The easiest LSD that can drop into an s13 is an s13 LSD. J30 LSD into s13 bellhousing is a hack and will work but one axle stub will stick out about 2mm more than it is supposed to. J30 drops right into an s14 though.
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Epstein's little brother.
Car Specs:
White 95 Nissan 240sx SE SR20DET w/ 360whp
Red 2005 Nissan Sentra Spec-V
Human Specs:
Electrical Engineer