what does different spark plug gaps do?
Thread Starter
Mopar Fanatic
Joined: Oct 2011
Posts: 179
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From: australia
what does different spark plug gaps do?
Hey all
I did a plug change this week and did the usual plug line up and check for differences.
All my plugs were running rich except for 1
One looked to be running lean. I may have dropped it when installing it or nicked it with the top of the piston
or something but the gap has closed on that plug.
As you can see the light grey plug is the one that has the closed gap.
The plugs came pre set at 1.1mm gaps. I have since installed an autolite plug as these plugs were longer than what my motor recomended.
My question is how the gap effect performance? Larger gap does what? and smaller gap does what?
cheers Maca
I did a plug change this week and did the usual plug line up and check for differences.
All my plugs were running rich except for 1
One looked to be running lean. I may have dropped it when installing it or nicked it with the top of the piston
or something but the gap has closed on that plug.As you can see the light grey plug is the one that has the closed gap.
The plugs came pre set at 1.1mm gaps. I have since installed an autolite plug as these plugs were longer than what my motor recomended.
My question is how the gap effect performance? Larger gap does what? and smaller gap does what?
cheers Maca
Admin
Joined: Apr 2008
Posts: 8,173
Likes: 200
From: Goffstown, NH
Just My Opinion
The difference in gap will either allow the plug to fire or not fire depending on the amount of voltage being passed through it. With that being said:
1. On a stock ignition system, most recommend ~.035" gap. This gap is small even to gguarantee a spark on a properly working ignition system while still far enough apart to create a long enough spark to help burn all the air and fuel.
2. If the ignition system is not up to par (worn wires, corrosion in the dizzy, etc.) and is creating a weak spark, then this idle gap will not allow the spark to travel through the plug and will indicate a problem.
3. If you have an aftermarket ignition system that is producing a higher than stock voltage, then the spark that jumps this gap will be stronger and larger allowing even more of the fuel and air to burn.
If you run a smaller gap, the spark will still jump but you won’t get a full burn and that can cause issues. Same thing if the gap is too large. If you pull a plug and notice a smaller gap, shine a light down the plug hole and try to see the top of the piston for any marks. If you see any then either the plug was/is too long or there is something going on with that piston.
With new plugs, you should always be checking the gap before putting them in, especially after dropping one. Also, get rid of those Autolites and get a set of Champion plugs. I’ve never been able to get another plug besides Champion to work right in a Mopar motor.
1. On a stock ignition system, most recommend ~.035" gap. This gap is small even to gguarantee a spark on a properly working ignition system while still far enough apart to create a long enough spark to help burn all the air and fuel.
2. If the ignition system is not up to par (worn wires, corrosion in the dizzy, etc.) and is creating a weak spark, then this idle gap will not allow the spark to travel through the plug and will indicate a problem.
3. If you have an aftermarket ignition system that is producing a higher than stock voltage, then the spark that jumps this gap will be stronger and larger allowing even more of the fuel and air to burn.
If you run a smaller gap, the spark will still jump but you won’t get a full burn and that can cause issues. Same thing if the gap is too large. If you pull a plug and notice a smaller gap, shine a light down the plug hole and try to see the top of the piston for any marks. If you see any then either the plug was/is too long or there is something going on with that piston.
With new plugs, you should always be checking the gap before putting them in, especially after dropping one. Also, get rid of those Autolites and get a set of Champion plugs. I’ve never been able to get another plug besides Champion to work right in a Mopar motor.
Mopar Lover
Joined: Jan 2013
Posts: 1,281
Likes: 145
From: Cobleskill,N.Y.
I agree Mopar products only run good with champion plugs. In fact when you order plugs fron mopar they are champions NOT NGKs as you are showing in your picture, they run good in bikes and snowmobiles
Last edited by pro-tech; Feb 22, 2013 at 06:08 AM.
Mopar Lover
Joined: May 2012
Posts: 1,380
Likes: 103
From: Debary Florida
X 2 on champions they are the best for mopars
i run my gap at .050 my next plug check i may decrease to .045,
the last time i check my plugs they had a light grey coating on them.
We have a local car mechanic here with a am talk show who said that carbon is a sign of some additive that is not burning leaving the soot deposit behind ie/ added by fuel source or octane booster and even fuel system cleaners. Apparently this leads to a loss of performance.
this was talking around the AMS oil 2 cycle outboard marine synthetic oil...which apparently fully burned and left no deposits. "though we always have deposits" it help correct the ethanol issues with fuel used for out board motors
and apparently a lot of furd truck owners were adding it to their fuel to increase there gas mileage, some called in to say they got 3 - 5 mpg more with the stuff.
i know my vehicle runs better on sunoco gas verses citgo but funny how the sunoco fuel has a hint of diesel in the mix.
i wonder if there a way to find out what additives are in different brand fuels? with performance details of the stuff they put in fuel.
has any one here ever try "tipping the can"?
we can get nitro methane for around 10 a gallon thought of using it to increase performance.
Any thought's on this?
i run my gap at .050 my next plug check i may decrease to .045,
the last time i check my plugs they had a light grey coating on them.
We have a local car mechanic here with a am talk show who said that carbon is a sign of some additive that is not burning leaving the soot deposit behind ie/ added by fuel source or octane booster and even fuel system cleaners. Apparently this leads to a loss of performance.
this was talking around the AMS oil 2 cycle outboard marine synthetic oil...which apparently fully burned and left no deposits. "though we always have deposits" it help correct the ethanol issues with fuel used for out board motors
and apparently a lot of furd truck owners were adding it to their fuel to increase there gas mileage, some called in to say they got 3 - 5 mpg more with the stuff.
i know my vehicle runs better on sunoco gas verses citgo but funny how the sunoco fuel has a hint of diesel in the mix.
i wonder if there a way to find out what additives are in different brand fuels? with performance details of the stuff they put in fuel.
has any one here ever try "tipping the can"?
we can get nitro methane for around 10 a gallon thought of using it to increase performance.
Any thought's on this?
Last edited by Gorts 5th; Feb 22, 2013 at 06:43 AM.
Mopar Lover
Joined: Nov 2012
Posts: 1,846
Likes: 140
if you do ANY plug experimenting test a change on only ONE cyl at a time. if you test all cyls you will be changing all plugs at the 7-11. if you use a to wide gap it will not fail at low RPM, you will need to test at hi RPM.
Mopar Fanatic
Joined: Feb 2013
Posts: 356
Likes: 39
plug gap should be 0.35 reguardless. The gap will not increase performance unless your running a high energy ignition.
A good running engine will have an almost clean sparkplug. Basically it will have just small darker golden color the further down the plug you look.
A black plug is burning oil or running too cold a plug.
A pasty white coating on a plug is antifreeze.
A lean plug the electrode will be warped the plug itself will look clean all the way down.
If there is white specks or shiny specs on the plug its already melting a piston.
A good running engine will have an almost clean sparkplug. Basically it will have just small darker golden color the further down the plug you look.
A black plug is burning oil or running too cold a plug.
A pasty white coating on a plug is antifreeze.
A lean plug the electrode will be warped the plug itself will look clean all the way down.
If there is white specks or shiny specs on the plug its already melting a piston.
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