I-beam or H-beam

[the_crazy_russian]

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

 

[MikeBergy]

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.

 

[K2e2vin]

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.

 

[phunky.buddha]

Originally posted by MikeBergy+Jan 14 2005, 07:07 PM-->

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.

[post=445854]Quoted post[/post]​

Actually, it's the other way around... the H beam will resist bending in an engine more than the I beam- you have two vertical members resisting bending instead of one with the I beam:

Imagine H vs I sticking straight up out of your screen, both bending vertically- the H will resist bending more. The I will be stronger bending horizontally on your screen, but if you're experiencing stresses like that in your piston engine, you've got some major problems.

You're right though- the design doesn't matter much for your street built engines. IB has tested the I beam Probe Ultralites up past 600whp without any issues.

K2e2vin@Jan 14 2005, 10:01 PM
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.

[post=445902]Quoted post[/post]​

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.

 

[jamesA]

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

 

[phunky.buddha]

 

[Johnnylawless]

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.

 

[phunky.buddha]

Sounds about right to me.

 

[brian11to1]

I Beams for ME

 

[the_crazy_russian]

cool thanks for the great info guys, it was supper helpful!
B

 

[MikeBergy]

Originally posted by Calesta@Jan 15 2005, 12:10 PM
Actually, it's the other way around... the H beam will resist bending in an engine more than the I beam- you have two vertical members resisting bending instead of one with the I beam:

Imagine H vs I sticking straight up out of your screen, both bending vertically- the H will resist bending more. The I will be stronger bending horizontally on your screen, but if you're experiencing stresses like that in your piston engine, you've got some major problems.

Not to add to the argument, since it really doesn't matter , 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.

 

[K2e2vin]

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

 

[MikeBergy]

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

 

[phunky.buddha]

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.