The NGK R5671A-# is a NON Resistor Race plug with a non-projected tip. Using Non Resistor Plugs lowers the Resistance which allows more spark to the Electrode. This allows for a better more powerful spark. Using Non Resistor plugs can allow Ignition Noise to creep into your radio system and other electronics. It is two heat ranges colder for many Japanese import vehicles. When you increase power in your vehicle you need to use a colder plug to deter detonation and help pull heat out of the combustion chamber. NGK recommends one range colder for every 75HP-100HP increase.