Vacuum controlled solonoid shutoff valve. Commonly used.
I inject before the MAF, as colder air is a higher density, thus increasing flow through the MAF that I want the car to be able to read. Most don't do this. I'm going to be playing around with a new TB soon, and porting directly into the base of it or the SC inlet itself.
There are advantages to injecting pre-rotor as well as post-rotor. It'* tough to make a decision, but alot of that depends on the mix you deliver. I'm switching exclusively to a 50/50 methanol water mix.
Most of my mix will evaporate before reaching the cylinders, but the evaporation effect will cool the air immensely in the process.
I'll move this to Forced Induction for you.