4.8is full pipes and mufflers paired with my stock 4.4i (N64) with resonator intact sounds slightly deeper, but not quite at the 4.8is throatiness. I wasn't expecting it to make a huge difference in sound or performance, but the slightly deeper growl was enough for my liking. Looks good too.

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2000 Z3 2.3 Steel Gray
2004 X5 4.4i Jet Black