Extending the life of a connecting rod involves matters both sophisticated and simple.
The sophisticated—use of proprietary steels and high-tech treatment processes—provide a foundation, but they only work if more simple ideals—cleanliness of the build and proper lubing, for example—are used.
Indeed, it all plays a role in the long life of a connecting rod, according to Steve Arent from Scat in Oxnard, California. "Extending the life of a connecting rod will only happen if correct rods are used in the build," he said, "and correct procedures are followed."
Our sources dove deep into the specifics of the sophisticated and simple for this look at rod longevity. We'll start with perhaps the No. 1 topic: using the correct rod.
THE APPLICATION QUESTION
Roger Friedman at Dyer's Top Rods in Forrest, Illinois, said a common engine building question—"how do you know you have the correct rod?"—might, frankly, have more than one correct answer.
"I have some customers who run a certain weight rod. I have another customer who runs heavier rods. And then I've got another customer who runs lighter rods," he said. "They've all had equal success" with similar applications.
The difference for each customer is determined by asking questions about the overall build. "A lot of it has to do with the weight of your crankshaft, the weight of your piston, the weight of your pin, and then you give a recommendation," Friedman said.
One recommendation he makes is to use aluminum rods in power-adder applications. "The aluminum rod is a shock absorber; it will absorb detonation," he said. "The perfect example is the Top Fuel car. That freakin' motor all the way down the strip is detonating, and those aluminum rods survive."
He said super-high-performance engines like those in dirt sprint cars and Late Models suffer material fatigue from heat, rpm, and detonation.
"The guys who have the best success…they'll probably keep the crankshaft in them, but they'll change the rods after about three or four rebuilds," Friedman added.
Tom Molnar of Molnar Technologies, Kentwood, Michigan, has studied why connecting rods break, and it starts with rod selection. "I think the primary way to extend the life of a connecting rod is by making sure the correct rods are used for the application," he said.
Molnar, too, recommended "connecting" with those building an engine or supplying the parts. "Our sales staff spend a major part of the day helping our customers with their rod and crank selection," he said.
A key to longevity is matching a rod to horsepower requirements, said Kirk Peters from Howards Cams, Oshkosh, Wisconsin. "When using power adders, boost, or nitrous, a balance needs to be in place between weight and desired horsepower."
You won't be surprised, however, by this caveat: "In the end it's about the dollars a racer has to spend on his parts," Peters added.
Richard Batchelor of CP-Carrillo in Irvine, California, said choosing the right rod starts with what power level the customer needs and for how long—drag racing vs. endurance racing, for example. Bore, stroke, horsepower, where that horsepower is made, maximum rpm, and piston assembly weight are additional variables.
He said customers sometimes see "light weight" and think they've found their rod. "And they just think because it's a Carrillo it's going to handle whatever they throw at it," he admitted. "Any rod manufacturer will tell you they design their rods for specific power levels and types of racing, not just all-out everything."
THE SOPHISTICATED
Those seeking more longevity from their rods might want an upgrade in material, such as the proprietary C107 high-strength steel alloy used by CP-Carrillo in its I-Beam and H-beam rods for drag, circle track, road racing, and other applications.
C107 weighs the same as the 4330 steel used in other CP-Carrillo rods but is about 22% stronger. With that, CP-Carrillo can reduce cross-sectional areas and make the C107 rods up to 16% lighter.
Sometimes, however, less cross-sectional area is removed to "get more life" out of the rod, Batchelor said.
Such is the case for a circle track engine builder who was having some problems with connecting rods. "We did some testing with him first [with C107], and he liked what he saw," Batchelor said. "He's changed his entire program to this material."
The customer chose an option where he saved about 10% to 15% in weight—not quite the maximum 16. "He wanted a little safety in there, so we left it a little heavier," he said. "That was for longevity."
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