How can I get more volume?

I am trying to keep my car in the 500 watt category for DB Drags, I am running two Xtant amps 3.1 and 4.4, 1 Xtant 12" DVC sub, and Boston Acoustics 5x7 speakers in the front and back of my car.  The Sub is wired to 2 ohms and hits pretty hard, the box is a Fiberglass home built box.  I tested with my DB meter and it hit around 125 yesterday, I am trying to get into the 140-145 range.  Does anyone have any ideas how I can increase my DB without blowing up my system?  Thanks for any ideas you can give.

The only ways you can gain volume is with more power, or more surface area (i.e. more woofers) or more efficient woofers. You already said you want to remain below a given power rating, so this leaves surface area. Translation? More woofers, or more efficient woofers... that's all you can do, man. If you are presently using a sealed box, a vented enclosure will give you a 3dB gain, at one frequency, with less gain above and below that frequency.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

The 5x7 size is going to limit your number of choices. A 6" or larger can be made to fit. Xtant lists it's subs in the low 90 db sensitivity range which is about average. The Boston 5x7 are about the same. Car audio speakers are not always the most sensitive. There are many professional drivers that are 100db and higher. JBL, PHL, B&C and the all powerfull TAD. The drawback is impedance. The standard is 8 or 16 ohms. The infamous Mark Eldridge has used pro M/B and horns for years. Hense using a 50 watt amp on a pair of Image Dynamics or USD horns. These HLCD's are 106db efficient out of the box. Stick a 90 db tweeter in the same spot and you will notice the 16 db difference! As Haemphyst said, "More woofers, or more efficient woofers... ( ported box) that's all you can do, man.

If you are looking at DB Drag you need to lok into the rules close, there is no limit on power. If you are looking at the USACi side of competitions then you have issues beacuse there is no class that ends at 500 watts If you are looking at another orignazation please list which one so I can make better suggestions. In USACi you can use 301-900WRMS at 4 ohm to fit your 500 watt system in DB drag you would be in Street A which would entitle you to 1 12 or 2 10's with up to 2 strappable d class amps.2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR

2007 USACI World Champion

2007 World Record

2006 USACI Finals 2nd Place

Thanks for all your help, the reason I was trying to stay in the 500 watt range is because the guy at one of the local stereo shops said that for the db drag they had the smallest class went to 500 watts, but if the 900 watts is correct I am screwed against the competition.  Do you have a link for the rules in DB Drag in Nor Cal.  If that's the case I think I might add another 300 watt amp, but then would also need to add a sub, my whole install was made to keep most of my hatch empty, If I install another 12 then that won't help, what about 600 watts to 1 12"  would that get me more volume or just be an easier way to blow up my sub???  And what does externally bridged amps mean, two seperate amps?