Possible Gains from tighter Spark Plug Gap?
TECH Resident
Joined: Sep 2009
Posts: 859
Likes: 2
From: Frozen Tundra, WI
I've heard that switching to a tighter gap spark plug can yield gains on mildly modified cars. I read that Alan from tick said that there was a noticeable improvement from switching from a .055 to a .035. Can anybody chime in?
Car has full bolt ons and a cam spinning to 6800.
Car has full bolt ons and a cam spinning to 6800.
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Spark plug gap is mainly determined by the power of the ignition and the mixture. A good starting point on late model vehicles is .045 and should be set with a plug gap gauge. Turbo or supercharged engines should use a smaller gap--.035 to start with.
All vehicles should have a placard under the hood which lists the timing, idle rpm setting and spark plug gap. Ignitions will vary from one car to another as to the amount of available power from the coil. The larger the spark plug gap, the more power necessary to jump the gap.
The larger the gap, the more power due to a hotter ignition of the fuel mixture resulting in more complete combustion. One method used by racing enthusiasts is to increase the spark plug gap by .005 and drive the vehicle. Accelerate and listen for an ignition miss. Continue to increase the gap until you experience a miss, and at that point reduce the gap by .003. This interpolation would give the maximum power and fuel consumption.
Another point on spark plug gap is that the gap increases with mileage as the plug wears. It varies somewhat with the variation of engines, but this is why the gap on all plugs should be checked every 30,000 miles.
Spark plugs are a window into the condition of the engine and the mixture. By inspecting the tip of the spark plug, the mixture, condition of rings and valve guides, and the degree of timing can be seen. Looking closely at the ground strap or electrode for color and condition is a major factor and the same with the porcelain center electrode.
A ground electrode that looks melted or rounded indicates too lean a mixture and possible detonation. A light gray color at the 90-degree bend in the ground electrode is ideal. The same color in the middle of the electrode means the mixture is slightly lean with would reduce power output. If the color is concentrated on the tip of the ground electrode, the mixture is too rich.
The center porcelain is also a big indicator. The tip closest to the ground electrode indicates the idle mixture. White is too lean, black is too rich and blistered off white is detonation. Optimum is light gray. The center of the porcelain represents the midrange or part throttle like cruising mixture and the deepest part of the plug indicates the mixture at full throttle.
Spark plug gap is mainly determined by the power of the ignition and the mixture. A good starting point on late model vehicles is .045 and should be set with a plug gap gauge. Turbo or supercharged engines should use a smaller gap--.035 to start with.
All vehicles should have a placard under the hood which lists the timing, idle rpm setting and spark plug gap. Ignitions will vary from one car to another as to the amount of available power from the coil. The larger the spark plug gap, the more power necessary to jump the gap.
The larger the gap, the more power due to a hotter ignition of the fuel mixture resulting in more complete combustion. One method used by racing enthusiasts is to increase the spark plug gap by .005 and drive the vehicle. Accelerate and listen for an ignition miss. Continue to increase the gap until you experience a miss, and at that point reduce the gap by .003. This interpolation would give the maximum power and fuel consumption.
Another point on spark plug gap is that the gap increases with mileage as the plug wears. It varies somewhat with the variation of engines, but this is why the gap on all plugs should be checked every 30,000 miles.
Spark plugs are a window into the condition of the engine and the mixture. By inspecting the tip of the spark plug, the mixture, condition of rings and valve guides, and the degree of timing can be seen. Looking closely at the ground strap or electrode for color and condition is a major factor and the same with the porcelain center electrode.
A ground electrode that looks melted or rounded indicates too lean a mixture and possible detonation. A light gray color at the 90-degree bend in the ground electrode is ideal. The same color in the middle of the electrode means the mixture is slightly lean with would reduce power output. If the color is concentrated on the tip of the ground electrode, the mixture is too rich.
The center porcelain is also a big indicator. The tip closest to the ground electrode indicates the idle mixture. White is too lean, black is too rich and blistered off white is detonation. Optimum is light gray. The center of the porcelain represents the midrange or part throttle like cruising mixture and the deepest part of the plug indicates the mixture at full throttle.
There is absolutely nothing that will be gained or lost from going from a .060 gap to a .040 gap...I can tell you that from experience with my bone stock car....then after I had my 427ci put it.
I tried them all with both engines. .060 - .040 performed identically.
Conclusion: There is not a single bit of performance change from .040 - .060. I have since been using .050, right in the middle.
Spark plug gaps can be the same (.050) for a bone stock LSx all the way up to a 600+ RWHP LSx.
Its when you start boosting and spraying an engine where gaps make a difference. And big *** high compression bad *** engines.
Also, there's really no such thing as a plug that is gapped a certain way....you just buy the proper plug and gap it yourself. TR55 and TR5 plugs are identical and may come gapped from the manufacturer differently, but you can change the gaps to whatever you want. And if you do buy a certain plug and expect it to be gapped a certain way...always check them before putting them in to make sure they are where you want them.
I guess the best of both worlds would be as big a gap as possible BUT still have enough power to make the spark. They make something that increases the power that goes to the spark plugs so you can make the gap bigger and still have sufficent power to make the spark.
.
I tried them all with both engines. .060 - .040 performed identically.
Conclusion: There is not a single bit of performance change from .040 - .060. I have since been using .050, right in the middle.
Spark plug gaps can be the same (.050) for a bone stock LSx all the way up to a 600+ RWHP LSx.
Its when you start boosting and spraying an engine where gaps make a difference. And big *** high compression bad *** engines.
Also, there's really no such thing as a plug that is gapped a certain way....you just buy the proper plug and gap it yourself. TR55 and TR5 plugs are identical and may come gapped from the manufacturer differently, but you can change the gaps to whatever you want. And if you do buy a certain plug and expect it to be gapped a certain way...always check them before putting them in to make sure they are where you want them.
I guess the best of both worlds would be as big a gap as possible BUT still have enough power to make the spark. They make something that increases the power that goes to the spark plugs so you can make the gap bigger and still have sufficent power to make the spark.
.
Spark plug gap is mainly determined by the power of the ignition and the mixture. A good starting point on late model vehicles is .045 and should be set with a plug gap gauge. Turbo or supercharged engines should use a smaller gap--.035 to start with.
All vehicles should have a placard under the hood which lists the timing, idle rpm setting and spark plug gap. Ignitions will vary from one car to another as to the amount of available power from the coil. The larger the spark plug gap, the more power necessary to jump the gap.
The larger the gap, the more power due to a hotter ignition of the fuel mixture resulting in more complete combustion. One method used by racing enthusiasts is to increase the spark plug gap by .005 and drive the vehicle. Accelerate and listen for an ignition miss. Continue to increase the gap until you experience a miss, and at that point reduce the gap by .003. This interpolation would give the maximum power and fuel consumption.
Another point on spark plug gap is that the gap increases with mileage as the plug wears. It varies somewhat with the variation of engines, but this is why the gap on all plugs should be checked every 30,000 miles.
Spark plugs are a window into the condition of the engine and the mixture. By inspecting the tip of the spark plug, the mixture, condition of rings and valve guides, and the degree of timing can be seen. Looking closely at the ground strap or electrode for color and condition is a major factor and the same with the porcelain center electrode.
A ground electrode that looks melted or rounded indicates too lean a mixture and possible detonation. A light gray color at the 90-degree bend in the ground electrode is ideal. The same color in the middle of the electrode means the mixture is slightly lean with would reduce power output. If the color is concentrated on the tip of the ground electrode, the mixture is too rich.
The center porcelain is also a big indicator. The tip closest to the ground electrode indicates the idle mixture. White is too lean, black is too rich and blistered off white is detonation. Optimum is light gray. The center of the porcelain represents the midrange or part throttle like cruising mixture and the deepest part of the plug indicates the mixture at full throttle.
You couldn't be more wrong.
lots of internet myths out there......if anyone has the ignition handbook by Dr Jacobs......the same guy that used to run the Jacobs Ignition company......but he sold it and it has turned to crap BTW.....in his book he recommends running as big as a gap as you can get away with......the bigger the gap.........more power.....but a bigger gap requires a very strong ignition system....which is where he came in with his ignition products......the best way to find your optimized gap is to experiment....no hard and fast settings to recommend
More gap is more energy in the kernel, up to the point
where you fail to jump the gap. Higher CR / boost does
that and you have to dial it back for the peak coil volts
you've got. But anything below reliable max gap only
costs you ignition energy in the hole.
where you fail to jump the gap. Higher CR / boost does
that and you have to dial it back for the peak coil volts
you've got. But anything below reliable max gap only
costs you ignition energy in the hole.
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