Autolite AR51-4PK High Performance Racing Non-Resistor Spark Plug, Pack of 4 Replacement racing spark plug used by many professional car drivers Specifically designed with colder heat ranges than the factory plug to enable performance modifications and handle intense conditions Contains an Yttrium-enhanced alloy to enable up to 8% reduction in side wire temperature for improved durability and less pre-ignition Features cut back ground electrode for improved ignitability of flame kernel Coated in an anti-corrosive nickel plating to prevent rusting