Spark plug question
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Road Master
Joined: Dec 2009
Posts: 1,118
Likes: 5
From: Coweta, Oklahoma
Spark plug question
Do any of you guys know the difference between the 6r10 and the 6r12 plugs? I bought the motorcycle new in Florida but was wondering if that was the preferred plug there and not some places north.
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,210
Likes: 11,335
From: San Diego, CA
Short answer:
6R10 is a plug that is 2 steps colder than a 6R12..... you're fine with the 6R12, if you go to a 6r10 without major mods, you may start fouling plugs and lose performance.... if your bike is stock HP or within 40-50HP+, no need to change to a colder plug... a good tune will dial you in....
Slightly longer, answer:
Here is a BASIC explanation of how a plug's heat range affects an engine...
Gasoline engines have an optimum combustion chamber temp between 500°C & 800°C. This temp is controlled by the heat rating of the plug. The tune will dial in the correct plug, but will not totally compensate for a plug too cold or too hot. The OEM HD plug is 6R12, selected because it provides the proper temp range for the design of the twin cam engine..... No need to change without major engine modifications....
No need to go colder unless you have added: higher compression, more timing, forced induction, alternate fuels, or sustained use of Nitrous oxide (note; all these things can affect the plug tip temp).
A plug too cold will foul, a plug too hot can cause severe engine damage.... better to err on the side of a colder plug.
General rule of thumb: Go one, full heat range colder for every 75-100HP added to the engine... A full heat range colder can reduce the combustion chamber temp by 70°c to 100°C
Just a down and dirty about plug heat ranges, hope this helps.....
6R10 is a plug that is 2 steps colder than a 6R12..... you're fine with the 6R12, if you go to a 6r10 without major mods, you may start fouling plugs and lose performance.... if your bike is stock HP or within 40-50HP+, no need to change to a colder plug... a good tune will dial you in....
Slightly longer, answer:
Here is a BASIC explanation of how a plug's heat range affects an engine...
Gasoline engines have an optimum combustion chamber temp between 500°C & 800°C. This temp is controlled by the heat rating of the plug. The tune will dial in the correct plug, but will not totally compensate for a plug too cold or too hot. The OEM HD plug is 6R12, selected because it provides the proper temp range for the design of the twin cam engine..... No need to change without major engine modifications....
No need to go colder unless you have added: higher compression, more timing, forced induction, alternate fuels, or sustained use of Nitrous oxide (note; all these things can affect the plug tip temp).
A plug too cold will foul, a plug too hot can cause severe engine damage.... better to err on the side of a colder plug.
General rule of thumb: Go one, full heat range colder for every 75-100HP added to the engine... A full heat range colder can reduce the combustion chamber temp by 70°c to 100°C
Just a down and dirty about plug heat ranges, hope this helps.....
Last edited by hattitude; Jul 1, 2017 at 11:35 AM.
Extreme HDF Member
Joined: Sep 2010
Posts: 14,744
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From: Phoenix '53, '88, '09 Big Twins
...nice
and just a FYI- the HD ECM uses "ion sense" which uses resistance in the plugs and wires to assess what is happening inside the chamber.
other than stock spec wires or plugs can trigger a check engine light- even screaming eagle and other "performance" brands
mike
and just a FYI- the HD ECM uses "ion sense" which uses resistance in the plugs and wires to assess what is happening inside the chamber.
other than stock spec wires or plugs can trigger a check engine light- even screaming eagle and other "performance" brands
mike
Extreme HDF Member
Joined: Jun 2011
Posts: 14,731
Likes: 2,536
From: Mountain Top, Alabama
I tip my hat to the HD Engineers that came up with their spark plug recommendations. They perform fantastic for me, look excellent every time I look at them, heat range appears to be right on the dime, so I am staying with them.
Special builds or engine conditions may need something different, but I am happy with the status quo.
Special builds or engine conditions may need something different, but I am happy with the status quo.
Road Warrior
Joined: Sep 2007
Posts: 1,252
Likes: 142
Ok I know I'm going to get slapped for this but, I fail to see how a small spark at the tip of an electrode that is hotter than the recommended heat range can cause engine damage. You are igniting an air fuel mixture. The entire cylinder is filled for a fraction of a second with very hot and explosive gasses. I just don't understand how a little dot of a spark can cause trouble. You want the fuel air to burn and explode don't you? I have been told this for years and I do follow it but the logic behind it just doesn't sit well. Its not like you are getting a plasma arc of electricity like that of and electric welder. Now slap me.
randy
randy
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Road Master
Joined: Dec 2009
Posts: 1,118
Likes: 5
From: Coweta, Oklahoma
I failed to mention that I have the M8 107 engine with 10 to 1 compression so if I read your reply correctly I think I should stay with the 6r10 plugs. Thanks for the education.
Road Master
Joined: Jun 2012
Posts: 1,062
Likes: 191
From: Boise, Idaho
Here is an article that explains Spark Plug heat ranges. It's not the spark that's colder or hotter. It's the plugs ability to dissipate heat.
http://www.enginebuildermag.com/2011...ug-heat-range/
http://www.enginebuildermag.com/2011...ug-heat-range/
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Road Warrior
Joined: Jul 2012
Posts: 1,996
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From: Cranbourne, VIC Australia
Ok I know I'm going to get slapped for this but, I fail to see how a small spark at the tip of an electrode that is hotter than the recommended heat range can cause engine damage. You are igniting an air fuel mixture. The entire cylinder is filled for a fraction of a second with very hot and explosive gasses. I just don't understand how a little dot of a spark can cause trouble. You want the fuel air to burn and explode don't you? I have been told this for years and I do follow it but the logic behind it just doesn't sit well. Its not like you are getting a plasma arc of electricity like that of and electric welder. Now slap me.
randy
randy
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Seasoned HDF Member
Joined: Sep 2008
Posts: 14,210
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From: San Diego, CA
Ok I know I'm going to get slapped for this but, I fail to see how a small spark at the tip of an electrode that is hotter than the recommended heat range can cause engine damage. You are igniting an air fuel mixture. The entire cylinder is filled for a fraction of a second with very hot and explosive gasses. I just don't understand how a little dot of a spark can cause trouble. You want the fuel air to burn and explode don't you? I have been told this for years and I do follow it but the logic behind it just doesn't sit well. Its not like you are getting a plasma arc of electricity like that of and electric welder. Now slap me.
randy
randy
As stated above it isn't the actual spark that is hotter, but the actual plug, because of it's lesser ability to dissipate the heat. If it is too hot it can much more likely cause preignition which of course can be very harmful, especially the earlier in the stroke it occurs.
BINGO.... you've been slapped...
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