A local has a motordyne shockwave paired up with the ART pipes and it doesn't sound raspy at all. Loud and aggressive, yes. Raspy, no.
I think it's hit or miss with certain HFC/TP and exhaust combos.
F.I. site states this about their resonated HFCs:
Absolutely NO RASP from RPM idle to RPM redline in conjunction with our TDX cat back exhaust system.
Exactly why I'm considering picking a pair up in the future.
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F.I. / K&N / 180 / Forgestar 
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