The 325i uses Bosch 0 280 150 715 injectors, which have a rating of 149cc/min, or 14.6 lbs @ 43.5 psi(3.0 bar)
The the M30 engine in the 535i uses Bosch 0 280 150 203 injectors which have a rating of 185cc/min or 17.6lb BUT at 36.25psi(2.5 bar).......so at the m20 b25 3.0 bar that is 19.30 lbs.
The m50 (green ) injectors do flow 17.5 lbs but at 3.5bar(50.7psi) so on the m20b25 3.0 bar they flow 16.2lbs.
I have never seen proof that the stock injectors are maxed out. Alpina got 210hp using stock AFM and injectors. Most people notice a difference after swapping injectors simply because they are replacing dirty injectors with clean ones.
The M30 AFM gave Dave a 4.6 HP increase with adjustable fuel pressure and dyno tuning. The majority of the people who try this mod get drivability problems. If you want to replace the AFM have a look at an MAF. The biggest restriction in the intake is the intake manifold, followed by the head.
The stock intake is a cold air intake and is well designed so you won't get any increase from adding a cone.
Sadly, the only easy/cheap hp increase for the M20 is a chip.
Last edited by Curtis; 09-12-2006 at 10:12 PM.