Induction noise is what gives these bikes that deep growl at low RPM's. Also getting rid of the breadbox resonator under the bike is what's really going to give you the loudness you're after. With the resonator still in place, pretty much all slip-ons are going to sound the same since the cat and resonator is doing the majority of the muffling. You can get rid of the resonator with either header pipes, or a cat-delete mid pipe, though that requires cutting and possibly welding, which is why most people just buy the headers.
After you've done headers / cat-delete, then you can decide on the loudness based on the size of the slip-on pipe you buy. Large slip-ons are quieter than small ones. Same goes for single vs. dual exhaust, single is louder. A single tiny little Austin Racing is going to be much louder than dual Akra bazooka's.
Also, don't base exhaust sound off YouTube videos. You're really only judging the quality of the person's microphone, if anything. It's like trying to judge the picture quality of a TV by watching a YouTube review of it, it doesn't work like that...
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