Ouch, firing up? bummer. I was wondering how you got them in there. The AC trick is to keep the air dense, colder air is more dense and can yield you more dB (not much, if any but the judges will appreciate the cold car while they place the mics..LOL). Also using your AC may cause your voltage to drop below its normal range after a long period of time. Did you say your is car off while competing?? Then you are loosing voltage right off the bat. When your car is running it should be at 14V or more, with it off is will be about 12.8V. I would recommend you keep the car running. Also another trick is to keep sunlight out of car, Light absorbs sound (seriously) if you have tint then you are already good to go.
I dont think you will be able to port that enclosure you have so lets play with the note you play. I would guess that you may be better off in the 60HZ range, most common is 61-63hz at dB drag events. what ou need to do is play a sweep from 45-65hz at a low volume with a meter in your car at the dash. find the peak frequency (48 may seem the loudest to your ears from all the air it moves but I will bet that you will be louder at a higher note) Once you establish the peak note, play that at full level and you should see a major improvement.
