OEM numbers
Toyota launch material confirms a standard Torsen limited-slip differential on the North American 2013 FR-S. Checked used assemblies are marketed by final-drive ratio rather than a reliable universal Y38 service number: 2013-2016 examples 4.10checked 2017-2020 manual example 4.30. Confirm transmission, year, housing tag and tooth count before purchase.Supersession
No supersession chain. 4.10 and 4.30 complete assemblies are gearing choices, not replacements that can be mixed without performance and calibration consequences.
Fitment
First-generation North American scope only. Standard Torsen does not mean every used assembly has the same ratio or condition. A 4.30 manual assembly changes acceleration/cruise RPM relative to 4.10. Verify transmission/year, ratio, input/output flanges, mounts, backlash/noise, leaks and crash damage. The IS300/IS250 crossover and speedometer assertions are held outside public copy pending Michael review.
Aftermarket options
Used complete 4.10 and 4.30 assemblies are the checked live paths. Clutch-type LSD centers, final-drive sets and cross-platform swaps require a separate setup/fitment audit; welded street use is not recommended.
Before you buy
Public guidance covers the verified first-generation North American Torsen baseline and 4.10-versus-4.30 identification only. Lexus/IS Y38 crossover fitment is excluded. Confirm ratio, transmission application, flange and condition on any used assembly.
Research and fitment sources
Supersede reviewed 8 unique research sources for this guide. 3 also appear above as a seller or official action and are not repeated here; 5 additional citations follow.
Research last verified .