Mallory's HEI (High Energy Ignition) Coil is a high-performance replacement coil for 1975-Later Delco Remy HEI distributor-equipped vehicles where the ignition coil is mounted to the distributor cap. Mallory Coils deliver the extra voltage required by performance engines. While stock HEI coil output drops sharply above 5000 RPM, Mallory HEI Coil #650-29212 stays strong to 5500 RPM. Mallory HEI Coil #650-29215 is best for engines that normally operate between 4000 and 7000 RPM. Mallory HEI Performance Ignition Coils are an economical way to increase the RPM range of any Delco HEI ignition, and they can be used with any of Mallory's HYFIRE IIA, IIIA, IV/A-C, or CD/IS Ignition Controls.