Spring rate is established by the diameter and length of the torsion bar. Cranking it tighter might make the ride slightly rougher, but only if you take all the slack out, right up against the bump stop. The factory ride height setting was engineered into the vehicle. Anything else is probably a really bad idea.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!