Plug Gap
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Staging Lane
Joined: Jul 2010
Posts: 69
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Plug Gap I have been reading that some people have been setting their plugs at .040", when the owners manual calls for .060". May I ask why? The larger the gap, the better burn of the a/f mixture. why r .people setting them to .040"?
"larger the gap the better the burn" is not always true. You need an ignition system with enough power and ignition coils capable of sending enough spark energy and spark voltage to jump the spark plug gap. The greater the gap, the more voltage the coil needs to discharge otherwise you'll get a failed spark and a cylinder misfire.
Another big thing is rpm, as rpms get higher the coil has to fire more times per second and the coil needs a certain amount of charge time in order to output a full spark. When it doesn't fully charge and outputs a weaker spark, you can compensate with a smaller spark plug gap. Or another way of saying it is decreasing the spark plug gap decreases the chance of a misfire at high rpm, a slightly smaller spark plug gap is far better trade off than a misfire. Most everything with electronic ignition is 0.040-0.045" spark plug gap these days. In the day of points ignition with coils seeing less than 12v the plug gap was usually 0.030" to 0.035" max. With coil-on-plug ignition and an individual coil per cylinder there is plently of power to go around and there is not an issue with coil charge time at high rpm so 0.060" spark plug gap is not an issue unless you start running higher cylinder compression (higher compression ratio). And higher cylinder pressure requires more voltage for a spark to jump a given gap distance, so higher compression engines usually need to run slightly smaller spark plug gaps unless the ignition system is upgraded.
Another big thing is rpm, as rpms get higher the coil has to fire more times per second and the coil needs a certain amount of charge time in order to output a full spark. When it doesn't fully charge and outputs a weaker spark, you can compensate with a smaller spark plug gap. Or another way of saying it is decreasing the spark plug gap decreases the chance of a misfire at high rpm, a slightly smaller spark plug gap is far better trade off than a misfire. Most everything with electronic ignition is 0.040-0.045" spark plug gap these days. In the day of points ignition with coils seeing less than 12v the plug gap was usually 0.030" to 0.035" max. With coil-on-plug ignition and an individual coil per cylinder there is plently of power to go around and there is not an issue with coil charge time at high rpm so 0.060" spark plug gap is not an issue unless you start running higher cylinder compression (higher compression ratio). And higher cylinder pressure requires more voltage for a spark to jump a given gap distance, so higher compression engines usually need to run slightly smaller spark plug gaps unless the ignition system is upgraded.
Just use .050 for anything from bone stock to 600 RWHP. I've tried gaps from .040 - .060 when my LS1 was bone stock and with my 11.3:1 cr 427ci.
ZERO difference in idle, acceleration, WOT, etc, etc,......zero change in gas mileage too.
It just doesn't seem to matter at all with these little every day normal V8 engines, people keep thinking these LSx engines are something special...NEWS FLASH.....our LSx engines are nothing special in the automotive world, they are just another hunk of metal with 8 cylinders.
When you start spraying nitrous and boosting engines and making real power (over 600 RWHP)...then you can worry about specific gaps AND an aftermarket higher power ignition system.
.050 NGK TR55 or TR5......thats the best you're gonna do with any LSx type engine (NA, up to about 600 RWHP)
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