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Message: <blockquote data-quote="fabianyee" data-source="post: 402014" data-attributes="member: 6">Tuning alone is not enuf, need to change the intake manifold too... Read somewhere that the 523i (M52B25) manifold has smaller runners compares to the E39 525i (M54B25) runners, improving low and mid range torque but restricts high rpm power..  M50tuB25 manifold has the biggest runners (compared to M52B25 and M52B28) which gives good high rpm power - can feed more air at high rev... But not so efficient at low rev bcos a big runner doesn't give low volume air the momentum it needed to 'charge' into the combustion chamber... Imagine 2 water hoses of different sizes, the smaller hose can spray water further compared to the bigger hose..</blockquote>