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Thread: Why the cookie cutters in megaphones?

  1. #1

    Why the cookie cutters in megaphones?

    What's the reason for the cookie cutter inserts in the megaphone ends on early 911 race cars?

    They look cool and unique but not sure how they help?

  2. #2

    Great question

    I've often wondered that myself. The inserts would seem to be too remote from the heads and headers to have any beneficial effect on the flow of the exhaust gases. Perhaps they're meant to support the megaphones so the shape isn't distorted by heat. Just a guess.

    1972 911S- viper green
    1970 914/6- tangerine
    1967 Ferrari 330GTC- oro chiaro

  3. #3
    Everyone asks the same question about my "Competizione Riservata" mufflers on my Guzzis. Except in my case they want to know if the exhaust propellers "spin" when the motor is running.
    I tell them to follow me closely and see for themselves.
    I suspect it is a scavenging device that creates some sort of "vortex". Any PE's, ME's or AstroPhysicists here?

  4. #4
    Some thoughts from the other board......

    I think that there are more to them than the cookie cutters you see in the end of the megaphone. I think that they are some sort of flow splitters. I read about them somewhere in regards to something called the "coaenda effect". (I don't spell well)

    Some of you motorcycle guys probably know about this. It had an extraction effect at certain velocities. This would determine the size and shape of the exhaust.

    Thats all I remember about it.

    Good luck,
    David Duffield

    Junior Member

    Registered: Mar 2002
    Location: Ann Arbor, MI
    Posts: 22
    It's the coanda effect and you are correct. It creates a scavaging effect inside the megaphone (less backpressure).

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