Subaru STi R-180 LSD DIfferentials
R-180 STi differentials come in various flavors:
2004 3.90 (L), 2006 3.54 ®. These have internal circlip retained stubs and are 27T splines. Datsun 510 pinion flange on L, STi pinion flange on R. The STi flange won't fit through rear x-member, has different driveshaft bolt pattern
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3.54 ratios are in the 2006 and 2007 STI.
3.90 ratios are in the 2004, 2005, and 2008 STI.
Torsen LSDs came in the 2007 and 2008 STI, others are clutch-pack LSDs. These are now $300-$500 used, but you need to solve the 27T splined stub problem before you can install one under your Datsun 510. 510s and Z-cars use 25T splines. Later Nissans use 29T splines.