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Thread: How to remove the restrictors from a stock exhaust

  1. #1
    apriliaforum expert irie's Avatar
    Join Date
    Jul 2006
    Chichester, UK

    How to remove the restrictors from a stock exhaust

    This has been done before but I'll spell it out again.

    The stock exhaust uses about 32mm tubing with maybe 2mm walls (?). The flanges for both headers have been very well welded. A bit too well actually ...

    Assuming 2mm wall thickness the internal diameter is 28mm, radius is 14 mm. So the area of the exhaust is Pi x Radius squared = 3.142 x 14 x 14 = 615 sq. mm

    In my road bike exhaust the welds protuded internally by at least 2mm all round.

    Therefore the exhaust diameter there is 3.142 x 12 x 12 = 452 sq. mm

    The weld area is 452/615 x 100 = 73%, so there is effectively a 27% restrictor in the exhaust.

    Filing off these welds removes the 27% restrictors! Whoever welds the stock exhausts has welded all the way through so filing off the inside of the welds still leaves strong joints.

  2. #2
    apriliaforum expert king karl's Avatar
    Join Date
    Nov 2006
    Bradford, yeh baby
    fanks for that

  3. #3
    apriliaforum expert cal550b's Avatar
    Join Date
    Dec 2006
    North Yorkshire
    Quote Originally Posted by king karl View Post
    fanks for that
    i still have your world famous exhaust in unrestricted form,fook its loud

  4. #4

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