There is a lot to consider when you choose the conrods for your engine—the type of engine you are building, the desired torque and horsepower curves the engine will produce, the maximum rpms it will turn, the physical dimensions of the engine itself and so on, but you cannot deny that the very quality of the products is what of your great concern.
The rods must be stout. Why I said so? Just imagine the little creature—rod, connected to piston and crankshaft, roll itself in the high-temperature cylinder and transit four tons or even more from the piston to the crankshaft, doing it hundreds of times per second at racing speeds. Hard to believe it! And this undoubtedly requires the conrods to be made from qualified materials with excellent techniques to ensure its quality.
As for the material, I suggest you take the ones made from forged SAE 4340 EN24 Chrome Moly Steel for the highest strength and durability. And ARP Bolts being used in conrods will be a better choice, for these very ARP Bolts are capable of achieving a clamp load at 220,000 psi and eliminating the problem of stress corrosion and hydrogen embrittlement, which means undoubtedly another ensurance for the strength and stiffness of the rods.
When it comes to the techniques, I recommend you to take the ones honed by SUNNEN machine, which provides precision bore size, surface finish, and even a non-directional surface texture which improves bearing life.
Choosing the right conrods is always important, and I hope the tips above can be of assistance. Good luck!