Spark Plugs for Forced InductionNGK platinum spark plugs are a surface gap type plug used ideally for use in boosted rotary engines. The leading plugs are a colder heat range which reduces the chances of engine damaging detonation or "pinging". These are aftermarket plugs. Features: 2 leading spark plugs 2 trailing spark plugs with shims Less prone to "foul out" in richer forced induction applications