Types of V8s

Discussion in 'Technical' started by Pimpmobile Caddy, Sep 7, 2004.

  1. I've read pages on flat-plane and cross-plane V8s, but I've never understood the difference.

    Can anybody easily explain the difference between the two?
     
  2. #2 V8Vantage, Sep 7, 2004
    Last edited by a moderator: Apr 25, 2016
    On a flat plane crank, if you look down the length of the crank shaft it appears flat (it's is is one plane).
    On a cross plane crank the point at which the con-rods meet the crank are not all in the same plane, hance cross-plane crank.

    Look here: http://autozine.kyul.net/technical_school/engine/smooth4.htm
     
  3. Sorry, but I barely get it.

    But I'm guessing, is cross-plane crank the picture on the right and the flat-plane crank the picture on the left on those pictures above where it says "Flat-plane V8 for high performance cars"?
     
  4. The first pic, top left shows a flat plane and a cross plane side by side, it's not a great drawing but it's suposed to be in 3D.

    If you imagine a compass face, looking down the length of the cross plane crank in that first drawing, 1 is at North, 2 is at East, 3 is at West and 4 is ast South. On the flat plane crank, 1 is at North, 2 is at South, 3 is also at South and 4 is at North.


    The section titled 'Cross-plane V8' shows the end on view of a crank shaft (looking down the engine, the 'Y' shape is the cylinders above the crank). Notice how it looks like an 'X' - the crank has 2 'planes' 90 degrees to each other.

    The section titled 'Flat-plane V8 for high performance cars' shows an end on view of a flat plane crank, notice how it looks 'flat' end on, only one plane.

     
  5. #5 V8Vantage, Sep 7, 2004
    Last edited by a moderator: Apr 25, 2016
    There is a 3D rendered drawing of flat plane vs cross plane on this site that might be easier to understand.

    http://www.e31.net/engines_e.html

    Scroll down to V8 engines.
     
  6. If you look down the length of the crank from the front, one will look like this '-', the other will look like this '+'.
     
  7. wouldnt flat planes cranks have less Torque but be able to rev higher?
     
  8. they'd have less smooth power delivery and rev higher because of decreased rotating weight
     
  9. Now I get it.

    But cross-planes need balancers, right?
     
  10. A flat plane crank also gives a better exhaust tuning, increasing the power a few percent by increaseing volumetric efficiency.
     

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