MSD Digital GM High Energy HEI Distributor Module With Rev Limiter # MSD83647MSD Digital GM High Energy HEI Distributor Module With Rev Limiter # MSD83647 Using upgraded components, the HEAT HEI module produces high output for stock and MSD applications plus has a built in rev limiter that is more accurate and easier to set with the engine running. Features: Easily installs to non computer controlled (4 Pin) HEI housings Built in adjustable rev limiter can easily be set externally Advanced dwell control for improved high rpm