Well you did say you wanted it loud! That is as loud as it will get.
Are you confusing volume with horsepower? I attend a lot of national meets and am very familiar with top fuel cars. They are loud enough to vibrate all of the water out of an uncapped bottle just from the noise they make as they drive by down at the track. The noise they make isn't generating power (just the opposite is true; in that nose is defined as power being lost by an engineer).
I run flowmasters on my car. But I choose the biggest case (70 series) that I can stuff under the car to muffle down the noise my engine makes. The first time I cranked my car up uncapped, in my steel shop building, the fluorescent light bulbs vibrated out of the sockets as I was adjusting the timing; dropping all around me and leaving me in the dark. That was an expensive illustration of how much power is lost to noise.