In general, with a sealed enclosure larger than recommended, you will have better low frequency extension, but *slightly* reduced power handling capability.

Here is a picture showing response of a sealed enclosure as volume increases past recommended size...

Green curve 1.77ft^3
Violet curve 2.68ft^3
Red curve 4.68ft^3

Above image was taken from this page: Speaker Response Curves

 

Just keep the gain down on that sub channel...according to the JL site you are over powering that sub, and with the bigger box your power handling goes down some.

 

Where did you see what power he was listing for the subwoofer, am i missing something ?

 

I instLl quite a bit of those subs , actually about 6 a week , which is bout 24 a month and I have heard them in lots of different ways. IMHO out of sheer experience with them , those subs do do best with the super small volume. I don't know how they are made to do this because it defies what you would think is conventional. But they have like no out put like at all when they go in larger boxes, and what blow me away is the .9ft 3 ported box for 12"s I was like no way that's going to sound like a$$ but it doesn't . Those are some very unusual subs , do what JL says and you won't be disappointed!!

For example I had a installer put a pair of 10s in a 1ft3 sealed box each separate chambers and it completely **** the bed. You could almost not hear the bass from the customers trunk , the guy came back upset . We ended up doing a diffrent box much smaller and it slammed