yeah, don't spray before the charger, that'll cause serious longevity issues. Its meant to move air, not water. If you have a JRSC, you can use their injection point, otherwise, you'll have to make your own.

For turbo cars, the rule of thumb is 8-10" before the TB, but that wouldn't really be possible on a roots blower. Since putting it in at just one point on the plenum wont evenly distribute it, you may have to do like MrFatrear said and inject on every runner. Water needs time to atomize before its gets to the combustion chamber, so I'd recommend putting them as far back as you can get them from the combustion chamber on each runner.

What kinda SC is it?