With 28 years of working on car, bike and truck engines, I've personally found NGK plugs are a safe bet for your standard running engines. They match most factory specs closely for gap and temperature rating and are known in many cases to function better than supposedly 'uprated' or 'high performance' plugs. Unless you know exacrly what you're doing and what the codes and numbers on a plug mean, stick with NGK recommeded plugs for your engine is my feeling.