Progressive question
When the Air Door is closed, the air/fuel is also shut of, there is no/little cylinder pressure.
I do work with AID engines, with that case there is much more concern.
Lance
Factor in head loss, and the rate the pressure will drop when the solenoid closes and the line begins to empty, let's just make a safe assumption and slow that down to 1000 ft/sec. That would mean for a 12" line, after the solenoid closes, it would take .001 second to empty completely.
Now, at 6000 rpm, the crank makes a single revolution every .01 seconds. That's 100 times longer than it would take for the nitrous to evacuate the line.
Such a small volume of nitrous, evacuated in such an incredibly short time, seems incredibly insignificant in the scheme of things.





