Connecting rods
Connecting rods
The connecting rods are some of the most important components in your engine and the most crucial elements in engine tuning. Since they are exposed to extreme forces, they have to be able to sustain a lot when you boost your car’s performance.
In order for them to withstand the respective load, manufacturers vying against each other to attain better design and select better materials. That’s why there are very different types of connecting rods on the market. Each design has its advantages and disadvantages and is designed for a different application. There are also a few myths surrounding connecting rods. You will find out what types of connecting rods there are and what they are good for here.
What are conrods and what are they for?
Conrods or connecting rods are important and heavily stressed components in your engine. They sit between the piston and the crankshaft and convert the linear movement (up and down) of the pistons into the rotational movement of the crankshaft. In this process, high forces act on the conrods: from extreme heat to pressure and tensile and lateral forces. They are also subjected to bending and buckling. Stock conrods are not suitable for use in the tuning sector and can quickly break under the load. To prevent this from happening, high-performance conrods are designed from stronger materials and with a different cross-section than the stock models. This way you are on the safe side with your performance-enhanced engine and don't have to worry about major engine damage.
Structure of a connecting rod
The connecting rod consists of a rod shank that connects the small end (small eye) and the big end (large eye). The small end is mounted on the piston pin and the big end is mounted on the crankshaft. The rod shank itself can have different cross‑sections that define the respective type of connecting rod: for example I‑beam, X‑beam or H‑beam.
The big end is split for installation on the crankshaft and is mounted on the crankpin with a plain bearing. The small end houses the piston pin and is equipped with a small‑end bush. For optimum lubrication, an oil channel is usually drilled through the connecting rod to lubricate the pistons.
The type of split can also differ: there are straight‑split rods and angled‑split rods (the latter for example in diesel engines).
The separation processes are also variable: they can be cracked (fractured) or milled/ground. In cracking, the rods are first manufactured in one piece and then provided with a notch. They are then deliberately broken (cracked) at the intended fracture point. This type of separation enables particularly good force transmission, as rod and rod cap fit together exactly. So that they fit together precisely, the rod and rod cap must always be used together and cannot be replaced individually.
From which material are conrods manufactured?
Conrods are manufactured from different materials. Since they need to be very light on the one hand and very strong on the other, sintered metals and high-quality aluminum are particularly suitable. Aluminum conrods are very light and stable, but they do not last as long as steel conrods. Conrods are rarely made of titanium as well. Depending on the material, conrods are either forged, cast, or milled from solid material.
Which types of conrods are there?
I-beam conrods (I beam)
Which conrods for which engine?
In the past, the rule was: under excessive tensile load, conrods can easily crack because this force is linear. How strong a conrod is under tension depends primarily on its cross-section and the material. In boosted engines, where compressive forces act on the conrods, things are different. Here the conrods bend because these forces are not linear. The shape of the conrod plays a greater role here: an H-beam conrod is lighter than its I-beam counterpart and can better minimize these forces. So, with lower weight, it is more stable against compressive forces and is therefore more suitable for boosted engines.
In the meantime, we are able to manufacture conrods with different cross-sections and materials for all application scenarios. An H-beam conrod is therefore not necessarily better or worse than one with another shape. It mainly comes down to the design and the material.
Therefore, when choosing your conrods, you should pay attention to the power they are designed for. Also look at the material and do not use low-quality conrods. These can crack or bend too quickly, which will ruin your entire engine.
Conclusion
In the past, the shape of a conrod played a much bigger role than it does today. Nowadays, it is crucial what material a conrod is made of and how it was designed. In any case, you should always rely only on genuine quality conrods in order not to damage your engine. This applies especially when increasing performance.
Optimal accesories for the conrods
