My first engine mod was the Airaid CAI. I put in the BBK 73mm TB a few months later and it made a big difference. I do not have a tune. You feel is beginning about 3k. Monster gains, no. Impressive gains yes. Hard shift to second gear would give a nice tire sqwalk before. With the TB, the car begins to fishtail now. I read all the reviews of yes/no to gains before I ordered mine. I can tell you first hand with no tune, it was worth every penny of the $400. I'm sure part of the gains are due to the CAI and the TB working together. How much I can't say but I can say the car came alive with the TB. (I'm trying to be clear here because, before I bought mine I had trouble finding a clear 'I have it installed with no tune and this is what it does' type answer. Good luck.
2016 Mustang Ecoboost Premium, Performance Package: Roush Quarter Window Scoops; Roush Jackal Rear Spoiler; Modded GT Wire Mesh Grilles; Eibach Pro-Kit Springs; Mishimoto Oil Separator; MAPerformance CAI; MBRP XP Catbacks; Drilled and Slotted Brake Rotors; BAMA 93R Tune; Royal Purple juice in everything!