Well, let's get to the basics hopefully without boring you. The function of a spark plug is to produce a spark at the correct time to ignite the combustible mixture.  A spark plug is composed of a shell, insulator and conductor. It passes through the head into the wall of the combustion chamber and seals the combustion chamber against high pressures and temperatures for as long as 100,000 miles in some applications.

Why is the gap different for boost vs naturally aspirated?

When an engine has forced induction, like a supercharger or turbocharger, it increases

the cylinder pressure and can cause the spark blow out if the spark plug gap is too big.

Too small of a spark plug gap can cause the engine to run rough and have inconsistent

rpms. It is important to know the least amount to gap the spark plugs as well as the

greatest. Choosing the right type and temperature spark plug is very important.

What is spark plug gap?

Spark plugs are designed to have a spark gap which can be adjusted by simply bending

the ground electrode slightly. The same plug may be specified for several different

engines, requiring a different gap for each. Spark plugs in automobiles generally have a

gap between 0.024 and 0.071 in. The gap may require adjustment from the out-of-the-

box gap.

How Do I Gap a Spark Plug?

You gap a spark plug by using a special tool called a spark plug gap gauge tool. You

can also use another tool called a feeler gauge. These tools allow you to slide a

precision sized piece of metal in between the center electrode and the ground electrode

of the spark plug to measures the gap space.

In general, for a low boost application, around 14psi and under, you'll want to gap your

spark plugs 0.028" - 0.032". For higher boost applications we recommend to gap spark

plugs 0.020" - 0.026". If you still experience break up under boost, the rule of thumb is

decreasing your spark plug gap by 0.005" increments at a time until the desired stable

rpm gap is reached.

Spark Plug Heat Range.

One of the most misunderstood aspects of spark plugs is the heat range. One

misconception is that the heat range is related to the spark temperature or intensity.

Another common misconception is that the spark plug is designed as a heat sink to

“remove” heat from the combustion chamber. These ideas are both false. The spark

plug is heated during combustion and must dissipate that heat to the cylinder head at a

certain rate to avoid overheating the ceramic firing end. The spark plug heat range only

indicates the rate that the spark plug dissipates its firing end heat to the engine.

A hotter heat range spark plug has an insulator design with a longer heat flow path to

the metal shell of the plug. As a result, more heat stays in the ceramic firing end and

less is dissipated to the engine. A colder heat range spark plug has an insulator design

with a shorter heat flow path to the metal shell of the plug. As a result, less heat stays in

the ceramic firing end and more is dissipated to the engine. For a spark plug to function

properly, it must have a tip temperature high enough to burn off carbon deposits (self-

cleaning) and avoid fouling, while remaining low enough to avoid overheating the

ceramic firing end and pre-ignition.

For most vehicles, the factory recommended heat range is sufficient; however, on some

modified or special-use engines, alternative heat ranges may be necessary. Often hotter

heat ranges have been used to address a fuel delivery or oil consumption problem.

Installing a hotter heat range plug will reduce the pre-ignition safety margin, so it is

better to correct the mechanical or tuning issue instead of changing the plug heat range.

Below is a video from our friends at Procharger that summarizes the importance of the

correct spark plug in supercharged applications.