What box volume is good for 6.5"s

I have a 92 caddy sts with the factory bose system. It sounds ok, but I want to upgrade. the front speakers are 4" and have their own box. I dont want to modify the car in case I decide to sell it, then I can just set everything back to factory. I am thinking of making a fiberglass mold of that box so I can be sure it fits in the car.

I know that there are alot of variables when it comes to matching speakers and boxes, but generally what is a good volume to start with when I build it? Should it be sealed or ported?

I am more into SQ than SPL, so I want to do whatever will sound the best.

Thanks for the input.

where do you want to put the 6 1/2's ?

in the front doors

by the way it is an Infinity Refrence 6010cs componant system.

if its a caddy you will more then likely have to replace the whole audio set up. These cars have integrated setups.... so you just cant "add" a component... you have to do the whole thing. Just a thought

yeah, it sucks.
I plan to get a set of 6x9s for the back soon, when I do I'm going to replace everything.

you may be able to play 6 1/2's in the door with no box at all .... depends on the speaker

yea most 6.5's are setup to free air in the door