There are plenty of fixed components in an engine that are moved by other parts yet play an important role in the combustion process. A good example of this is connecting rods or conrods as they’re also known. They are the important link between the piston and the crankshaft.
Be it cast or forged, conrods help the force generated in the combustion chamber get transferred from the piston to the crankshaft. Also when you start the engine, the crankshaft is the one that moves first and the conrods here help the force from the crankshaft to the piston to be transferred. But like engines themselves, there are different types of conrods.
Types
I-Beam
An I-beam engine piston rod is one that if you were to dissect it you would see that inside it resembles the letter “I”, hence the name. They are the most commonly used con rods as most manufacturers use them for their low cost and their durability in today’s engines. Although heavier than an H-beam con rod, an I-beam piston con rod is far more versatile as it can sustain more than 1,000 HP if made from the right material.
H-Beam
As you’d expect an H-beam conrod would look like the letter “H” if you were to see its cross-section. Their shape isn’t just for show though as they are made to be used in engines that generate a lot of HP at low speeds and somewhat lower RPM than what a naturally aspirated engine does. These are typically found in turbocharged and supercharged engines since they generate power a lot quicker and lower in the rev range than their non-turbocharged counterparts.
X-Beam
With an X-beam engine piston rod, you can expect to get the best of both worlds but do not expect to get a solution that will excel in both camps. Cross beam conrods as they’re also known are a hybrid design that are able to handle tension across its entire surface without weighing a ton. They are made for racing applications.
Conrod Materials
Aluminium
Talking about racing, if you want to maximise the power you get from high revs and shorten the amount of time needed to get to that part of the RPM range then consider going for aluminium connecting rods. They are quite light but also quite strong and because of their construction, aluminium conrods act much like shock absorbers when it comes to high-powered engines.
Steel
Steel conrods are the industry standard as they’ve been the go-to option for many manufacturers since the 60s. Steel comes in various grades which is why it can be used in almost every application. Keep in mind though that, steel conrods are much heavier than aluminium ones and despite being stronger they are not ideal in engines with a wide RPM range.
Titanium
One of the best materials for conrods when it comes to doing it all is titanium. Titanium conrods are the most expensive option but they are lighter than aluminium ones and as strong as steel conrods. But titanium conrods are not suited for everyday driving as that would be overkill, however, they are more common in drag cars.
Important Factors
Rod Ratio
A conrod’s ratio is its length divided by the stroke of the crankshaft. Rod ratio affects multiple factors such as the efficiency of the engine as well as power and torque. With the correct rod ratio you can also reduce the amount of wear on the piston.
Rod Length
The length of a piston con rod affects the ratio of a rod and everything else. This means that a shorter conrod is much better suited in engines that operate at their best at lower RPM. Longer connecting rods are better in high-revving engines as the ratio they provide allows you to get to the higher RPM powerband much easier.
HP vs RPM
Both horsepower and revolutions per minute matter in an engine but depending on the type of engine your car has and the type of driving you need to do you’ll always favour one. In high-compression engines and those with more than 4 cylinders, you will have to go for conrods that go in favour of HP rather than RPM.
Of course, this depends on the total RPM range as well as the powerband in which the engine creates the most amount of power. When it comes to engines that creates a lot of torque you should take a look at conrods that can sustain more pressure but keep in mind that these will be heavier and thus won’t be good enough when it comes to getting the highest number of HP from your power plant.
Conclusion
Despite not being seen doing their thing, conrods are one of the most fundamental engine components as they provide support to other equally important parts. They don’t have to be the best of the best, as long as your conrods provide what your engine needs you will have a long-running engine and a powerful one.
Australian Guru 