for a B series actually a 50 trim is still good(but not for a really high Bseries revver like 9,000+). what b motor you talking about? if its a B18b then yeah LS cuz they dont rev....get you a 46 trim. Ever checked the compressor map on a T58 (Tso4)?mmm goodness.

my sr20 revs up to 7600 so the 50 trim is perfect for me at 15 and 20psi. 25psi i will start to choke the compressor.