1. Venerable Miata (and 1st gen RX7) 5-speed. This box is nearly bullet proof, even in forced induction applications. Has been upgraded throughout the years, including helical reverse and dual-cone 2nd gear synchro in '94. Curiously, in '99, the retaining rings that keep the gears from 'overthrowing' were removed from the shift rods. PPF mounts from the passenger side.

2. MX-5 (2006+) 5-speed. This is a new version of the same venerable 5-speed box - exactly the same internals, and intermediate case, with a new bellhousing and tail shaft. This trans adds dual-cone synchros for 3rd and 1st, I think... it's been a while since I've been in one. This is the box that's so highly regarded by MX-5'ers, but it caused us nothing but problems when we tried to race them in the MX-5 Cup. The cases were twisting, and 3rd or 4th would regularly shear off. There was heavy evidence of the case twist. I don't think any of this would be a problem in a street application. PPF mounts from the driver's side.

3. Aisin 6-speed for '99-'05 Miata/Miata Turbo. Generally regarded as bulletproof, not raced as widespread as the RX-8 - but raced enough to know it's a good box. As noted above, has a better 4th gear ratio than in the RX-8. PPF mounts from the passenger side.

4. Aisin 6-speed for '04-'08 RX-8. Generally good reputation for street use, but very fragile for racing use. Big problems with 3rd/4th being overthrown and losing their shift-keys detent *****. Very poor metal quality for both steel and aluminum parts. Quick wear on shift hub slider teeth and matching gear teeth - causing grinding. Doesn't last very long in race use. We've made some upgraded parts that make them last better (one recently finished the NASA 25hr race,) but still a compromised design. At best, our fixes only extend the inevitable demise. PPF mounts on the driver's side.

5. '06+ MX-5 (and '09+ RX-8) 6-speed. Single case, or toploader design (much stiffer structure than the mult-part caes on the other designs.) Very large gears, much bigger than the other gearboxes. Dual cone synchros on all but 5th, 6th and Reverse. The weakest link on this gearbox is the 3/4 shift fork. It's weak metal, and breaks quite easily. We have made a billet replacement for racing use, and I hope that the new RX-8 box has an upgraded part. We've passed on everything we learn to Mazda, they are acutely aware of this issue. There is an adjustment for 3/4th shift throw, and this being mal-adjusted is the cause of most complaints from street users - the dealers can't do anything about it, because it's not in the shop manual... we've worked with Mazda, and it should be added. There are also three plastic bushings that break when the trans gets to racing temperatures. Finally, the 3/4 shift hub is prone to cracking under racing use. The gears are very durable, and the teeth on the hubs/gears stay sharp even after two seasons of racing. MOST of this gearbox is bulletproof, and Mazda is aware of the weak links... I'm sure they have integrated some of these fixes into the RX-8 version of the gearbox, knowing the weight/hp increase that it will need to hold. I can only assume that they delayed putting it into the RX-8 until they learned as much as possible about it. I would confidently say this is the best gearbox of the bunch. PPF is mounted on the [i]driver's[i] side of the case.

Sharp readers will note that on both the 5-speed and the Aisin box, in the Miata application the gearbox is trouble-free, and the RX-8 and MX-5 applications of those same boxes, they don't hold up as well. REALLY sharp readers will notice that the PPF mounts on opposite sides in each case... making me believe that's too much of a coincidence. I think the side it's mounted on makes all the difference in how the tranny will last.

Overall, I'd be happy they went to this box... it should be much better than the current one, especially for street and autox/occasional track use.

As soon as we get one here to play with (hopefully very soon,) I'll let you guys know if the improvements made it in there, and how it holds up for us on the track.

1. Venerable Miata (and 1st gen RX7) 5-speed. This box is nearly bullet proof, even in forced induction applications.