Why is this performed on dragsters and highly modded road road/track cars?

saw it in action at santa pod - do not understand.

Weava

because after so long the NOS becomes crap after sitting in the pipes for too long therefore you get rid of the crap nos through the purge valve thus leaving good nos in the lines just before use

many thanks - not all kits have this though.

i have a street blaster 100 wizards of nos kit.

unfitted as yet, but why is this not a featured on it?

Weava