I used the 2.25" X-Pipe on my 4.4 - not sure if you need to go up a size for the 4.8 or not. The X-Pipe also offers a big of needed back pressure over what a straight pipe would give you, and as ekaz says, I think it helps smooth it out a bit too.

BTW - I CAN hear just a very slight bit of popping and burbling, but only when the engine is cold and when I decelerating from about 30mph. It is very slight and most people probably wouldn't even notice. I actually like that sound and wish it did it just a bit more!

Nice little mod - go for it!

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'08 335i Coupe - Barbera Red / Saddle Leather / Light Poplar Wood / 6spd Manual
Options: Sport, Premium, Cold Weather, Comfort Access, Active Steering (awesome!), Power Rear Shade, IPod Adapter, Navigation w/IDrive
Mods: M6 Wheels, Split Armrest, M-Steering Wheel, Euro Light Switch w/Rear Fog Lights, Short Shift Knob w/Matching E-Brake Handle, Clear Reflectors, CDV, Clear Bra

Retired:'04 X5 4.4i