Just got done watching Trucks on TNN where a duramax diesel was upgraded with propane AND nitrous injection.

The host stressed how it was important to preheat the propane so that liquid propane isn't drawn into the cylinders, causing damage. No such modification was done to the nitrous though.

Why the discrepancy?

Masochist to Sadist: "Hurt me."
Sadist to Masochist: "No."

The nitrous is supplied as a compressed gas which only needs be regulated for use. 'Propane' or Liquefied Petroleum Gas is generally a blend of propane and butane. It has the handy ability to jump to a liquid phase at 'normal' temperatures and relatively low pressures. Releasing the pressure causes LPG to boil, therefore a heated converter is used to ensure gasification.