Who has actually hollowed-out his primary cats? - BMW M5 Forum and M6 Forums

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Who has actually hollowed-out his primary cats? Who has actually hollowed-out his primary cats?
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Old 8th July 2009, 23:16   #1
PianoProdigy
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Who has actually hollowed-out his primary cats?
As stated, I'm looking for any and all feedback from those who have actually hollowed-out the primary cats. It seems that RPi has proved that the gains to be had (~30 hp/tq and substantial improvements in the midrange) are in the removal of the primary cats and not in a new header design entirely.

I'm particularly interested in those who are running a stock exhaust but for the hollowed-out primary cats.
Last edited by PianoProdigy; 8th July 2009 at 23:17.
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Old 9th July 2009, 00:58   #2
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+1 I want to hear about this as well. And how tough/time consuming of a job is it to do? I think I remember hearing Eloy say it was a real PITA, but I don't remember exactly.
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Old 9th July 2009, 01:22   #3
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Who is going to admit a felony..........???
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Old 9th July 2009, 05:04   #4
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Who is going to admit a felony..........???
Oh please...
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Old 12th July 2009, 00:01   #5
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If you remove the primary cats, will the stock secondary cats still allow it to pass the emmisions and even better has anyone ever done this and taken a reading from the exhaust.

In the UK I believe the car just has to pass the emissions test when it is 3 years old, which may be possible with just the secondary cats I'm going to keep my car for a little longer hence I'd like to get some data on just running the secondary cats.

Lastly does anyone do a secondary cat that definately passes the emissions?
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Old 12th July 2009, 23:58   #6
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Primary cats are only there for the cold start period. Emissions won't be an issue without them as long as you have the test done with a warm engine. In Germany they still pass the MOT without any problem.
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Old 13th July 2009, 00:38   #7
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Mike@AwdMotorSports has -> looking for an extra +50HP
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Old 13th July 2009, 01:21   #8
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Mike@AwdMotorSports has -> looking for an extra +50HP
What exactly is involved in gutting the cats, seems fairly straight forward? CEL safe? Hope Mike can chime in.
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Old 13th July 2009, 01:37   #9
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CEL safe?
Not CEL safe. You'll need software/tune to prevent that.
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Old 13th July 2009, 03:42   #10
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Interesting thread. Subscribed.
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