I will snap some shots of my big three setup tomorrow. As for your setup.........
15"s are just a tad bit over kill. That is just my opinion. That sub box is HUGE, I dont see an ounce of trunk space left in that poor thing. Also did you cut that sub box in half? It looks like it on the right hand side of the port split it was cut through? I am guessing that is cause it was the only way, outside of maybe fitting that beast of a box through the back seat?
As far as power goes, you definitely need the Big 3 setup on your car running that stuff. Your amp is good, I actually had the 600+watt HiPonics one, it was a good amp. But I am getting another Kenwood Excelon X1-R to mate up with my X4-C amp. As far as a cap goes? That is something you may want to consider, but I would do the Big 3 wiring first. Caps serve a very limited purpose. You are best off doing the Big Three and then if that doesnt help, up your alternator next. Cause for the price of a good high end Cap, you are gonna pay the same for a 220amp Alt.
Myself, I am kind of conservative when it comes to my subs, I went only with 10's instead of my old 12" Punch I use to have, I wanted a cleaner sound over being just plain loud. But everyone has their tastes, I will never argue that.
Also what kind or gauge power wiring are you using to your amp in the trunk? It is recommended for an amp of your size to have at least 4ga power and ground wiring. My current wiring is setup on a 4ga design, but I have my new 1/0ga wiring for my new setup once I have the bass amp to put it all together. I am also going to be running Knutzconcepts 1/0ga 3 mini fuse block off the battery and a SoundStream Power Plant 1 to run all my power through in the trunk.
I will have 1/0ga wiring from the battery to the Power Plant and the ground will also be 1/0ga. The lines from the Power Plant will be 4ga to the amps, both Pos and Neg. It might be a tad overkill, but I would rather have a tad over kill over melting my amps cause they were under powered.
I know that might not answer all your questions, but if you have more, please post them. Sorry for the delay in replying back, was working on the car today and got tied up into that. I am sure you understand
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After looking at your pictures again, it appears you are running 4ga already? It looks pretty beefy, but looks can be deceiving. Also where are you running the ground off the amp? I am guessing from the looks of it, off the Strut Tower? That is usually a good location, plenty of good solid steel there. I actually redid my grounds, I use to have mine connected to the strut towers too, but it was a hassle if I ever had to work on the struts or anything. So I removed the backseat, both top and bottom sections and drilled a hole right above the center bolt that bolts the upper backseat down. I also sanded away all paint and primer to expose a good shiney metal surface to get the most optimal ground. The only small danger of where I drilled was the fact that is sits right in front of the gas tank. So I had to use an adjustable drill bit to go only a certain set depth to avoid any tank punctures.
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