Lud is correct. Bottle heaters are really designed to give you consitant performance on back-to-back runs. One of the basic gas laws (Boyle's Law or Charles Law, I forget which) states that pressure and temperature are dirrectly related. This means when you do a run and use up NOS, the temperature of the bottle drops with the pressure. The heater can compensate by warming it back up until it hits the right pressure. If not, you get less NOS on each successive pass and your fuel/air mix can change and hp will drop.
Only really need it if you are planning on doing multiple runs quickly or live in one of those God-forsaken, cold, non-Texas states.
; )
[This message has been edited by David (edited 22 April 2000).]