Re: GM DIS Upgrade using HEI Modules

Posted by shinyribs on Aug 07, 2011; 6:46am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/GM-DIS-Upgrade-using-HEI-Modules-tp3158051p3232592.html

Just a little bit of info in the HEI modules.I race Chevy engines and will not use any aftermarket distributors.I swear by the HEI.  On the later model modules,5 and 7 pins, GM introduced automatic ignition retard into the module itself.Hence to need for the extra pins.It was because of the "smog" motors at that time that would run extremely high combustion chamber temperatures to promote cleaner emissions.They used the automatic retard in the 5 & 7 pin modules to help combat detonation at upper rpms.The retard begins at 4500 rpm,if i remember correctly. I don't know of any difference between the 5&7 pin,personally.There may be some,I just don't know.But i do know that the good ol' 4 pin has no timing retard.So if you are looking for max performance you may want to consider the four pin. GM introduced the HEI in 1974,so if you go to an auto parts store and ask for an ignition module for that year model vehicle you should be able to acquire one with no problem.Small block and big block chevy's use the same distributor,and six cylinders used a different dist. but same module so any engine will have the correct 4 pin module.