dear bros

just want to change throttle body to a bigger one to get more power.

but i am wonder how much more power will i get by changing throttle body to 67mm (tritec 1.6 NA engin), any other issue will bring to my car if i change it to 67mm?

thank you

As long as you change the other parts too, you'll see better gains.
Ie,
Intake
Intercooler etc

Lohen includes a 58mm throttle body with their Stage 3 kit for the Cooper / One.

Seems to me that a larger throttle body would be one of the last engines mods to make.