The Okada Projects' Plasma Spark is a spark plug boot (socket) specially designed and developed to work as a secondary ignition amplifier. An Okada Projects Plasma Spark for the 2002-2007 WRX/STI creates stronger sparks in a very short time (nano-seconds), creating a faster flame front and quicker light-off of the fuel mixture kernel to complete combustion. With Okada Projects Plasma Spark installed on your 02-07 WRX/STI, you can feel increased torque in low RPM and get more horsepower in higher RPMs. Installing Plasma Sparks is an easy direct bolt-in to the engine, no splicing or cutting into stock wiring: Simply replace the OEM Subaru spark plug with Okada Projects Plasma Spark Boots. Sold as a set of four (4).