It is necessary to set the gap of a spark plug during installation as it could misfire, experience loss of power or cause poor fuel economy, according to NGK Spark Plugs. Not properly setting the gap can also foul the plug and quickly wear it down.
When installing new spark plugs, it is always best to check the specifications from the manufacturer, as explained by NGK Spark Plugs. If using plugs made of precious metal or fine wire, like platinum, it is important not to place too much pressure on the spark plug when adjusting the gap. This could damage the spark plug and other parts. Only adjust the gap by moving the ground electrode.
The gap distance may change if the engine has been modified, as stated by NGK Spark Plugs. If the compression has been raised or there has been a supercharger or turbo system installed, the adjustment is slightly different. In most cases, the gap should be reduced by about .004 inches for every 50 horsepower that is added. The exception is if there is a high power ignition system installed. In this case, the gap should be opened from .002 to .005 inches for proper performance.