EXHAUST:
A CERTAIN AMOUNT OF BACK PRESSURE IS NECESSARY FOR PERFORMANCE-
If you had it "dynoed" without the packing it might work out, but you may loose H-P and ride-ability
FOR EXAMPLE:
I have a "muzzy" 4-1 stainless on a zx-11...
had it dynoed with the "muzzy" can, had a "big dip" in the power curve, got it out with a "jet tek" can.
Did not like the sound, but the performance was great.
Gutted the Muzzy to be a straight through can ...
ran it and the perfomrnace, ride-ability, gas mileage way off, it was "mucho loud"!
I have removed the "gutted" muzzy can in favor of the "Jet-Tek" can;
don't like the sound, but sure do like the "performance"
Good Luck