tan. (much like stated in the link above) With our older carb'd cars, is a slight rich condition still perfered or should we be tuning them to get the leaner tan color of computer cars of modern times?

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...Dennis
Topless '69

Looking at the ceramic color is not a true indication of how rich or lean the engine is running. Some fuels have ingredients which will color a plug differently compared to a different fuel.

The ground strap is a good indication of how much heat the plug is seeing. There will be a change of color of the ground strap and this should occur at about the bend of the strap (timing affects this point as well). The threads will show signs of heat and it is usually accepted that you want to see one or two threads heat colored. One other area to look at is tougher to see...there will be a "fire ring" that will form around the porcelin at the base of the ceramic tip, way inside the plug.

This is assuming your tuning at the track for max performance. For street tuning, you simply need to make sure you aren't baking the porcelin, or running way too rich and have a sooty looking plug. I would guess that most street engines are tuned to be on the slightly rich side.

For in depth info on plug reading, Patrick James @ Pro-Systems has a very good advanced tuning video available.

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Malibu Muscle Racing
79 Malibu
414 ci BBC (4.280" x 3.600")
11.13 @ 121.8 mph, 1.56 60'
3650 lbs.

[This message has been edited by Todd Geisler (edited 05-12-2001).]