I have p3 shallow mounts there behind the seat in a supercrewsound box(1.2 cubic ft. i think) and a power acoustic 2200 watt amp that i got for cheap. they are loud but being behind the seat it sounds ugly.

 

Heh...that's an insanely "apples and oranges" comparison in terms of fairness. Take the same level of quality 15s, with the same level of engineering on the enclosures, coupled with comparable power and they will destroy the comparable 8s in terms of going "deeper."

Although there is a law of dimishing returns, a bigger woofer will be able to produce things that smaller woofers can't. It's just the way things work...

That said, I fully agree that the original questions is a total newb question that is almost impossible to answer as there are a million questions that need to be answered before it can be answered.

Carry on...

 

Alright with that said this gonna be my set up. I have a 03 screw and i am going to get a underseat sub box (1.2 cu. ft. shared) and im going to put polyfil in it. Im gonna get a kicker zx1000.1 amp for the subs and kicker zx650.4 amp for the door speakers, im either getting getting polk momos 6.5" or alpine type-rs 6.5"(any advice on these door speakers would be helpful). Also i have the pioneer deh-690ub head unit. Hope someone can help me out a little bit now with this info, what would be better 10's or 12's and which subs? I want them to sound good but get loud at the same time. Thanks in advance.

 

i have the type r's. they sound great.
go 12's if you can fit them.
there are tonnnnns of brands out there. its pretty hard to say what you would like