I currently have 2 JLw3D6 12" woofers and have found a third identical woofer (original series) for sale locally..

Now I have Maximum 5 Cubic feet for a box..

When i use WinISD and calculate having 2 or 3 woofers, 3 woofers always appears to be less in peak when using a 5 Cubic foot box than using 2 woofers.

When configuring the box size the levels come out the same when i hit about 6.5 Cubic feet, and increase up to 8 Cubic Feet.

Am I correct to say using a ported box with the space I have I am limited to having 2 12" woofers where adding a third one and making the internal volume smaller per woofer will not help me but go against me in SPL? Any feedback is greatly appreciated.

Going to a above 5 Cubic Foot Box is not an option, my current box i had to pop off the side to clear the opening to get it in the car, and then put it back on once inside the car.

probably not. u should gain even if a little. a 3rd sub will drop your ohm load lower so the amp should produce more power as well (if it can handle that ohm load that is). Unless u wire all subs in seriese and increase the ohm load then u probably wont gain, but that has to do with amp wiring, not having a 3rd sub in the box

Ya im limited on my amp..

I could wire the three subs,, 3 voice coils per side of the amp @ 2ohm and run a mono signal into it.. My Amp frowns on me now if i run it at 1.5ohm mono, flips into protection once i give it some juice.. The more i think of it i'm gonna stick with just the 2 woofers, and invest in a better amplifier.. wait till september/october when someone wants to part with a phd2 or phd3 after the competition season.

how much u wanna pay for a D2? no need to wait i part with mine all the time

Your amp is ok for 3 sub wire each coil in serie on the sub(12ohms) and put all sub in parrallel(4ohms). Your amp will give you 750wrms(maybe less) or 250wrms to each sub.
http://www.jlaudio.com/tutorials/wir...C_Series_3.gif