Chicagoland MG Club
Mallory Dual-Point Distributor
In this article we will examine yet another alternative ignition system for your British sports car, the Mallory Dual-Point Distributor. What makes the Mallory unique among point type ignitions, is, as the name implies, it has two separate sets of points to do the work of one. What are the advantages to using two sets of points? In the Mallory distributor, one set of points opens the primary circuit and the other closes it, giving a longer period of dwell (the period of time that the points are closed, expressed in degrees).
The dwell period is the time when the secondary windings in the ignition coil charge the magnetic field up for another high voltage blast when the points open (20,000-40,000 volts!). It can generally be said that the longer the period of dwell, the higher voltage the spark. On most four cylinder engines, the dwell period is about 60°, but the Mallory Dual-Point Distributor has a dwell period of 72°, so even if you choose to use your stock coil, you will still have a "hotter" spark, as the coil has more time to charge itself up than with a conventional distributor. This is accomplished in the Mallory unit by the following process. In the four cylinder distributor the point cam has eight lobes, and as it rotates, it opens the primary set of points completely, triggering the coil. Then the lobe rotates another 8° and opens the secondary set of points. Shortly after the secondary set has begun to open, the primary set closes, and the ignition coil starts charging even though the secondary set is still open. After the secondary set has closed the process starts again for the next cylinder.
Why not just crank open the points for more dwell in your stock distributor? You could, but this would have an adverse effect on the ignition timing and the points would wear in short order, as they are designed to work at a specified gap, all of which would result in a loss of performance and economy. Another feature of the Mallory Dual-Point Distributor is the fact that it has a full centripetal advance unit, rather than the part-centripetal, part-vacuum advance system used on the stock Lucas distributors. This feature may make it illegal for use on pollution-controlled vehicles (check your local and state laws before using this unit on the street) but makes it perfect for use with high performance engines equipped with sidedraft carburetors that often lack a vacuum port for use with a stock distributor. The Mallory unit is also easily adjustable for total amount of ignition advance, and comes preset at 28° allowing the serious enthusiast the ultimate in tune-ability. The Mallory Dual-Point is supplied without a drivedog or gear, which must be transferred from the old distributor. Mallory has been making high performance ignition systems since 1932, was even a popular modification to MG TCs when they were new!
Today there is a Mallory Dual-Point to fit most British cars, so if you're looking for the ultimate in high performance ignition systems, look no further than the Mallory Dual-Point distributor.
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