I suggest you start with everything from behind the exhaust manifolds and see how you like it. It's kind of a PITA to have to mess with the exhaust manifolds and starting there and working back would be quite a bit easier. If you still want to go through all that effort later to get 5 more horsepower into a pretty heavy ride you will be older and wiser already.

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2001 x5 3.0 (sold with broken motor), 1990 e30 M3, 1991 318is, 2002 325i, 2008 335i Dinan stage 3 6 speed,