Restoring - General discussions that span across many different groups of years and models > Parts

New Autolite AR32 plugs??

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70cj428:

--- Quote ---I have no real ideas as to what a "racing plug" is except most are "colder" than stock plugs.
--- End quote ---

I know this post is a couple months old, but I figured posting might add some light on this.  The heat range of a plug has nothing to do with how hot the spark is, it's how hot the tip of the electrode gets when the engine is running. If the center electrode is too cool, carbon and combustion byproducts can collect on the electrode, and since carbon conducts electricity the plug will misfire in short order. To make the plug "self clean", the plug tip is allowed to get hot enough to burn off the carbon. If the plug tip gets too hot, it will cause detonation (preignition) and possible engine damage. Since a low compression 6 cylinder in a taxicab makes nowhere near the cylinder pressure and heat that a high compression race engine does it needs a plug that's allowed to get much hotter to stay clean. a low compression engine is also less prone to detonation so it can tolerate a much hotter plug. (BF-82's). Low compression V8's got BF-42's and as some insurance against detonation, high compression production engines got BF-32's. Autolite offered BF-22's and BF-12's for high compression racing applications where detonation can cause major damage and plugs are changed frequently.

So......

If you put BF-12's (really cold plugs) in your K code, it will run fine till the plugs foul in fairly short order and the car runs like crap. However, if you put BF-82's (a really hot plug) in your K code, you could have engine damaging detonation under high heat/load conditions.

If you only take your K code out for weekend cruises and live in new England, and run premium gas, BF-42's will work fine. If you live in Arizona and drag race in the summer, a cooler plug is in order. BF-22's and BF-12's will foul in short order in most street cars. For most collector cars BF-42's are fine, and can be a good idea in some cars that don't get driven much. (ever try and change the left rear plugs in a CJ car with smog ? You may welcome the BF-42's better ability to "self clean".)

Here's a post on the 428 forum where I answered a similar question with more detail and posted a few pic's... (see the last post in the thread)

https://www.428cobrajet.org/forum/index.php?topic=24441.msg164934#msg164934

Actually, the whole post is worth reading

Hope this adds some light on the subject....

John

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