Anyone have a list or link to some info on different year RX7 and Miata gearbox ratios. Looking for a drop in 5th that's closer to 1.0 than mine and also need to find out what mine is. Please respond. Looking at the 84-85 5th, supposedly drops in and is something around .85 or so.

 

The Mazda Motorsports catalog has all the ratios listed, and they will also sell you gears. They are expanding the tech section of their web page, but I don't think that the transmission section is up yet.
http://www.mazdamotorsports.com/weba...0001&langId=-1

74-76 RX-2,3,4,5 .862
77-78 RX-3,4,5 .791
79-83 RX-7 .825
84 RX-7 12A .758
84 RX-7 13B .807
85 RX-7 12A .807
85 RX-7 13B .711
86 RX-7 .711
87-88 RX-7 NA .697
87-88 RX-7 TII .762
89 GTUs .756
89-91 RX-7 NA Non-LSD .697
89-95 RX-7 TII and TT .719

Miata .814
79-82 626 RWD .860

 

Hey, do you know which of these listed will bolt into my tranny and which ones have to be machined? That 626 gear looks good but with 4.3's in the rear I don't want to kill my top speed. Still looking to get 150.

 

Some of my local EP racers use the 626 gear(s) in some manner, but I don't know the specifics. Give Mazdaspeed a call and see what they say.

 

Thanks for the input. I just registered with Mazdaspeed. I'll be looking for their tech page on transmissions and gearing. Anyone out there using the 5.12 diff gears? What's your top speed in 4th?

 

Speed in mph = (Rear tire circumference in inches * engine rpm) / (Transmisison gear ratio * Differential ratio * 1056)

If you don't want to bother jacking up your car and measuring your tire, this formula will be fairly close, although manufacturing tolerances vary in the tire industry:

Circumference in inches = pi * (Wheel diameter + (2 * (Aspect ratio * Tread width in millimeters / 254)))

For example, given a 205/60 R15:
Wheel diameter = 15 in
Aspect ratio = 60
Tread width = 205 mm

Calculated circumference = 77.55 in