that would be 10% saving gas, as for the power and tourq, it would increase about 5% in HP and 10% torqe, you could almost get your 4,4 to go as 4,6is.
Anyways with the gas price that we have in EU, and me driving 20.000/year it would take me 1½ year before i start making any money by having the chip

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X5 4,4i-06 Current
330Ci Cab-03 2007-2008
MB E55 AMG-03 2006-2007
Z3 2,8 Roadster-98 2006-2007
X3 2,0d-05 2005-2006
320d-99 1999-2005