Indexing Spark Plugs
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Joined: Feb 2010
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From: Greenfield, Wisconsin
Indexing Spark Plugs
Hey guys,
Just got done swapping my Autolite 3923s for NGK V-power 4644s. My coils and spark plugs needed to be cleaned and recoated in dielectric grease due to water getting in some of the spark plug wells when I went mudding, so I figured I would swap the plugs, too and pay attention to "plug index."
The idea of plug indexing is to position the gap opening of your spark plug towards the center of the cylinder to ignite the fuel more effectivly, instead of having it blocked by having the opening towards the cylinder wall.
When pulling out the old spark plugs in my bank 1 cylinders, I noted that the opening was in fact directed towards the cylinder wall, away from the injector by 90-120 degrees. When I went to put the new 4644 in, the opening faced the same direction. I think I will be picking up some indexing washers to work on getting the plugs indexed correctly. There are claims to a 5% gain in hp when indexing your plugs. I wouldnt have been suprised to see the gap in the spark plug to be a little off the center of the cylinder, but when I saw it was 120 degrees off, it seems like it could be making a difference. Im not looking for a huge difference here, but even if this means a gain of a few hp, it would be a cheap modification.
I never did check the index of the plugs in the bank 2 cylinders. After I realized my bank 1 plugs were 180 degrees off in all 4 cylinders, I figured I would need to get index washers regardless. I never paid attention to fuel trim with my old champion plugs, but I have noticed my bank 1 cylinders being leaned out a little more than the bank 2 cylinders. If the bank 2 cylinders are indexed correctly, is it possible that this index problem with the plugs in my bank 1 cylinders is whats causing the PCM to lean the bank 1 fuel trim out a little bit (up to 12% to be exact)? Im thinking this because if some fuel isnt getting burned, the computer will pick it up with the o2 sensors and lean out the mixture so all fuel is burned completly. Any input on this?
It looks like the indexing washers will cost more than my spark plugs do. Heres to give you an idea of what they are: They come in multiple thicknesses, in order for you to position the gap of your spark plugs to the proper positions
http://www.jegs.com/i/JEGS/555/40355/10002/-1
And finally, this picture will give you an idea of where you want your spark plug electrode to be facing. You want it facing towards the injector/center of the cylinder .... basically anywhere but against the cylinder wall
47lfo.gif
Just got done swapping my Autolite 3923s for NGK V-power 4644s. My coils and spark plugs needed to be cleaned and recoated in dielectric grease due to water getting in some of the spark plug wells when I went mudding, so I figured I would swap the plugs, too and pay attention to "plug index."
The idea of plug indexing is to position the gap opening of your spark plug towards the center of the cylinder to ignite the fuel more effectivly, instead of having it blocked by having the opening towards the cylinder wall.
When pulling out the old spark plugs in my bank 1 cylinders, I noted that the opening was in fact directed towards the cylinder wall, away from the injector by 90-120 degrees. When I went to put the new 4644 in, the opening faced the same direction. I think I will be picking up some indexing washers to work on getting the plugs indexed correctly. There are claims to a 5% gain in hp when indexing your plugs. I wouldnt have been suprised to see the gap in the spark plug to be a little off the center of the cylinder, but when I saw it was 120 degrees off, it seems like it could be making a difference. Im not looking for a huge difference here, but even if this means a gain of a few hp, it would be a cheap modification.
I never did check the index of the plugs in the bank 2 cylinders. After I realized my bank 1 plugs were 180 degrees off in all 4 cylinders, I figured I would need to get index washers regardless. I never paid attention to fuel trim with my old champion plugs, but I have noticed my bank 1 cylinders being leaned out a little more than the bank 2 cylinders. If the bank 2 cylinders are indexed correctly, is it possible that this index problem with the plugs in my bank 1 cylinders is whats causing the PCM to lean the bank 1 fuel trim out a little bit (up to 12% to be exact)? Im thinking this because if some fuel isnt getting burned, the computer will pick it up with the o2 sensors and lean out the mixture so all fuel is burned completly. Any input on this?
It looks like the indexing washers will cost more than my spark plugs do. Heres to give you an idea of what they are: They come in multiple thicknesses, in order for you to position the gap of your spark plugs to the proper positions
http://www.jegs.com/i/JEGS/555/40355/10002/-1
And finally, this picture will give you an idea of where you want your spark plug electrode to be facing. You want it facing towards the injector/center of the cylinder .... basically anywhere but against the cylinder wall
47lfo.gif
Last edited by rengnath; Jul 9, 2010 at 12:44 AM.