I've Heard the HKS system on a Z that had race pipes and it was loud. It doesn't sound raspy like a four banger but it doesn't sound smooth like the Nismo Unit and is a totally different sound. I think the test pipe may have made it louder and a little more raspy. It doesn't sound all that bad if your in to that full on drag racing sound, but as a daily driver...i'll pass. I got the Nismo Catback System and love it.First of all, I disagree that a Ti. exhaust sounds like a 4 banger. I invite any of you to have a listen, in person. And honestly tell me that what i've got resembles 4 cylinders.
Secondly, the HKS Carbon Ti., is not a true Ti. exhaust. So I doubt it will sound like a true Ti. version.
And just to throw this into the mix.. The ARC ti. that I have on the car was not raspy sounding at all. In fact, I hadn't obtained a hint of raspiness until I installed the RT cats and Strup headers.
Go and listen to the exhausts in question. Pick the one you like the most.
NISMO all the way, and remember, Nismo S tune parts do not void and warrenty on your engine....