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Video: H-Beam vs. I-Beam Connecting Rods

What are the differences between I-beam and H-beam connecting rods? Learn why lighter-weight I-beam rods are perfect for high-rpm applications and why heavier H-beam rods are better suited for high-horsepower, higher-torque applications. Learn what separates aluminum, steel, billet, and titanium connecting rods, and much more!

     “One of the most common questions we get about connecting rods is what the difference between H beam and I beam rods is, and on top of that, what are the advantages of each. So first let’s start by taking a look at an example of each type of connecting rod. Here we have a typical I beam connecting rod. As you can see, it has a sort of concave side that runs the length of the rod and has raised edges. And if you were to cut that in half you would essentially have what looks like the letter I.

      Over here, we have your typical H beam connecting rod, and you can see these have larger flat sides that run the length of the rod and then there is a smaller center section that connects the two flat sides . If you were to cut that in half you would have would essentially be or at least look like the letter H.

      So what are the advantages of each type of rod? Well, first of all you have to understand that the configuration of the beam is just one part of the equation. You also have to factor in things like rod material, length and finish. Well, with all these things being equal, typically an I beam connecting rod is going to be lighter in weight. Although I beam connecting rods are typically used on stock applications, the lighter weight also makes them desirable for higher revving, higher RPM applications where you want less weight in the reciprocating assembly. Conversely, H beam connecting rods are a little bit stiffer and rigid and that makes them ideal for higher horsepower, higher torque applications where there is going to be more compressive forces again this comparison only holds true if your comparing rods with the same material, finish, and length.

     So I mentioned that choosing the right rod material plays a huge part in selecting the proper connecting rods for your application. So I kind of want to take a look now at some of the materials we have available. In particular, we are going to look at aluminum, steel, billet, and titanium rods. Starting with aluminum rods, these are obviously a very light weight alternative to choose and they’re great for high RPM, high revving applications because of that light weight; however, they are a little bit more prone to stretching and fatigue than steel connecting rods. While steel connecting rods wont stretch or fatigue as easily, there is a weight factor involved when you choose steel connecting rods–they’re going to be heavier than the aluminum rods and that makes them less desirable if you’re running a higher RPM application. On the top end of the spectrum, we have billet and titanium rods. They offer the best of both worlds really. They have a light weight and are also extremely strong; however, you’re going to run into budget concerns when choosing those types of rods. They definitely run on the higher end of the price spectrum.

     Now I want to go back and talk a little more about steel connecting rods because there are a lot of different types of steel available, whether you are talking about manufacturer process or the actual material used. So let’s look at a couple of the manufacturing processes first. You have cast and forged connecting rods. On a cast connecting rod, essentially they take molten steel and pour it in a mold and cool it down quickly and that becomes a cast connecting rod. With a forged connecting rod, you are taking essentially a single piece of metal and you are actually stamping the connecting rod out of that piece and a forged connecting rod is typically much stronger than a cast connecting rod. And a cast connecting rod is typically a little more brittle than the forged style. Cast connecting rods are typically ample for stock or mildly modified applications whereas a forged connecting rod can handle a little more modification a little bit more horsepower and torque. We also get a lot of questions regarding the numbers you often see with steel connecting rods or steel components in general. You may see a 51 40 steel or a 4340 steel–people want to know what do these numbers really mean. They just generally refer to the tensile strength of the steel. For example a 5140 connecting rod is ready to handle about 115,000 PSI whereas a 43 40 connecting rod can handle upwards of 145,00 PSI and that is why you often hear about the 43 40 material referred to as aircraft grade.

     So with all of the different connecting rod configurations and materials available how do you know which one is right for your application. Well there are a few things you’re going to need to consider including the intended purpose of your vehicle–whether it’s a street or race vehicle–how many maximum RPMs you plan on running, horsepower or torque level, and even your budget. So let’s start by taking a look at a stock or mildly modified street application. In this case, a good set of cast or forged I beam connecting rods will likely do the trick; however, if you’re really going to start stepping up the modifications and start going with higher horsepower numbers, you’re going to want to consider stepping up to a set of good forged connecting rods for sure and may even want to look at a set of H beam connecting rods because again this type of connecting rod is a little more rigid and stiff and can handle the higher compressive forces generated by the higher horsepower and torque. For race applications or any higher RPM applications, you’re going to want to look at any way you can to reduce weight on your connecting rods . Consequently, you’re going to want to consider I beam type connecting rods. As I mentioned earlier, this type of connecting rod is typically a lighter weight than an H beam connecting rod. You are also going to want to look at lighter weight materials such as aluminum, billet, or titanium. Again, you are going to be limited here by what your budget is.

     Obviously if you have any type of questions regarding what connecting rod you’re going to need for your application a Summit Racing Tech rep would be more than willing to help you out. Now if you have further questions about connecting rods or any other high performance related topic, feel free to leave a question in the comment section below.”

 

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5 Comments

  1. Pingback: H beam vs I beam rods,........... - Ford Mustang Forums : Corral.net Mustang Forum

  2. Thermal stresses or effect of change in temperature i.e. (change in yield strength) should be taken in consideration for material selection.?

  3. Stanley Farirai Katsande says:

    how do I calculate the compression strength as well as the bending moment of an I beam?

    • OnAllCylinders says:

      When getting into applications where compression strength and bending moment come into play, we’d recommend talking directly with connecting rod manufacturers like Eagle or Manley. We’d also recommend a look at this article: http://www.enginebuildermag.com/2008/09/connecting-rods-so-many-choices/. The key takeaway is this: “Higher power levels increase the compressive force on the connecting rods while higher rpms increase the tensile strain on the rods. As it turns out, most rods don’t bend and fail on the compression stroke but are pulled apart at high rpm and break on the exhaust stroke. Consequently, rods need additional compression strength and stiffness to handle higher horsepower loads. But in hig- revving engines, increased tensile strength is an absolute must for the rods to survive at high rpm.”

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