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I-beam or H-beam

Discussion in 'Engine Building' started by the_crazy_russian, Jan 14, 2005.

  1. the_crazy_russian

    the_crazy_russian Junior Member

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    hi,
    building up my b18b for boost and am looking a purchasing some forged rods. I've seen and read about h-beams before, but haven't read much on I-beams. what's the difference between the two? is one better then the other?if so why? thanks for your time,
    B
    :worthy:
     
  2. MikeBergy

    MikeBergy Blah blah blah....

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    If you look at it from a statics POV, the I-beam can handle more bending stress in its rotating plane. In other words, you are probably less like to snap a rod from high torque loads on the power stroke. The h-beam has the advantage of a lower rotational MOI, so you can accellerate it faster. I personally wouldn't worry about the differences unless you are building F-1 engines, because most production rods are WAY over-engineered, and differences between two comparable rods is minimal, probably negligible. Styleteg, Cal (Mr. ME degree), pls chime in with any yays or nays.
     
  3. K2e2vin

    K2e2vin Senior Member

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    from what ive seen, most manufacturers sell the i-beams for lower torque purposes(like all motor, low boost, etc.), and h-beam for the higher output setups. i dont know why though.
     
  4. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    That's generally true. The I beams aren't as strong, but they have less material in them so they're lower mass and allow you to rev up faster. The H beams are stronger, but they're heavier too. That's more suited to FI applications, but unless you're going with some crazy power numbers, the I beam is fine.
     
  5. jamesA

    jamesA Well known pissed off telephone guy VIP

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    Thanks Cal, and to the thread starter. I'm gonna run with some IB Spec I beams myself. :)
     
  6. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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  7. Johnnylawless

    Johnnylawless Senior Member

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    Jeff (IB) put I-Beams in mine Knowing I was FI And looking to put stupid amounts of boost on the motor, so I'm pretty Confident in the motor build.
    He told me the rods and pistons were good to about 700HP. :blink:
     
  8. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    Sounds about right to me. :)
     
  9. brian11to1

    brian11to1 Senior Member

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  10. the_crazy_russian

    the_crazy_russian Junior Member

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    cool thanks for the great info guys, it was supper helpful!
    B :)
     
  11. MikeBergy

    MikeBergy Blah blah blah....

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    Not to add to the argument, since it really doesn't matter :p , but why would building builders use I-beams in their skyscrapers and crap if the H beam could hold up better under excessive loads. Mike before you post a rebuttal, do a couple of bending stress calcs, one for the I beam and one for the H beam. If "sigma" = MC/I , I=bh^3 with h in the vertical direction in your computer screen analysis. The I beam will have a much larger I (ie "Second moment of area", or moi) than the H beam, yeilding a lower "sigma" for identical bending loads. That higher moi will all be the I beams down fall when it comes to revving. Not being a smart ass, afterall I haven't finished school yet; I'm just questioning your reasoning. :p
     
  12. K2e2vin

    K2e2vin Senior Member

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    in buildings how do you know the difference between a H-beam and I-beam? wouldnt they look the same?
     
  13. MikeBergy

    MikeBergy Blah blah blah....

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    It's not that they are different geometrically, it's in the way they carry the load. Static engineering mechanics is fun!!!
     
  14. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    I don't wanna pull out the statics book from the garage right now. :)

    One laymans' argument for the I beams in construction is because they actually have a surface to mount shit on- you can do that with the H. :)

    I did finish school a while back, but you're still taking the classes and I haven't touched that crap in years- so you're probably right. :) :) :)
     
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