23 Spline , center force clutch.Leave off a 2 step at 3500 rpm and runs 60 fts in the low to mid 1.6s on a 27/10 et street with caltracs and factory leafsprings.Has qa1 adj shocks all the way around. I shift at 7200 to 7400 with 4.10s and run 126 mph at 3470.Still a factory setup trans .