I just took off my 4.4i exhaust for 4.6is. earlier this week, I really like the look, there isn't a growl or anything. But It appears the piping is 2.5" vs 2.25" so maybe its exhaling a bit better, so maybe my truck is running a bit more efficient, on highways it seems to go a bit faster....but I love the chrome oval tip better personally vs the stainless steel quads. for $300 Its a good price, but its not an easy swap by any means, if you do it yourself, maybe 2 hrs, or pay shop $80-$100 to swap it out.

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2003 BMW E53 X5 4.4i - M62 engine (Non Sport with Premium and Cold Weather Package)
Color: Steel Gray Metallic
Mods:4.6is Exhaust (Pipes, Mufflers and chrome oval tips) BMW Sport package Taillamps, BMW Tire Valve Stem Caps
Medium tinted front windows
JVC HD Radio
Alpine 4x100 channel Amp
Orion 600W Mono HC Amp
Three 12" Sony Xplode in subwoofer enclosure