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V-12 exhaust flow question

Discussion in 'Technical Q&A' started by snj5, Jan 14, 2007.

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  1. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    #1 snj5, Jan 14, 2007
    Last edited by a moderator: Sep 7, 2017
    As I am studying exhaust systems, I did a quick survey of some layouts of the early Ferrari V-12 systems (below). First of all, they are pretty substantial amount of metal. The pattern I noticed was the 3-2-1 header progression per side which then again spilt into two exhaust pipes before or in the first muffler follwed by two of the same size through the end, usually w/resonated tips.

    This is contrary to what I've been taught on keeping flow velocity high by keeping the same pipe diameter the entire way through. When the exhaust splits into the two, the amount of pipe cross sectional area seen by the exhaust flow goes way up.

    I am thinking that this may have been done for sound rather than flow. It's intersting that when you look at the system from a distance with those slant cut ends the exhaust system looks like organ pipes.

    Any comments on the effect on flow or sound by splitting into two paths after being in one pipe?

    Many thanks
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  2. t024484

    t024484 Karting

    Nov 9, 2006
    171
    Netherlands
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    Hans A. Polak
    #2 t024484, Jan 14, 2007
    Look here.

    http://www.geocities.com/motorcity/track/6992/vizard.html

    Although this article from Dave Vizard is discussing 8 cylinders, the same principles apply to 12 cylinders.
    If there is an expansion box somewhere after the pipes have joined (6-2-1), everything behind this expansion box does not influence the amount of HP and is not "seen" by the engine, under the condition that the pipes and mufflers behind the expansion box have at least the same or a greater effective diameter as the pipe ending in the expansion box.
    These pipes and mufflers can be selected then to produce the desired sound level.

    Also note that the length of the primary pipes is not very critical, neither is it critical to give them the same length, this contrary to general belief.
    The length of the part ending in the expansion box is much more critical, so is the volume of the expansion box.
    All pipes, mufflers and cat's will need to have a flow of approx 2.2 CFM per HP.
    A straight pipe wil give you 115CFM per sq.inch at 1.5 inch HG.

    For a 600 HP 12 cyl. engine, a set of 6 cylinders will produce 300HP.
    You will need pipes and mufflers flowing at least 300 * 2.2 = 660 CFM.
    This translates to 660/115= 5.7 sq. inch or a pipe of at least 2.7 Inch in diameter.

    About the primary pipes: 600 HP/12 = 50 HP per cylinder.
    50*2.2=110CFM.
    110/115= 1 Sq.inch
    1 sq. inch corresponds to 1.1 inch in diameter.
     
  3. Fritz Ficke

    Fritz Ficke Formula 3
    Rossa Subscribed

    Jan 3, 2006
    2,270
    Tucson, AZ.
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    Fritz Ficke
    #3 Fritz Ficke, Jan 14, 2007
    To24484, Thanks you really helped answer a lot of questions . I am thinking about my 400I's 8 mufflers and just want more sound and maybe a cat. Fritz
     

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