RPMTimingControls 

 MSD Timing Controls are designed so engines with locked out timing or crank triggers can take advantage of an ignition curve. The weights and springs inside your existing distributor are removed and the mechanical advance is locked out so the timing is controlled entirely by the MSD Timing Control.
By controlling the ignition electronically, the timing curves can be set faster, more accurately, and with more adjustability than mechanical advances. The Timing Controls provide reliable operation throughout the RPM range, and must be used with an MSD 6, SCI, 7, 8 or 10 Series Ignition Control.