I seriously doubt you will make any extra power. The car is programmed to take advantage of backpressure from the factory cats to aid in exhaust gas recirculation for lower emissions. Without programming the ECU to take advantage of the lower backpressure, your car will not make more power becuase the ECU will not "know" what to do with the additional flow. The result is that you will not make more power in absolute terms, but you will move around the powerband.

I also want to correct an urban legend about BMW cats. Have you seen the factory cats on an M60 powered car? They are very large. And they are not that restrictive. The real problems you have with restrictive cats are generally the aftermarket crap, which is too small and causes performance issues. The other biggest problem you see is people comparing performance with factory cats are at the end of their lifespan versus no cats. Even here, the reality is the engine is merely back up to peak output, albeit with a modified power curve reflecting the lack of backpressure.

I am not saying you can't make more power through modifying the engine. But on a car as thoroughly engineered as a BMW, there's not much "low hanging fruit" so to speak. So just pulling the cats, by itself, and without doing other things, like reprogramming the ECU for starters, is not likely to give you real gains in performance as compared to the same motor with functioning, original equipment converters.

• New twist to 'green' motors, requires a question: - e34jef 2008-05-16 19:16:48 (146 views)
  • No cat update: - e34jef 2008-05-21 08:01:02 (105 views)
    • Without an ECU Update . . . . - rlomba8204 2008-05-30 16:01:11 (50 views)
      • No EGR, at least not in my particular car - dave535i 2008-06-01 09:43:03 (49 views)
        • Internal EGR - kfister 2008-06-01 20:25:30 (45 views)
    • Wow - kfister 2008-05-21 09:45:14 (69 views)
      • Wolf and a Dinan in the ATrans ECU. (nt) - e34jef 2008-05-21 17:32:41 (79 views)
        • BTW Ken ..... - e34jef 2008-05-21 17:43:30 (77 views)
          • I actually bought a CO-alarm from the home warehouse for the garage - kfister 2008-05-23 07:52:27 (70 views)
  • Might not be worth it.. Also your OE cats are worth much more - kfister 2008-05-17 15:42:28 (86 views)
  • HA! No Emissions...I live in California!! 76 down..are exempt (nt) - louiseven 2008-05-16 23:30:07 (77 views)
  • Re: New twist to 'green' motors, requires a question: - yaofeng 2008-05-16 20:41:54 (86 views)
    • Re: New twist to 'green' motors, requires a question: - rick540 2008-05-18 07:19:15 (78 views)
      • i don't like either of them!! anyway(well maybe a range rover sport) (nt) - explodingbudgie 2008-05-22 02:28:27 (63 views)
        • Exact opposite for emissions in California!!! - spyjunior 2008-05-29 19:56:25 (50 views)