Hey everyone, I just wanted to start a quick thread so maybe it would be discoverable via a Google search after indexing so other people can find a quick solution to this without having to dive so deep into the net. I researched this just yesterday and after about an hour of searching I gave up on an exact answer to this question. I am wanting to install a 8" free air sub into the back of my TL in the factory location without ANY modification to the vehicle itself. Now I know this has been discussed on other threads and I have read them, however no one discusses the actual drop in(Plug and Play) size of the cut out in the sheet metal on the 4th gen TL rear deck. As all 8" subs are different I needed to know the exact dimensions that would allow the sub to just drop right in and allow me to figure out a mounting solution. Crutchfield has a great write up with pics on the removal of all the TL components including the rear deck sub. It just shows the ring opening but does not give the dimensions. So I wanted to give all dimensions here in one place where you will be able to find the answers you need if doing something similar. Please ask any questions in the thread and let me know if I leave something out so we can make it as complete a write up as possible. The following are the measurements for the factory 8" sub and its factory mounting bracket. I will provide a link to the Crutchfield page to see the pics of the TL breakdown. You must enter the vehicle type once landed on that page.

https://www.crutchfield.com/car/outfitmycar/mycar.aspx

8" Subwoofer top outer measurements without black mounting bracket = 8 1/2"
Actual mounting depth = about 3" after the trim ring is in place
Actual vehicle cut out diameter = 7 1/4"