Hey guys, there is no such thing as a dumb question. If he knew the answer, he would not have asked, give the kid a break. Not everyone knows everything about everything like you guys.
As for the NOS question....
here ever used it? - Yes, on my 1998 Mustang GT. I was running 250 horsepower shot (Meaning when you trigger the NOS, it instantly hits 250 extra hp.
Just curious, but how much of a speed boost does it give on average? - Depends on how much NOS your engine is set up to handle. Most stock engines can get away with 75 hp boost. After that, you need forged pistons, upgraded fuel systems, cold cold cold sparkplugs, etc. 75hp boost, it makes a mustang feel like your stomped gas pedal was actually half way, and you just mashed your pedal. At 250hp boost, you hit the gas pedal for the second mildly modified 4.6L V8 you have under your hood.
how much does one tank of it cost, if the tanks vary in size, how about one for a 15 second boost? - My 10lb cost $35 each to fill (Ran tandem tanks). I could get about 15 hits with it on a quarter mile, but that was only hitting it in 4th and 5th gear. Any lower, and my back tires would give it up.
Biggest tip I can give is READ READ READ before you use NOS. If you go lean on fuel, you burn heads, pistons, and worse. If you go too rich, you blow apart your intake, airbox, and every air operated sensor in your intake (Like I did. Ford's composite intakes don't like nitrous explosions in them.)
If used properly, it works great. If abused, it is costly.