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Coil Ratings
Retro Rockets is an authorized PerTronix dealer.

Coil Voltage Ratings

     The voltage rating of a coil indicates the continuous output voltage the coil can produce without failure.  It is similar in concept to the speed rating on a tire.  If you have a "T" rated tire it means the tire can operate at up to 118 mph without failure.  So, the voltage rating of a coil and the speed rating of a tire are indications of capability.  You're not going to drive a tire at it's maximum speed rating all the time, and a 45,000 V coil is not going to operate at that voltage for every spark.

     The voltage required to send a spark across the electrodes of a spark plug depends on the conditions at the electrodes.  Parameters that affect the voltage are the gap between the plug electrodes, the density of the fuel/air mixture in the combustion chamber, and the turbulence in the chamber, among others.  The voltage required for spark at light throttle, low RPM, cruise conditions in a stock engine is probably no more than 15,000 V.  At wide open throttle things are a lot different.  The fuel/air charge in the combustion chamber is much more dense, turbulence is up as are cylinder pressures.  These conditions require more voltage to fire a spark at the plug.  Exactly how much more voltage is required depends on the specific engine.  Obviously, a high winding, big cam, high compression engine with high flow heads will require more voltage than a stocker.

     It is common practice to open up plug gaps over factory specs when installing an Ignitor and Flame-Thrower Coil.  With a standard Ignitor and Coil the gap can be opened about .005" over factory specs, with an Ignitor II and Flame-Thrower II Coil the gap can be increased about .010".  This will increase the voltage required for spark.  Keep in mind that when spark voltage goes up, more demands are placed on the electrical insulation of the rest of the ignition system.  Plug wires, rotors and distributor caps must be in good condition or you'll have sparks jumping to ground somewhere other than at the spark plug.


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Retro Rockets, P.O. Box 200, Norfolk, CT 06058
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