I'm not an electronics expert, but..
A Pertronix ignitor is a simple electronic ignition system, it replaces the points with a Hall-effect sensor and a plastic ring with 4 magnets in it. This ring sits over the distributor cam, under the rotor button.
As each of the magnets passes the sensor it interrupts the coil's primary current, causing the coil's H/T secondary circuit to give the usual spark to the rotor.
However, there is more spark energy available because the switching occurs faster than it did with points, there is also more dwell (time for coil to build up power). You can increase plug gaps to .035" or more, even with a stock coil.
Normal bearing wear in the distributor has little effect on it.
Net result is timing doesn't vary, as there's no wearing parts- it doesn't slowly get retarded like it does with points.
Check this site for more info,
http://www.vintageperformance.com/retro ... /index.htm
if looking for Mini applications go to `distributors' page and click `Lucas'.
<EDIT> You can buy from this site, cheaper than MiniSpares or anybody in Oz.
They won't ship their wire sets or Flamethrower coils overseas though. So I just fitted a Bosch GT40-T coil and Bosch leads, I got at SuperCrap.
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
