Building your performance engine can be a long and drawn out process, and connecting rods are arguably the single most important factor. If you are putting together an engine build for maximum horsepower, finding a strong connecting rod is vital. The common engine building mistake that amateur engine builders make is finding the biggest turbo, or largest charge of nitrous or strongest piston, when it’s really your rods that need the most attention.
Lose a piston land or ring, the damage to your engine is minimal. Have a connecting rod break at 6000 RPM and with 25 psi of boost rushing through your engine however, and there’s little chance of salvaging anything. Your rods or what’s left of them will exit your shortblock and could possibly wipe out your cylinder head and anything else.
Connecting rods and the right combination of rod bearings and pistons will ensure your performance engine lives a long life. When shopping for rods, make sure to overestimate your horsepower numbers so that you have the peace of mind on race day.
The next part of selecting your rods is the connecting rod length, and how to properly measure it in your engine configuration.
How to Measure Connecting Rod length
The length of your connecting rods plays a huge role in your engine compression, and how reliable it is throughout the RPM band. Rod length is refers to the distance between the centerline of the wrist pin bore ( where the piston connects ) to the centerline of the crank pin bore ( where the rod connects to the crankshaft )
Typically this measurement is made using a long-scale precision caliper, although you can use other measuring points to get the job done.
Determining rod length is easy to do with the right tools, by measuring from inside to inside of each of the bores, then adding one-half to each side of the respective bore’s diameter. This is the first of three measurements you’ll be using to determine rod length.
Use the inside edge of the caliper to measure from the bottom of the wrist pin ( piston end ) to the top of the crank bore. Remember you are measuring the points of the two bores that are closest together if you are confused.
Record this measurement and then using a bore gauge, measure the write pin bore and divide the diameter by 2. Now you’ve got two measurements to work with, let’s call them A, B and C respectively.
Now you’ve got to add these three figures together, A+B+C to determine your total connecting rod length.
Don’t forget that all you are really doing is adding the bore’s radius to the distance from the bottom of the wrist bore to the top of the crank bore. Many rod manufacturers do an excellent job of concise measurements and exacting figures, but when you are building the ultimate street rod, always do the measurements yourself to be sure.
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