Spark plug gap question???

[Petersubaru]

would anything be gained if the spark plugs were gapped at .030 instead of the stock .044...also how do the engineers come to determine the gap distance as being the best for the subaru

[ratfink]

would anything be gained if the spark plugs were gapped at .030 instead of the stock .044...also how do the engineers come to determine the gap distance as being the best for the subaru

 

From NGK:

A gap that is too small means that the spark duration will be very quick and the spark will be thin and weak. The consequences of this may be bad starting and high exhaust emission levels. This will result in an increase in fuel consumption. If the gap is set too large, the ignition system will not be able to cope with the demands and a misfire situation will occur. Some wide gap spark plugs have a longer ground electrode to accommodate a wide gap setting. These must be used where specified, as opening up a standard plug to a wider gap setting may result in the electrodes not running parallel to each other. This could result in abnormal and premature electrode wear.

 

I learned something, too.

[GeneralDisorder]

Larger gap = hotter, larger spark. Always.

 

But that has to be tempered by the strength of the ignition system - the coil's voltage output, and the ignitor's ability to switch on that much current. Too hot for one or the other will cause damage. Also the hotter the spark is, the more you will burn the plugs each time it fires. It's a balancing act, and really all you want is a 99.8% or higher probability of igniting the fuel. Once you acheive that, hotter spark is a waste of time. The engine's power comes from the controled burn of the fuel, not from the spark - it's only job is to start the burn. It either works or doesn't.

 

Use the recommended gap of .40 - .45

 

GD

[Petersubaru]

Both answers above have really answered my question and I was not going to mess with the stock recommended gap, ...I just never gave it any thought before until somebody mentioned to me that a smaller gap on the subaru will work better...I think the subaru ignition system has been quite able to handle the .044 gap with no problem and even larger gaps for that matter (not recommended)... over the last 20plus yrs and still having 4 subarus on the road, (carbed/spfi/mpfi turbo/mpfi) with a total mileage of about 650,000mi on them..I have never seen the plugs to show anything other then a " light tan" color indicating I think a good "burn", even though at times I have been negligent with maintaining the "tune-ups"