Everyone knows about the M50 manifold mod for the M52 engines, but I think I may have found the same thing for the 5 series...
Basically, pre 09/1999 535i's (235bhp) use an old style intake manifold. These manifolds were also used on the E34 530!!! and other x35 models of the same era - so I'm guessing they're quite restrictive.
Later 535i's use a different manifold, used exclusively on the 535i and 540i models (although I'm guessing the older E34 540i - 4.0l). These newer models produce 10bhp more!
Has anyone else done any research into this mod? It looks as if this may be an easy mod for more power for 535i owners.