1999 Miata in ITS?

[Marcus Miller]

I coming from the standpoint diffs were legal, not updating/backdating across spec lines... my bad.


Marcus

[WillM]

Hello all,

I'm a total IT newbie but have been around Miatas for a while. In the interest of sharing info, here is what I know about the hardware changes between the 94-95 and 96-97 Miatas:

94-95: 8.8:1 compression ratio pistons, ODB-I, 4-wire coil packs, optical CAS, factory rated hp @ 128
96-97: 9.0:1 compression ratio pistons, ODB-II, 3-wire coil packs, magnetic CAS, 2nd O2 sensor post cat, factory rated @133hp

Mid-way through '95, Mazda moved to the true 9.0:1 pistons and added the ODB-II electronics, but did not use them (no 2nd O2 sensor).

In 1996, ODB-II was put to full use, including the 2nd O2 sensor, which is post cat. I believe the additional O2 sensor makes up for most of the 5hp gain (allows better control over fueling, ie: leaner), but the increased compression probably helps a bit too. I'm not sure of the advantage, if any, between the 3 and 4-wire coil packs (4th wire was the tach signal).

The differences above are probably why Spec Miata requires different throttle restrictors for 94-95 vs 96-97 Miatas.