Chicagoland MG Club
Mallory Dual-Point Distributor - #2
It has been brought to my attention that there are some errors and slight misrepresentation in the previous article. The first error is the statement that first points open gives spark. Actually, you don't get the spark intil the second set of points opens to break the ground contact. Degrees of dwell expressed in that article may be apparently at the crankshaft, while common notation gives dwell angle at the distributor (half as much). What you measure with a dwell meter is dwell angle at the distribuitor. Cranking open the points gives less dwell, not more. Changing the dwell does not screw up ignition timing, if you just set the timing after setting the dwell. Enough about that article.
I have a Mallory Dual Points (non-vacuum) distributor in my car, model 2332001, and I have the spec sheet. For the 4-cylinder model dwell for each set of points is 32 degrees. There is 8 degrees offset between the two sets of points, so the total effective dwell is 40 degrees (at the distributor). You can double those numbers for dwell angle at the crankshaft.
For comparison, the Mallory Single Points 4-cylinder model has a dwell angle of 35 degrees. There is not a lot of functional difference between 35 or 40 degrees dwell. In fact the stock Lucas distributor has 60 degrees dwell. I have seen race engines running up to 9000 rpm with a single points distributor and never miss a spark. I can remove one set of points in my Dual Points unit, reverting to 32 degrees dwell, keeping ignition timing the same, and run up to 7500 rpm with no noticable difference in performance. I am certain you would have to have the car on a dynomometer to notice any power difference due to the dwell angle (assuming the spark timing is the same). Increasing dwell is NOT the reason why Mallory uses dual points.
For a street engine the dual points has very little functional advantage over single points, and vacuum type is generally better than non-vacuun type for low end performance and throttle response. A new distributor can of course be better than an old worn out one. Perhaps the second best selling point of the Mallory Dual Points distributor is the wow factor in the name. Third best selling point is constructive pricing, where the initial purchase price is lower than a new Lucas distributor (but the long term maintenance parts are more expensive). But the best selling point, and the real reasons for using dual points are improved life, long term stability and reduction of service calls.
For a description of how the Dual Points Distributor works, and why, check here:
You can see a 160,000 mile user report here:
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