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 How important is Spark plug Gap?
#835476
09/12/07 04:37 AM
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Joined: Aug 2007
Posts: 34
OP
Getting the Wheeling Fever
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Im not sure how important it is im sure it serves a good purpose but when i checked the gap on my plugs they were 025 and i know they are supposed to be 040 so i re-gapped them and didnt notice any difference.
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Re: How important is Spark plug Gap?
[Re: Boostcreepr]
#835477
09/12/07 04:55 AM
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Joined: Dec 2004
Posts: 5,231
Trail Leader
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Basically, The wider the gap, the harder it is to spark across it. The narrower the gap, the faster the plug wears.
?_________ |_|_|\____\___ l-----[O]≡≡≡≡[O] ()_)()_)-----)_) Stay the Trail! 
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Re: How important is Spark plug Gap?
[Re: Boostcreepr]
#835478
09/12/07 05:08 AM
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Joined: Feb 2004
Posts: 10,238
Web Wheeler
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Always check that the spark plug gap is compatible with the engine manufacturers specification. A gap that is too small means that the spark duration will be very quick and the spark will be thin and weak. The consequences of this may be bad starting and high exhaust emission levels. This will result in an increase in fuel consumption. If the gap is set too large, the ignition system will not be able to cope with the demands and a misfire situation will occur. Some wide gap spark plugs have a longer ground electrode to accommodate a wide gap setting. These must be used where specified, as opening up a standard plug to a wider gap setting may result in the electrodes not running parallel to each other. This could result in abnormal and premature electrode wear.
A couple of other tidbits: 1) A gap too wide will leave gray tracing lines lengthwise on the body of the plug. 2) Run a slightly lower gap (.035") on forced induction engines. Here's a chart with pictures of spark plug issues: Reading Plugs Frank
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Re: How important is Spark plug Gap?
[Re: FrankR]
#835479
09/12/07 02:59 PM
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Joined: Jan 2001
Posts: 13,649
Web Wheeler
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The wider the gap, the larger the spark kernel, and the higher the probability that there is a combustible mixture at the location of the spark and that combustion is started. Also, the wider the gap, the more spark voltage is required to jump the gap, so there's a limit - the voltage generating ability of the coil(s).
While playing with the turbo Raider, I kept getting high rpm random misfires. I found a site that suggested that the VERY high cmbustion chamber turbulence in a blown motor was blowing out the spark before it fired the mixture. I reduced the gap from .039 to .032, and the misfire went away. Note Frank's .035 reco above...
The gap has to be wide enough so that the coil voltage builds up high enough to both jump the gap and be hot enough for a very high probability of combustion. Thus a narrow gap is too cool a spark..
Not responsible for advice not taken...
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