well it's a dry system because it's not being injected to each port with fuel , but the manifold IS a closed system in that it is plumbed with tubes to the supercharger. as the manifold pressure rises from negative (vacuum) to positive (boost over 1 atm) the nitrous is introduced about mid way in the plumbing - by the time it hits the manifold it has apparently increased the pressure on my gauge by like 25 lbs. this is'nt theory ...it's actually happening. my best guess is that not many people use both forced induction AND nos. it is a closed air induction with no where for anything to go except to the ports , but the nos HAS had a chance to expand / cool / dense - ify the air headed that way for quite a distance (unlike a wet system direct port injection) the only reason i bring this whole mess up at all is because it's so suprizing to me...i never thought that kind of 'pressure' gain was to be expected most anyone ive spoken to has said that a slight increase in pressure like 1 - 3 lbs would be expected. the jets are tiny...no one runs .018 nos jets and expects to get a ton more ponys. it's been explained to me that a ''50 shot'' adding 50 hp by nos could be done with a single .034 jet dry...two .018's is just a hair less than HALF that...and it was described to me that these would be about a 25 hp increase (to play it safe what with some boost from the supercharger) you can feel the nos hit - it IS an increase and probably leaning out the air/fuel mix...who knows the fmu should perceive the pressure and correspond with more fuel.
either way i'm not driving the car with the nos until i get an understanding of how it's possible to see a 25 lb. increase in manifold boost pressure just from two teeny weenie little .018's