I have a bmw 328xi sedan and im gonna be running a single 12" fi q in a sealed enclosure because i wanted more sq the sub has the high qts option and the heat ring the website says .8-1.5 cu. ft what im wondering is what would be optimum size for the best sq for a wide range of music.

I would suggest the largest size you can fit.

I would suggest the largest size you can fit.

So do the 1.5?? Also i forgot to state im gonna be using a zed audio minotaur II at 2 ohm so roughly about 1300 rms

In all honesty I haven't ran the numbers but generally for good "SQ", meaning better damping and more extended low frequency response, you will want to aim for an enclosure on the larger side. The trade-off with a larger enclosure is less peak output.

Also keep in mind there is no such thing as "optimum".....everything is a serious of trade-offs, you just have to select which set of trade-offs best fit your personal preference and goals.

i found the cut sheets from fi it says 1.20 after displacement would that be better or should i just do the 1.5 after displacement?

In all honesty I seriously doubt you'd hear a difference between 1.2cuft and 1.5cuft