This is a new GM Performance Parts big-block Chevy rod manufactured from 4340 steel. The process begins with a steel forging that is then CNC machined. Each connecting rod is heat-treated, stress-relieved, shot- peened, and Magnaflux inspected.
There are quite a number of parts inside a modified engine that provide fair warning before they’ve had enough fun. Connecting rods, however, are humorless. Connecting rods don’t malfunction. When a connecting rod decides to punch the pay clock, it usually takes a few of its workmates with it, and in many cases, those bits take the shortest possible route via an immediate escape hatch in the side of the block. Ka-Ching. Expensive.
 On the big end, the new rat-motor rod has a cap screw connecting rod bolt arrangement where the bolt threads directly into the connecting rod body. In comparison (as you're probably well aware), many passenger car connecting rods incorporate a rod bolt with a dedicated nut where the rod bolt is pressed into the rod body and the cap is fastened by a nut. |
No doubt, connecting rods are the vital link in your engine’s chain. One (big) way to ensure that a connecting rod won’t check out early is to consider the maintenance it requires. There’s a good chance that the typical engine-building practices for installing steel connecting rods may contribute to their early demise. GM Performance Parts has considered these factors, and much of their research may surprise you (in fact, some of this research may be absolutely contrary to what you once believed to be steel-connecting rod gospel).
Containing The Chaos...
There’s controlled chaos inside an engine and the connecting rods are in there to hold everything in check. As horsepower potential increases, so do internal forces, particularly those imposed upon the load-bearing components. GM Performance Parts reminds us that Mr. Newton's laws still have effect upon an engine. If there is something in the range of 18,000 pounds of pressure attempting to lift the cylinder head off the block, then there must be 18,000 pounds of force trying to blow the crankshaft out the bottom of the block. Consider the 18,000 pounds of force imparted to the crankshaft every time it rotates. The connecting rod caps experience "ovulation" as the crankshaft accelerates through it's arc and changes the load direction.
Bear in mind the pressure scenario for a second. What really keeps the engine together? In truth, it's just a bunch of rod bolts, and in the end, rod bolts are nothing more than a series of spiral wedges designed to create enormous forces (which in turn, counteract the forces trying to dump the crank out the bottom of the block). Of course, precisely designed and manufactured fasteners are more than lumps of steel with threads on one end and a hex head on the other. GMPP points out that selecting the right bolt and installing it correctly is a primary factor in obtaining maximum service from your connecting rods.
The installation of the fastener is a primary factor in connecting rod longevity, but unfortunately, there's quite a bit of controversy and misinformation out there when it comes to hardware. There are those who believe a correctly tightened fastener requires the application of enormous amounts of torque in order to keep the bolt from loosening. That may have been true years ago, but bolts and studs that were acceptable yesterday might not be quite so viable today. For a powerplant to stay intact, the fasteners must provide repeatable clamping forces that are greater than the loads acting upon them. So far so good, but how do you really know when the clamping loads are enough?