Spark plugs don't seem to come up around the campfire very often. Folks will go on and on about every other mod they've completed on their vehicle to date, but they never seem to dive into spark plug territory during their buildup recital. If you talk to an engine builder, however, you're sure to get an earful on the topic. Maybe this is because to the average 'wheeler, a spark plug is a spark plug is a spark plug. But to those in the know, it's a peek inside the engine to see how things are doing. Spark plugs offer a glimpse of what's going on inside the combustion chamber and can be a true asset in diagnosing engine dilemmas or in tuning an engine to perform at its peak.
Spark plugs perform two basic functions: They provide the spark to ignite the air/fuel mixture and they remove heat from the combustion chamber. The spark occurs between the electrodes and then generates the proper degree of heat to ignite an even burn of the air/fuel mixture. This is no easy job, especially considering that a spark plug has to perform this duty not only during cold starting but must withstand hours of engine operation at maximum power, all the while without misfiring during repeated acceleration. Now consider how often you change your spark plugs and figure that the plugs must sustain this operation for its entire service life.
The job of removing heat from the combustion chamber is accomplished when the spark plug acts as a heat exchanger by pulling excess thermal energy away from the combustion chamber and transferring it to the engine's cooling system. The rate of this heat transfer is determined by a spark plug's heat range, which is an index of its capacity to dissipate thermal energy and is typically a figure noted within a plug's part number. The different heat capacities of the plugs are designed to ensure that a plug will run between the desired operating temperatures for the engine. A plug's heat range can be deciphered by how it is constructed, such as the length of the ceramic nose and the type of material used for the insulator and the center electrode. A longer ceramic insulator nose permits a larger surface area to be exposed to the combustion chamber gases and therefore lets the heat dissipate more slowly. This is known as a hot-type plug, and is indicated by a higher heat range number, such as 7-10. A plug with a shorter nose offers a lower heat range number and will dissipate heat more rapidly. These are called cold-type spark plugs. By making sure you obtain the proper heat range spark plug for your application, you can reduce the chance of pre-ignition/detonation and firing end burn-out, as well as maintain a higher internal operating temperature to burn off excess oil and carbon deposits.
A number of factors weigh in on spark plug temperature and performance. Engine speed and load are proportionate to firing end temperature, as are higher compression ratios and forced induction. Advanced ignition timing and the air/fuel mixture can also have adverse effects on engine performance and plug temperature, as can the ambient air temperature and altitude.
Professional engine builders will change and inspect spark plugs often during the tuning process to achieve the optimum results. Computer-controlled engines will account for many of these factors using the various engine sensors that report back to the vehicle's ECM.
All spark plugs are not created equal. Hundreds of different spark plug designs exist for various engines and applications. Along with tip length, electrode composition also plays a large role in the operational characteristics of a spark plug. Many variants and special materials, such as platinum, copper, silver, gold, and yttrium, are used to create smooth, precise ignition, and some plug manufacturers use grooved or split electrodes to achieve a variety of claimed benefits. Another spark plug buzz word is resistance. Resistor plugs are designed with a conductive seal between the center electrode and the terminal stud to act as a resistor to reduce the transmission of pulses of energy to the ignition cables. The pulses in turn create Radio Frequency Interference (RFI), which is that high-pitched buzz you may hear upon acceleration and deceleration. Most computer-controlled vehicles use resistor-type plugs to maintain proper communication between the plugs and the electronic ignition.
Much can be learned by doing your homework before purchasing a new set of spark plugs. By shopping around and exploring the wealth of information available from spark plug manufacturers regarding their products, you may even notice some performance gains simply through selecting and installing a fresh set of plugs. Which plug is the best spark plug for your application? That's for you to decide. Establish frequent plug change intervals and don't be afraid to stray from your favorite brand. You may discover more performance out of your engine from where you least expected it. And that would certainly spark up a new topic around the campfire.