Dual fire ignition module for mechanical advance. This module is optically triggered by an infrared light and a photocoupler. Therefore this system will provide a 100% stable ignition timing, at any RPM. The Mallory’s E-Spark can be used to drive any ignition coil (Accel coils recommended), or combination of coils with a total primary resistance of at least 2.0 Ohm. Coil recommendation: 2.0-3.0 Ohm for race applications and 3.0-4.0 for street/highway use. Note 1: A mechanical advance unit must be purchased separately. Note 2: With Mallory modules it is recommended to use Accel ignition coils. Note: The difference between single dual fire explained: – Dual fire – This is the way the earlier, pre-Twin Cam, engines work. A single coil is used and both spark plugs fire simultaneously. This is the simplest system. The ‘wasted’ spark is sometimes said to be horsepower robbing. – Single Fire – This is the way the stock 00-up Twin Cam engines work. Two separate coils will fire the spark plugs independently and only the spark plug of the cylinder that is on compression stroke will be fired. It is said that these engines vibrate less and can improve power. The effects will become more pronounced with hotter cams and higher RPM.