Owners manual

GM HEI ROTOR BUSHING INFORMATION
IMPORTANT: If you are installing an MSD Ignition to a GM HEI (Internal Coil) Distributor, read the following
notice.
The Rotor Bushings used in GM HEI Distributors are made from high resistance carbon to help suppress
radio frequency interference. However, when the increased
voltage and spark energy of an MSD Ignition Control is added,
this high resistance may build up excessive heat which may
damage the cap or rotor.
This cap is supplied with a stock GM rotor bushing as well as
an MSD Low Resistance Bushing, PN 8412, which only has 1
- 3 ohms. The Low Resistance Bushing allows the secondary
voltage to be transferred from the cap to the rotor without
excessive heat build up. The stock bushing is black with a
bronze tip while the Low Resistance Bushing is solid bronze.
Stock HEI or a Performance Coil: It is recommended to
use the Stock Rotor Bushing in stock applications. The
higher resistance reduces the chance of excessive Electro
Magnetic Interference, or radio noise. If you have only added
a performance coil, use this Bushing as well.
MSD 6 Series Ignitions: GM used a variety of Rotor Bushings
with a large variance in resistance and in most cases with a 6
Series Ignition, the Low Resistance Bushing is not required.
In applications where the engine will be running at high rpm
for long amounts of time, it is recommended to use. If you
experience any problems within your cap and rotor, install
the PN 8412.
MSD 7 Series Ignitions: The Low Resistance Bushing is
required.
Note: The MSD Pro-Billet HEI Distributor, PN
8365, is supplied with the Low Resistance Bushing.
INSULATOR
ROTOR
BUSHING
COIL
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FRM33467 Revised 05/15