but a WWII fighter plan loud. .
You actually have to use packing.
True that, unless you run WFO throttle all the time (...unlikely.)
I had a 4-1 V&H pipe on my CBR1000F, after about 5 years not only was it obnoxiously loud with a terrible exhaust note, performance wasn't as good as I remembered. I pulled the baffle only to find about 75% of the 'glass was gone. I repacked it and was astounded at the difference, not only in sound, but performance.