ahh that's a good question why not right before the turbo, well lets start with obvious reasons first. The turbo doesn't sit right on top of the manifold for starters, and it usually blows through an intercooler because intercoolers are a good idea (gm) and that's a long way to carry a mixture. Usually turbo guys will spray it before the throttle body which still gives it plenty of time to mix up with the air before getting to the motor. Turbo's are far more efficient than an m90 hence why a turbo gp will run 11's with just a turbo kit and some rockers. Now if you were to intercool an m90 then it's not about using the meth to cool its about using the meth to increase the octane. Then i would run some type of direct port meth injection if i were to go that route but i'd rather just pump in some e85 and go on my way. That's an awful lot of work for a little more octane. Plus depending on an alky injection system to run more boost is ballzy. If that ever fails you got yourself some pissed off pistons. See if my stuff ever fails i use is purely for timing, so my computer can pull timing out until i let off the throttle and investigate what happened. My aeroforce is programmed to set the warning lights as soon as i've hit .5 kr or higher and i'm happy to say it never lights up! Even on 21* of timing and a 3.2 pulley. That there is called a good tune! However every time i got to the track i'm cursed so i've never gotten a full run with everything working properly! it's very frustrating!
Meth will give great benefits in 100% mix it's pure science. It's a higher octane, so the more higher octane you run the harder it is to ignite the mixture, and you know what that means right? I can get meth at my local racetrack or you can get it online from places that sell race gas. I personally don't have a place to store meth so i don't order it. I just save the tune that i use when i do have it and load it right in. Most of the time you'll see me running water/windshield washer fluid since it's easy to find and cheap.