you dont need c02 but maybe you do if you track the car for consistancy , co2 allows you to run a lower spring than would normally work because the co2 i used to push the gate closed , lets say you want to launch at 5psi ( a safe level for traction on drag radials ) and want use the controller to hold it there , to do so you need a spring just shy of 5psi in your gate , problem is if you only have 5# spring and you stab the throttle you could unseat the valve with the backpressure before you reach your target and then your boost will build slowly , the co2 applies pressure to the top of the gate at the pressure you set at the bottles regulator (usuallly around 40psi) helps the spring hold the gate down and now you can build boost quick because the gate wont get popped open by back pressure
as for what you use it doesnt take much as the gate top is sealed and you only loose co2 when you are trying to control the boost , you do vent some off while on the brake and once you reach your target running boost it vents some to hold at the target level , biggest loss is leaks in the connections and if its leaking down and you leave the bottle open . i keep my bottle off except for when i'm making passes and the little 10oz bottle can last me almost all season , the bottle has a pressure gauge and you can watch that to see when its getting low and then get it refilled , i keep a spare bottle and the speed shop at etown can recharge them while i'm in the pits for around $6.00 a bottle
