A spark plugs gap directly affects the tip temperature and the voltage necessary to fire the plug. Spark plugs traditionally leave the factory pre-gapped for their most popular application. However, a plug may fit hundreds of engines, from cars to golf carts.
Gapping the plugs to your engine’s specifications is important to prevent pre-ignition, detonation, fouling and poor fuel economy.
Even if the preset gap matches that required by your engine, it is always good practice to physically check the gap as it may have shifted during transportation (not all spark plugs are packaged in a way that protects the firing end).
Plug manufacturers warn against gapping fine wire spark plugs due to the fragile nature of their electrodes. Manufacturers say a fine wire plug will outperform a standard spark plug, even if not properly gapped. They will not warranty a plug who’s center electrode is snapped during gapping. However, a spark plug can only operate to its optimum potential if properly gapped. Proper gapping technique should be followed with any spark plug, but special care should be taken with fine wire plugs.
Proper gapping is especially essential in modified vehicles. The ignition process is affected by increased compression, fuel type, nitrous and high output ignition systems. A plug’s gap must be adjusted to account for these changes in engine conditions and ensure a successful ignition sequence. Opening the gap presents a larger spark to the air/fuel mixture, maximizing burn efficiency. However, after raising compression and installing a turbo, a smaller gap is required to ensure ignitability in the denser air/fuel mixture.