Okay since I'm going for becoming an Automotive engineer we have actually tested this and several other "cheap horsepower ideas". The whole air vortex or whatever doesn't actually work. It just caused turbulance. If you really think about it what does the spacer do???? it just makes the intake...
I had 2 memphis 15's in my sedan and it fit just fine. I built box to spec and tuned it for 40hz with only 600watts it hit 138.9dbs w/ back seats down. So Just make sure w/ l7's u have plenty of power and u'll easily be in the 140db range