Subwoofer Depth measurement
 

I couldn't find a definite answer to this question using search-What is the maximum depth a subwoofer can be to fit into the stock 8" box? The Kicker CVR some people have used measures 4 1/4", is this the deepest you can go?

The sub depth also is dependent on how it is designed. If it has a hollow center on the magnet it will need some space for air to move out of the back. What sub were you thinking of?

I just measured the box. At the center where the bolt comes thru to the subs magnet it is 3.75" top mount depth. By using a 3/4 or taller spacer ring you can fit that Kicker and several other 8" subs. This allows for the back of the sub to have a gap before it hits the back of the box so the voice coil can be vented like Sapcecowboy mentioned above.

Kenwwod and Pioneer shallow subs measure under 3 inches so those would both work. Also JL makes a sub with a depth of 3 3/8" so that would drop in also. By using a 3/4" spacer ring you could use a couple of Kicker 8" subs and there also JBL and Polk. Pretty much any 8" sub except the extreme ones would fit, this is good info. Thanks for measuring, it saves me having to tear apart my car before I buy the equipment, I appreciate it!

Keep in mind with the TRUE shallow mount subs that they tend to give up even more of the lows then an 8 already does. That is why I do not ever bother mentioning them. I figure if you are wanting to use a sub you want a subwoofer and not a woofer which seems to be more where shallow mount subs play at to my understanding.

It is true that 8" subs don't play as low as 10" and those don't play as low as 12", but I have had all three in different vehicles and I don't really need subs that play 25hz frequencies anymore. I guess cargo space and hidden components have taken the place of big bass for me. Anyway, the new shallow mounts from Pioneer, Kenwood, JL, Kicker, and Earthquake are seriously impressive. They will play pretty low, enough for me, maybe not all people, and play loud. The JL 8W1v2-4 especially seems to be a really quality sub that is under 4" top mount depth and the Kenwood Excelon shallow sub also has great reviews.

can't go wrong with a JL Audio subwoofer