Mazda Miata NA (1990-1997): Drivetrain mods
NB 6-speed into an NA Confirmed
Two sources agree a 6-speed bolts in with shifter/plate changes; gearing needs attention.
Caveats: See the fitment page for starter, speedometer and rear-gear notes.
Parts: NB 6-speed manual transmission (with NB shifter)
Sources (2)
- Miata Drivetrain Interchange Guide — Randy Stocker / SoloMiata (fixjunk.com) (editorial; read 2026-10-15; full page read)
- NB to NA Miata Compatibility Guide — Redline Auto Parts (used-parts dealer; hands-on checks, own disclaimer) (vendor article; read 2026-10-15; full page read)
Limited-slip differential Reported
Hagerty says any NA is one phone call away from having a limited slip; Road & Track says NBs from 2003 use a Tochigi-Fugi LSD instead of the Torsen and that both beat an open differential.
Caveats: Check what your car already has: NA 1990-93 viscous option; Torsen optional from 1994.
Sources (2)
- Your handy (1990-97) Mazda Miata buyer's guide — Hagerty Media (Mar 2021) (editorial; read 2026-10-15; full page read)
- Everything You Need to Know Before Buying a Second-Gen Mazda Miata — Road & Track (Jun 2016) (editorial; read 2026-10-15; full page read)