Biggest Sub Box That Fits The Z
 

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Your going to want to have one custom built. Try a local stereo shop. Ask if they have any pictures of fiberglass work they have done. I know you can fit a 15 in the floor by removing the spare and building the floor up some but it will take some work and some fiberglass.

I've seen more than one z with a 15 in it

OP, take it from a guy who knows. This guys has done some wicked work himself :tup:

370z Photos by RDSAUDIOVISUAL | Photobucket

http://i1116.photobucket.com/albums/...z/IMAG0150.jpg

What can I say, I like a little bass...

In all seriousness, Homegrown check out these pictures. This is a car I did in 1995 that had a 15 inch in the floor. Was not that hard to do, can be done in a day or two at most if you have someone who knows what they are doing.

In this picture the everything in the trunk was removed then blasted with Rockford Fosgate sound dampening spray:
http://i1116.photobucket.com/albums/...Install/11.jpg

In this picture we had removed the metal brace that held the spare tire and then laid dynamat over the Rockford spray cut some MDF to fit over the wheel well and a piece to enclose the side so we could get the amount of airspace needed for the 15. One thing nice about the Z is that we don't have a crazy metal brace.

http://i1116.photobucket.com/albums/...Install/13.jpg

Here is a picture with the amp rack built and mostly everything installed:

http://i1116.photobucket.com/albums/...Install/14.jpg

Here is a picture with the beauty panels:
http://i1116.photobucket.com/albums/...Install/12.jpg

Then after that I made a piece of carpet that covered the floor so I could put things in the trunk.