I am buying 2 RL-i 8's in the next few days and I'm trying to come up with designs for the new box. I have a 2004 silverado regular cab, with a center console that houses a Fi/SX hybrid right now. Im thinking of the same concept but build the box downfiring and ported. The console would be much bigger than the actual speaker box, I would just have the box built into the bottom part of the console and maybe glass the top following the contour of the seats.

The box size would be 25*14.5*10 with a regular L-port. The total cubic foot after port and speaker displacement should be roughly 1.2 ft^3 tuned to 35 Hz. Is that too big for these subs? Any ideas for a box design would be appreciated. Im either going to do the console idea or build a box behind the seats and make a console that houses my amps.

how much port area are you planning?

12 sqin per cube??? isnt the rule 12-16 sqin per cube? so maybe 15- 20 sqin of port??

I built almost that exact setup, simple out of mdf. I think I could have gotten really creative with the fiberglass if the truck was here, but I built off of straight measurements. This was for a single 10" sub though:

I think we figured 1.25 ft^3 internal after port and speaker displacement. The port area is close to 20 in^2 if im not mistaken. It will be tuned to 35 Hz. Do all these parameters sound good? The only one im not sure about is the internal dimensions. Optimal car is 0.3 net per sub and im doing 0.625 per sub. Im just wondering if the bigger box will hurt their performance. Anyone with any experience with 2 of these in a box ported?

You should be fine my man. Going a little larger than the recommended net volume on the vented RL-i8 will afford you higher peak and overall output. This comes at the expense of producing a peak in your frequency response near tuning -- in otherwords, your response will not be as flat across all frequencies. This can be battled by lowering your tuning frequency a touch... But given the feedback from other car audio enthusiasts who have used similar enclosures, I expect you should be pretty well satisfied. If the box is too peaky, try lengthening your port to lower the tuning and see if that improves the situation.

Personally I'd lower the tuning, but that is me. It depends on your application of course. At 35hz it is going to be loud, but peaky at the same time. I of course would jump off the other end and try to tune her as flat as possible.