How long does it take to burn out pistions with a 75 dry shot on my set up?
I would use the nos eveytime I drive the car 3-4 times a week for a few hours at a time

 

A 75 shot should be a pretty safe sized shot to spray. I would be more worried about constant bottle fill ups as nitrous cost per pound isn't exactly cheap.

 

You don't "burn out" the pistons with nitrous as long as it is tuned correctly. If you run it lean it will detonate, and fracture the stock hypereutectic pistons.

 

How much am i looking at for the full setup?

 

A setup with all the bells and whistles can easily tally you over a thousand bucks. I would like to say I have around 1250 in mine, the cost will escalate soon as I plan on changing some stuff and going from a nozzle to a plate setup.

 

Whats the point of a purge?

 

The purge solenoid removes the air from the main nitrous line. Otherwise, with air in the line, the fuel will hit before the nitrous causing the engine to go rich upon the initial hit and bog the engine.