Installing a fresh set of the "right" spark plugs is one of the easiest and least expensive ways to maximize the performance from an engine. On turbocharged engines, we have seen power gains ranging from a few horsepower all the way up to 100 horsepower when worn or fouled plugs were replaced with a fresh set. On naturally-aspirated engines we've witnessed gains as high as 10 horsepower. Since every performance enthusiast is always looking to maximize the performance from their engine, understanding spark plug technology is a must. Considering that a fresh set of the right plugs may increase your gas mileage by 10 percent, this is one performance upgrade that can definitely pay for itself quickly.

Function of the Spark Plug

The primary function of the spark plug is to create a spark that initiates the combustion process within the cylinder. While this job sounds simple enough, the environment where a spark plug lives is far from friendly. A spark plug is subjected to electrical voltages that may approach 40,000 volts. In addition to the electrical shock, cylinder pressures may exceed 300 psi during combustion. At the same time, in-cylinder temperatures can soar to 2,500 degrees Celsius then instantly drop to outside temperatures when cool fresh intake air is drawn into the cylinder. If you have ever poured hot water in a chilled glass or ice cold water in a hot glass, then you've seen first hand the damage that can be done by thermal shock or loading. Yet through all this, a quality spark plug can survive and thrive.

Ignition System Overview

"A number of components linked together for the purpose of generating a spark in the cylinder" is probably the most accurate description of the ignition system. Ignition components include the battery, ECU, coil, distributor, cap, rotor, spark plug wires and spark plugs. Depending on the type of system (direct-fire, wasted-spark, conventional), your car's ignition system contains all or some of the listed items. In any case, all gasoline-engine systems include spark plugs. Understanding and selecting the best spark plugs for your application ensures that the spark plugs don't become the weakest link in the chain.

A Better Plug

So what makes one spark plug better than another? Of course, this depends on what is important to you. If you are looking for maximum performance, there are certain spark plugs that are designed to minimize misfires or maximize the combustion of the air-fuel mixture. If you are looking for maximum service intervals, there are spark plugs that are designed for limited gap erosion, allowing them to function two to five times longer than conventional plugs. If you are on a limited budget, there may be plugs available that provide a heat range that's optimized for your engine's modifications and your driving style. When it comes to choosing the right plug for the job, knowledge is power.

Hot or Cold?

One of the most important considerations when choosing a replacement spark plug is being sure that the correct heat range is chosen. If the replacement plug that is chosen is too cold, fouling occurs. This leads to misfires, poor performance, increased emissions and reduced fuel economy. If the replacement spark plug has a heat range that is too hot, the results are even worse. The spark plug can become so hot that its temperature ignites the fuel before the spark ever has a chance to fire, this is termed "pre-ignition." Pre-ignition can lead to severe engine damage or melted electrodes at the very least. Most tuners end up using a plug that is one to two heat ranges colder than the heat range of the original equipment spark plug. However, ultra-high boost pressure or ultra-high compression ratios may require spark plugs that are three to four heat ranges cooler. Since the side effects of choosing a plug that's too cold are much less problematic than the results of choosing a plug that is too hot, it's always safer to start with a colder plug.