I got this from the snow performance website FAQ:
Pre- or Post- throttle body/carburetor?
• Performance: It makes almost no difference. Before or after the throttle plate(s) won’t change the effectiveness of the fluid. A given amount of fluid will absorb a given amount of heat, whether it is done more before or after the throttle plate really doesn’t matter.
• Installation: It is usually easier to inject pre-throttle body in the intake tube. Easy access, no solenoid required (unless rear-mounting a reservoir). On a carburetor, it can actually be easier to use the #40050 carb spacer plate and a #40060 solenoid for a bolt-in installation. These components are included in our RT and MC series systems.
• In a blow-through carburetor setup with an air-box enclosure around the entire carburetor, injecting after the carburetor is preferable.
Pre- or Post- Supercharger/Turbocharger?
• Centrifugal/Turbo: (Procharger, Vortech, Paxton, Powerdyne, Rotrex, etc.) Never mount an injector nozzle before a centrifugal supercharger or turbocharger compressor. Sending fluid through the compressor wheel that spins anywhere from 50,000rpm to 250,000rpm can erode the leading edges of the fine aluminum, as well as serve to reduce the atomization. Instead of a fine mist, the compressor housing will create a river of fluid along the outside wall that means we get less benefit and use more fluid.
• Positive Displacement Supercharger: Roots style (B&M, Eaton, Magnuson, etc.) or twin screw (Lysholm, Kenne Bell, Whipple, etc.) Mounting the nozzle before this style of blower is perfectly safe and actually provides some additional benefits. The small amount of water-methanol fluid isn’t harmful to any rotor seals or surfaces or coatings, and it helps to seal the clearances and condense the air some more, resulting in a more efficient output. Additionally, it keeps the rotors and housing MUCH cooler, which reduces heat transfer to the rest of the intake and air charge.
