Power Acoustik equipment

I recently purchased a some Power Acoustik equipment consisting of a MOFO 15, 1800 Watt Class D amp, and 2-1.2 Farad capacitors.  The sub is in a 3.0 cu. ft. custom ported enclosure tuned a 45hz, the sub is facing the rear and the port is blowing out the front into the cab.  This is my delima, when the trunk lid is closed bass output is much less than if it were open.  Why is this?  I just competed in my first SPL contest and was very disappointed with only 132.9 db between 52 and 55 hz.  Is this a result from poor enclosure design or the equipment?   The rules would not allow me to make a pass withthe trunk lid open, so I'm not sure what the difference is, but quite noticable.  Any help would be great because at this point I'm ready to sell it all and start over.

Have you tried facing the sub towards you instead. I notice this with my sub in my suburban also. When I open the back door I definitely can notice more bass output from the drivers seat. If possible in your vehicle try facing the sub towards you. Experiment with other locations also.

The box I have now is custom fit so there is no way to try different placement.  I previously had two 10" Audiobahns in a sealed enclosure and I tried different placement, however facing to the rear was best for them.  thanks

If you have your driver and your port facing in opposite directions, then yes, you have created a cancellation effect.  This is the worst possible configuration.

Sound waves are like surface waves in water.  They go up and down and have a set distance between the peaks.  A 50Hz sound wave is approximately 22.5 feet long.  So to achieve maximum SPL at this frequency, the sub needs to be 22.5 feet from the listening point.  That is why facing a sub towards the back of the car tends to create more SPL in the drivers seat: you have increased the distance the sound must travel by making it bounce off the back of the trunk before it gets to you. 

When you face the sub one direction and the port in another direction, you have now created two paths for the sound, and the waves will arrive at different times.  So what I suspect you have done is created a situation where the waves between 52 and 55 Hz (which will be about 22 to 20 feet long) are arriving from the port before the other set arrives from the sub cone, and one is cancelling the other (because the peaks hit at different times.)

Does this make sense?  This is why the best subwoofer system designs always have the port on the same side (baffle) as the drivers.