Quote:
Originally Posted by LANDLORD
There is a certain amount of back pressure that is designed into any factory exhaust system. It helps with bottom end torque and gas mileage. Factory exhaust systems are calibrated to work within the engine design and specifications.
There is a reason for these exhaust valves, the M has two of them. Yes you can defeat them and yes you can replace the exhaust system. It may or may not affect the engine calibration. Only the design/test engineers know for sure.
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But some one said for turbo engines, there is no back pressure in the exhaust. Only the NA engine has the build up back pressure in the exhaust.
For my X6 35i, the valve was removed and there is where I realized the low end torque was "lost" and the gas mileage has a huge increased.