when you remove the entire interior of a car and look on how the inner structure and outer shell come together often depending on the car there are large open pockets between the two layers of metal. you gotta bust out the torch to put the hole in it then build a baffle out from it. my 87 firebird had 8's there and i probably could have gone up to a 12 but i know a 10 would have fit. its all on what you use and how you use it. before anyone goes hacking into those corners be sure you arent going to hamper the cars structure if you cut into there and dont cut out any more than whats needed. after kirk cut the hole out they sealed the sections off by welding more steel in place and probably a reinforcing brace or 2. this is the corners where the firewall and kickpanel meet.
