Ignition

Spark intensity is a function of ignition and voltage and has nothing to do with hot or cold heat ranges. A hot spark plug does not produce a hotter spark. Screwing in a set of hot spark plugs with hopes for a hotter spark is an incredibly bad idea. See above. Turbocharged or supercharged engines that generate increased combustion chamber heat from more atmosphere and fuel can benefit from a colder spark plug. As a general rule the experts at NGK suggest running one heat range colder spark plugs for every 75-100 horsepower added. Step up the ignition system to find a hotter spark.

Choice is Good

Pondering spark plug selection reveals a vexing array of electrodes, materials and surface types from the standard copper core single electrode to octo-tipped spark plugs promising horsepower from nano scale space technology. Back In reality semi-surface, multi-electrode and race-spec spark plugs are designed for a narrow range of operation. Indexing and electrode shape can affect combustion but don't expect giant performance miracles. If your engine and ignition system were designed to take advantage of the 100,000 mile durability offered by iridium, platinum or similar rare metal tipped spark plugs then spend some scratch and get the best. If your ride left the factory with standard spark plugs then rare and expensive metals offer no benefit. Manufacturers and the folks in the white lab coats that designed the engine in your ride make choosing the right spark plugs easy. Year. Make. Model. Engine. Done. Racecar you say? The spark plugs in a nitro-burning Top Fuel dragster or funny car might survive 1000 feet and a few seconds before melting into header plasma. In between the horrors of nitromethane and the daily driven appliance are the rest of us. Mild mods don't call for anything other than the spark plugs your ride left the factory with. A few steps into the cold heat range might lead to a foul but too far into the hot range can result in engine destruction. Heat range ratings vary by manufacturer. NGK spark plugs have a low number for hot and high number for cold. Bosch are rated the other way around. Spark plugs are usually pre-gapped but consult the service manual for the correct electrode gap and check conventional spark plugs with a feeler gauge if required. Exception! Do not gap iridium, platinum or similar noble metal spark plugs. That stuff is ready out of the box - especially if that box says "do not gap".