How to Choose the Right Connecting Rods

Aftermarket connecting rods come in various designs, materials and lengths.
Picking the right combination will ultimately come down to these five key factors…
• Engine performance or output—as in horsepower, torque and rpm range
• Engine dimensions: this includes piston height and crankshaft stroke
• Application: street, drag race, endurance racing, etc.
• Piston weight
• Your budget
All of these factors will help determine the rod length, material and configuration that’s best for your application.

Let’s start with the physical design of the rods.

Stock I-beam connecting rods can handle upward of 400 horsepower and 6,500 rpm. Once you exceed those performance levels, you’ll need to consider aftermarket connecting rods. Depending on the type of material used, aftermarket I-beams can handle hefty compressive loads, offer good tensile strength and are often more lightweight than H-beams.

H-beam connecting rods use a completely different design to increase stiffness and strength.
They incorporate two large, flat sides with a thin section in the middle. This design makes these rods more rigid and able to handle compression forces; however, they are often more expensive. I-beam rods are easier to produce and can sometimes be lighter than H-beams. All other variables being equal, H-beam rods are the strongest design.

The three main materials used on connecting rods are steel, aluminum or titanium.

Most aftermarket steel connecting rods are made from forged steel. However, there are different types of forged steel based on the grade of material. Eagle Specialties, for example, uses a 5140 steel for its entry-level rods. For more highly modified competition applications, most manufacturers, including Eagle Specialties, utilize high-carbon 4340 or 4330 steel.

Aluminum rods can be as much as 25-percent lighter than steel rods, making them a popular choice with racers. The lighter weight reduces the overall mass of the reciprocating assembly, allowing the engine to rev faster and higher. The downside to aluminum rods is their fatigue life.

Titanium is a third option.

Titanium connecting rods combine the lighter weight of aluminum with strength that’s more comparable to steel. That makes them a viable option for drag cars or sprint cars that require quick throttle response. However, they are very expensive.

No talk about connecting rods is complete without determining rod length and rod ratio.
We'll get into those topics--and more--in our video!