Yes, they're small, and they all practically look just alike, and even in the best of circumstances you're throwing them away and replacing them every few races, but spending a little time to make sure you have the best spark plugs for your race engine can make a big difference in performance.

The reason why—like everything else in life—is both simple and complicated at the same time. The simple reason is a spark plug that can't reliably fire the air/fuel charge in the combustion chamber means power-robbing misfires. And a spark plug that's poorly chosen can also fail completely, resulting in a dead cylinder or worse, such as severe engine damage.

On the other hand, a plug that works as efficiently as possible with an engine package can help improve power. It all comes down to igniting that first bit of the air/fuel charge—commonly called the flame kernel. The larger that initial flame kernel, the more quickly the flame front will travel across the combustion chamber. It works much the same way a stronger ignition will allow you to open up the plug gaps which can improve power. A faster combustion promotes greater pressure inside the cylinder and that equals power.

Heat Ranges
When it comes to racing, choosing a spark plug within the correct heat range is vital. Heat range doesn't refer to the amount of spark output, but the amount of heat that a plug can dissipate from its core. A hot plug uses a large insulator in the nose area to increase the amount of area of contact between the ceramic insulator and the metal casing. The insulator in a colder plug may be constructed of a different material designed to help move heat.

Also, it's not exactly the heat generated from the spark we're talking about. The plug is at ground zero of a small explosion every time the air/fuel mixture is ignited, and it's this heat from combustion that is absorbed by the plug and can really affect performance.

A cold plug can more efficiently move heat absorbed by the tip of the plug from combustion through the insulator and to the metal shell where it can then, in turn, be absorbed into the cylinder head where it can be negated by the water flowing through the coolant passages.

Finding the right heat range will be the difference between an engine that runs happy throughout the night, one that fouls plugs at the worst time or one that suffers from self-destructive detonation.

A problem with fouling spark plugs can come from running plugs that are too cold. This is because no race engine is perfectly efficient. Oil can make its way past the rings—especially the super thin, low tension rings that are currently so popular in racing—and into the combustion chambers. Likewise, some of the byproducts of combustion may remain in the chamber after the exhaust valve has closed, which can lead to carbon buildup.

Carbon buildup on the chamber walls, the piston top, or even the valves is no big deal, but carbon buildup on the spark plug can keep the electricity from flowing properly from the tip to the electrode. And in plain English that means no spark, and you've got a fouled plug.

That's why spark plugs are designed to operate within a certain temperature range while the engine is running that is hot enough to burn off any carbon that accumulates on the plug and essentially becomes self-cleaning. If the plug is too cold, it will wick away heat too fast and won't get hot enough to burn away any carbon buildup.