I agree guys, unless you have a valid ram air scoop. Or any pressure changing device that is connected to your intake. A good ram air will produce elevated pressure and no MAP reference pressure regulator can make your mixture go lean.
Bill Jepson

Not really, Bill.  Even at the incredible speed J of my Velocity 20B (let’s say 160 Indicated) the ram pressure is about 1 ¼” Hg – IF the scoop and ducting are 100% efficient.  Not going to have a noticeable effect on tuning.

Al G