Originally Posted by j_man

Here is some info on all that - pulley, wheel & boss:

The crank wheel has nothing to do with the pulley. It has to do with the boss. If you need the wheel, you use the thinner boss. If no wheel is needed - you use the thicker boss.

The pulleys are independent from that (trigger wheel and boss) and are interchangeable ('94 - '05). There are two types of pulleys though (and are not year bound) - cast and stamped. One comes with a spacer for the bolts and different length bolts IIRC. So, depending on which pulley you get, use the matching bolts and spacer.

'94-'95 Miatas come stock with the thicker boss and no crank wheel.
'96-'05 Miatas come stock with the thinner boss and crank wheel.
The '96-'97 trigger wheel is used for misfire detection, the '99-'05 wheel is used for the crank position detection.

Pictures:

http://picasaweb.google.com/mx5files...WheelsCompared

The teeth on both '96-'97 and '99-'05 trigger wheels are positioned similar but the '99 one has 2 degrees advance and a little bit different shape ('99-'05 wheel is a circle, the '96-'97 one is not). So, the leading edges in the signal could be 2 degrees shifted, but they could be not either depending on the sensor positioning, etc.. Not sure about the trailing edges or whether the signal is inverted - I've never scoped a '96-'97 one).

Btw, a brand new OEM trigger wheel costs $6 at Mazdaspeed Motorsports