how exactly do u go about finding peak note to use in port wars?

i know what to modify AFTER the port is made but how do u know which note to use? I know that you burp a couple hertz below what it peaks at but how do u know what to tune to in the first place?

i was thinkin about throwin the meter in the box and sealing it up..
but... if i do this, will the car's peak note effect the peak note used to tuned to for port wars?

or IS the proper tuning for port wars equal to SPL tuning?

I just don't know if what's goin on in the cabin area (front wave of the subs) effects what the pressure level being measured inside the box sealed up.

I have a wall that peaks at 50hz and am wondering if the port used to peak at 50hz is the proper tuned port for port wars as well.. and if it's different, how exactly do you go about testing to find out if what i've asked isn't the proper way.