Too little spark plug gap. problems?
Thread Starter
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
Too little spark plug gap. problems?
What are the associated problems with a too little spark plug gap?
When I say "little" I'm speacking of around 0.020" or less!!
I found my spark plugs (not installed by me... I was sure the mechanich checked tha gap ...
) all with .020" gap.
The car was running fine. Even at 5500 rpm . No misses, no problems...but probably the engine was not performing on its best potential.
What I like to understand is if this situation can lead to others problems.
Timing, rate of burnig the air-fuel mixture, pinging tentency ...
Thanks
-Beppe-
P.S I gapped the plugs to .040 and I have back cutted...
Obiouvsly (seat of the pants) it seems to run much better, but all we know how we feel better our car after a modification...
When I say "little" I'm speacking of around 0.020" or less!!
I found my spark plugs (not installed by me... I was sure the mechanich checked tha gap ...
) all with .020" gap. The car was running fine. Even at 5500 rpm . No misses, no problems...but probably the engine was not performing on its best potential.
What I like to understand is if this situation can lead to others problems.
Timing, rate of burnig the air-fuel mixture, pinging tentency ...
Thanks
-Beppe-
P.S I gapped the plugs to .040 and I have back cutted...
Obiouvsly (seat of the pants) it seems to run much better, but all we know how we feel better our car after a modification...
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
A wider gap exposes more A/F mixture to the spark. However a wider gap takes more voltage to fire. As long as the narrow gap is lighting the mixture, there is nothing wrong with it. Wear, tear, and use will cause the metal of the plugs to erode, over time, opening the gap, slightly. The spec on mine, with an HEI is .045". Years back I saw HEI spec'ed as high as .060. Higher compression pressures and higher rpms of a modified engine can "test" the ignition system, to the point where an engine may benefit from a narrower than stock gap. Otherwise, the wider the better until it misfires.
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Race Director
Joined: Oct 2001
Posts: 19,653
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From: Melbourne Florida
Cruise-In IV Veteran
I run very inexpensive Autolite's in my car...I have been gapping them to .030 for over four years now with no problems at all...I will say that my car spends the vast majority of it's time at the drag strip at WOT, though...it idles the tiniest bit rough due to the tight gap but barely rough enough to mention...
Two years ago I went to change the plugs...they looked absolutely new....we checked the gap and they were all still .030...I put in new ones anyway since we had gotten that far..
Two years ago I went to change the plugs...they looked absolutely new....we checked the gap and they were all still .030...I put in new ones anyway since we had gotten that far..
Thread Starter
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
Thanks to all. I made some research, but what I really want to understand is when smaller gaps are too small, and the related problems.
Say at .020" I haven't problems, but this is considered the lowest limit considering the combination of spark advance, rpm, cam timing, heads, displacement, temp in the combustion chamber ... What happens if the gap is .015 or .010?
The A/F mixture will not be burned completely?...Or the A/F mixture don't care about the duration/lenght of the spark accross the electrodes to start the front flame?
There is the possibility that some raw fuel remain unburned?...(and O2 not burned also that can lies to O2 sensor?)
-Beppe-
Say at .020" I haven't problems, but this is considered the lowest limit considering the combination of spark advance, rpm, cam timing, heads, displacement, temp in the combustion chamber ... What happens if the gap is .015 or .010?
The A/F mixture will not be burned completely?...Or the A/F mixture don't care about the duration/lenght of the spark accross the electrodes to start the front flame?
There is the possibility that some raw fuel remain unburned?...(and O2 not burned also that can lies to O2 sensor?)
-Beppe-
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
msd suggests the idea of using compression ratio's (using a 6al) and determining plug gap and testing by opening up the gap in .005 incriments. Using comp. ratio's here is what they state: up to 10:1 .050-.060, 10.5-13.0:1, .040-.050, above 13, .035-.045.
Last edited by mseven; Sep 18, 2007 at 07:34 AM.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by conv90
What happens if the gap is .015 or .010?
The A/F mixture will not be burned completely?...Or the A/F mixture don't care about the duration/lenght of the spark accross the electrodes to start the front flame?
-Beppe-
The A/F mixture will not be burned completely?...Or the A/F mixture don't care about the duration/lenght of the spark accross the electrodes to start the front flame?
-Beppe-
Also, small gaps are more subject to being closed up, shorted, by deposits or other foreign material lodging in the gap.
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