NGK IRIDIUM: More Durability and a Higher Melting Point compared to Platinum, better center electrode anti-oxidation and anti-erosion, improved ignition, superior anti-fouling, lower required voltage, new metal shell plating process for better anti-corrosion. One Step Colder plugs are recommended for cars with heavy modifications. The SRT-4 runs standard heat Champion spark plugs, the same as all other four cylinder Dodge models. These NGK plugs will get you smoother running and more power through increased efficiency and increased heat resistance. NOTE:Iridium plugs are able to use larger gap setting with less voltage. Some customers choose to regap these plugs to correct misfiring or tune for optimal spark -- do so at your own risk -- a slide-type plug gapper can damage the fragile iridium tip.