i owned a 90 LS (now own 91 DX)and LS have torque like a mother, but if i were to swap a motor, id just go with a 1.6 DOHC and save my self a headach, and boost like a mutha :)
out of a b16 and b18, id prolly get a b16. its a 1.6 so its more torque than a 1.5L And has vtec. the only reason why...