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
Speed Options
(Assuming 7500 rpm redline)
Stock:
- 3.636: 45/75mph
- 3.909 @ 8000 rpms: 45/74mph
- 4.1: 40/66/94mph
- 4.3: 38/63/90mph
Quaife 1:
- 4.1: 49/75mph
- 4.3: 47/71mph
Quaife 2:
- 4.1: 53/81mph
- 4.3: 51/77mph
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.
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 $700. Somewhat rare.
Speed Options
- (nothing lower than 3.636 seems to exist)
- 3.636: 38/62/86mph
- 4.3: 32/53/73mph (this one seems the likely choice, and also the easy ratio)
- 4.1: 33/55/76mph
Fluid
What fluid to run? Redline?
Starter
The later Miatas had a (3? 4?) pound lighter starter that is, in theory, a direct swap.
Driveshaft
The 99 carrier swap will bring a new slightly shorter driveshaft. The stock one is 11 lbs, the MSM shaft is 14 lbs. At some point someone made a CF driveshaft at about 8 lbs, but it's not available anywhere that I can find. Probably not worth it to bother. :)
Rear End
The car currently has the stock 1.6 rear end in it. No idea yet if it's a VLSD or open. I need to locate a new 1.8 pumpkin + axles to swap to.
Available Ratios
- 4.888 -- Mazdaspeed Motorsports has a kit (and I have one)
- 4.3 -- 99+ (I have one of these too)
- 4.1 -- 94-97
- 3.909 -- US 6-speed
- 3.636 -- Australian 6-speed (!? where do we get one of these)
In theory there's other options, but they may require some tweaking. See this Diff Info link for more options/info.
Differential
Once we get the 99 carrier in there, the options open up.
Torsen
Works great, holds up to a lot of power, cheap and available.
OS Giken
949 Racing worked with Bob Bundy on a high power option for the OS Giken diff. It's now available at 949 for 1734$. 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.
