675.cc • Triumph 675 Forum

Custom velocity stacks

Discussion in 'Other' started by panos_zip, Oct 9, 2016.

  1. panos_zip


    Thread Starter

    Location: Liverpool

    I decided to take my bike for new custom map so I was thinking to add stacks. I found a machine shop that can make them according to my needs for about 50 pounds
    I understand that the longer ones are for mid/low range and the short ones are for top end power. I have seen in this forum that many of you have combinations of lengths.

    So many questions arise
    What length or lengths?
    All short? All long? 2 shorts 1 long? 2 longs 1 short?
    If I chose different lengths, how should I place them?
    What could be the difference, if I place the shorter on the left instead of the right, for example?

    The bike is a 2009 used mostly on track days and occasionally on rides with other ss bikes.
    arrow full exhaust, KN filter, race ECU and loom, short gearing.
  2. Electric kid

    Electric kid

    Location: Sandhurst
    I'm not an expert in this, but do have a little experience with top end sports cars that have adjustable length inlet tracks.

    For me it would be all the same length, and if/when I put them on it will be all short for track work.

    I can't make sense if a mixture of short and long since it feels like it would result in an in balance from one cylinder to the next. A manufacture might use inlet tracks that are fractionally different in length to compensate for slight pressure difference.
  3. My understanding is that you would need to map the cylinders individually, I have the trumpet race stacks, two long one short but either need a race ECU to map it or get an alternate ECU to do the job properly, so haven't fitted mine yet
  4. panos_zip


    Thread Starter

    Location: Liverpool
    Both the stock and race ecu have different map for each cylinder but in order to map the individually you would need wideband lamda sensor to each one of the pipes of the header.
    Although that s the best way I think that it is a big hassle.

    From some google search, I see different curve designs and to be honest I m a little bit confused.
    I see very different velocity stacks between different bike models.

    About the length, I am still not sure. Triumph has two different options at the race kit, short and long.
    But without any further details about the exact length in mm.

    Probably, I will give one of the stock velocity stacks to the machine shop and I will ask them to copy the curve and make them shorter.

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