Drivetrain
Contents
Solo Rules
Drivetrain is virtually unrestricted.
Transmission
5 Speed
The stock Miata 5-speed transmission has been shown to have issues with high power levels in stock form. They're cheap as hell, though. Has anyone explored shot-peening/cryoing stock sets?
Ratios
3.136, 1.888, 1.330, 1.000, 0.814
Quaife Gearset
There is a 2500$ Quaife gearset available (+600$ installation) that's much sturdier, but rumors have that as potentially exploding as well under high power applications.
Ratios:
- Option 1: 2.564, 1.670, 1.273, 1.000, 0.794
- Option 2: 2.350, 1.550, 1.240, 1.000, 0.881
OS Giken Gearsets
[OS Giken apparently sells FC RX-7 gears that are then identical to the Miata internals and can be used there.
Ratios:
- 3-speed: 2.714, 1.742, 1.267
- 5-speed: 2.578, 1.772, 1.289, 1.000, 0.821
Miata-specific 3-speed Ratio: 2.604, 1.639, 1.228
Speed Options
(Assuming 8000 rpm redline)
Stock:
- 3.909: 45/74mph
- 4.1: 43/71mph
Quaife 1:
- 4.3: 50/76mph
- 4.44: 48/74mph (this gearset gives a much less annoying 5th gear too)
- 4.625: 46/71mph
Quaife 2:
- 4.625: 50/76mph
- 4.888: 48/72mph (almost 4000 rpms @ 60mph)
OS Giken 3-speed:
- 4.3: 47/73mph
- 4.44: 45/71mph
OS Giken 5-speed:
- 4.1: 52/75mph
- 4.3: 49/72mph
- 4.44: 48/70mph
OS Giken Miata Ratios:
- 4.44: 47/75
- 4.625: 45/72
- 4.888: 43/68
6 Speed
Some of the later Miatas had an option for a 6-speed, which is an entirely different design, and holds up to quite a bit more power. Not bulletproof, but a lot better.
I'm trying to contact several people to see about the mythical 3.3 ratio, and might end up being able to make one custom. This would be a great combo with the 6-speed.
Ratios
3.760, 2.269, 1.645, 1.257, 1.000, 0.843
Anyone ever make alternate gear ratios? Possible to change?
Cost/Availability
Seems to be around $700. Somewhat rare.
Speed Options
- (nothing lower than 3.636 seems to exist)
- 3.636: 38/62/86mph
- 4.3: 32/53/73mph (this one seems the likely choice, and also the easy ratio)
- 4.1: 33/55/76mph
TRE Box
There seems to be a guy who makes custom Miata transmissions. Taylor Racing Elite? The Springfield Dyno page references it, and it might be interesting to explore...
Jerico
Jerico also makes custom transmissions. Mckee's running one. Maybe get something like their 3 speed?
Fluid
What fluid to run? Redline?
Starter
The later Miatas had a (3? 4?) pound lighter starter that is, in theory, a direct swap.
Driveshaft
The 99 carrier swap will bring a new slightly shorter driveshaft. The stock one is 11 lbs, the MSM shaft is 14 lbs. At some point someone made a CF driveshaft at about 8 lbs, but it's not available anywhere that I can find. Probably not worth it to bother. :)
Rear End
The car currently has the stock 1.6 rear end in it. No idea yet if it's a VLSD or open. I need to locate a new 1.8 pumpkin + axles to swap to.
Available Ratios
- 4.888 -- Mazdaspeed Motorsports has a kit (and I have one)
- 4.3 -- 99+ (I have one of these too)
- 4.1 -- 94-97
- 3.909 -- US 6-speed
- 3.636 -- Australian 6-speed (!? where do we get one of these)
In theory there's other options, but they may require some tweaking. See this Diff Info link for more options/info.
Differential
Once we get the 99 carrier in there, the options open up.
Torsen
Works great, holds up to a lot of power, cheap and available.
OS Giken
949 Racing worked with Bob Bundy on a high power option for the OS Giken diff. It's now available at 949 for 1734$. Yoink.
Axles
Stock miata axles with the 99 carrier swap hold up to a lot of power. ABS Rings part # is BC4C-33-471. ~34$ each.
