The Megasquirts (1, 2, and 3) can be set to read pretty much any wheel pattern imaginable, with any number of primary teeth and any number of missing teeth, with the following caveats:
1: The missing teeth (if more than one) must be sequential.
2: The spacing of the teeth must be even (there are some custom exceptions possible with the MS2/3, but that is rocket science.)
3: A second (cam) wheel is supported for use with crankwheels that have no missing teeth, and/or for fully sequential operation. This wheel is not required for batch-fire when a missing-tooth crankwheel is used. The camwheel can
be used whether or not the crankwheel has missing teeth.
With the MS2 and 3, higher toothcounts equal better spark accuracy, as the ECU will, in realtime, select the tooth which is closest to (but prior to) the calculated spark angle, and use that tooth as the trigger to launch the spark countdown timer. On the MS1, this feature does not exist. You can use any toothcount wheel that you wish, however you must specify a particular pair of teeth to be the trigger teeth, and these teeth must be far enough prior to TDC (and BDC) to accommodate the greatest possible spark advance. IOW, it is functionally equivalent to having a two-tooth wheel, with a phantom third tooth (the missing tooth) used for phasing. One exception does exist, in that during cranking, even the MS1 is capable of triggering on a specific, predefined tooth, as opposed to calculating all the way back from the "primary" trigger tooth.
A question: I understand that with the default configuration, the AEM is limited to a 12 tooth wheel. However I have come across some postings on various forii which suggest that it is possible to use more conventional wheel designs (such as 36-1) by setting up "tooth control table" which I don't quite understand. Examples:
36-1 teeth on the crank , 1 tooth on CAM