[Dilhol23]

I am thinking about putting in an aftermarket sub in my car(2008 G8 Gt) , in its own box with its own powered Amp. Question I have is do I have to get a 2 ohm sub since the rest of the speakers are 2 ohm? Or could I go with a 4 ohm sub? Would there be any difference in sound?

 

[Oldpoop55]

If you are going to use a sub box and an amp just for that box, you just need to match the amp ohms to the sub ohms.

I am using a 2 ohm setup in my GT.

 

[J Wikoff]

Since oldpoop answered the question, I'll just add a little advice:
If your door speakers are under stock power, aim for 400-600 watts rms from a subwoofer in the trunk.