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Tech Review: Oliver Parabolic Beam Connecting Rods


By Jason Reiss

Photos Courtesy Oliver Racing Parts

It is physically one of the simplest parts contained within an engine, but one of the most important. The technology that goes into its manufacture must be decidedly precise. That’s because without it holding down its end of the bargain, you have no engine; instead you have a collection of parts that can’t perform their duties. We’re talking about the connecting rod, of course, because without the connecting rod, the crankshaft just spins in its bore, and the pistons don’t move. And that’s where Oliver Racing Parts offers a solution for high-powered combos — the Parabolic Beam connecting rod design that’s been manufactured at its Michigan facility since the 1980s.

“We find that for the higher-performance, high-horsepower applications, you get a better strength-to-weight ratio with our Parabolic Beam design. When you look at the cross-section of the beam, the distribution of the weight, and the strength of it, it’s a more robust design relative to the H-beam style connecting rod,” says Oliver’s CEO, Joe Moch.

“We have in-process air gauging for the big bore and the pin-head bore, and the accuracy of that gauging is to 40 millionths of an inch. It’s unique to do that in-process and on the shop floor, and every single rod we manufacture is run through that sizing exercise to maintain the accuracy of the bores. We’re holding that bore tolerance more tightly than anyone else out there as a result,” says Oliver’s Joe Moch.

Oliver creates just one product line — connecting rods. As such, a laser focus exists with the sole goal to create the best possible connecting rod money can buy — and the company has developed manufacturing methods to do exactly that. Every step of the process is controlled down the smallest variable, and material selection is paramount to performance.

With every part of an Oliver connecting rod sourced, machined, and boxed right here in the US of A, the team has complete control over everything from the raw materials to the boxes the connecting rods are shipped in.

“For us, it’s always been about controlling the quality of our product and relying on our suppliers to give us the best material possible. We work with a lot of the best engine builders in the country, and to know we’re getting clean, inclusion-free material is very important. We use a special grade of 4340 chrome-moly that’s designated AQ, for Aircraft Quality, which means it was vacuum-arc re-melted. The material is a cleaner grade of material through the processing that the mill does, with less risk of impurities in the material. That’s what distinguishes our rods from others in the market,” says Moch.

The fact that Oliver’s rods are manufactured — from raw materials to the finished product — right here in the US, with impeccable standards applied to the manufacturing process, means that the end-user can purchase with confidence. Everyone we’ve ever spoken to about Oliver’s connecting rods has raved about their quality.

Now, you might think that a connecting rod is a connecting rod is a connecting rod, but Moch assures us that’s not the case at all. Separating itself from other options also happens in the machining room with the company’s Geometric Dimensioning and Tolerancing control processing technique.

“One of the really crucial things that defines our process is the GD&T process that we’ve implemented on the shop floor. This is a standard that’s been established and adopted by the best precision industries in the world. It establishes a framework that governs best practices for machining. For instance, we climate control our facility to 20 degrees Celsius, and have four HVAC units that control a shop that’s around 14,000 sq ft. The temperature control ensures that the material is consistently process at the same temperature, so you don’t get any abnormal expansion or contraction with temperature swings from the summer to the winter. It also affects all of the fixturing that we utilize at every step of our machining process, and we always reference from a datum A surface, which is the reference surface that is put into the rod at the very first step. For every subsequent machining process, the machining goes back to that reference surface, which allows us to control the tolerances and maintain the accuracy of the dimensions of the rods,” says Moch.

Each rod is tracked in Oliver’s computers — they know when it was made, where the raw materials came from, even who the CNC operator was who pushed the button on the machinery. This is to ensure that they are capable of tracing any problems that may arise in the future, and is a unique level of quality control.

The GD&T process is critically important when it comes to providing concentricity, circularity, parallelism, perpendicularity, and other factors that enable the company to provide superior connecting rods.

“One of the distinguishing characteristics of our connecting rod is our double heat-treat process. We fully stress-relieve the rod after rough machining. We get a blank of material, say it’s around eight pounds, and we CNC-machine down to a net shape, and remove probably about 50 percent of the material from the blank. Then that net shape piece is sent out to the heat-treater for a second heat-treat process, which is a quench and tempering process. This fully relieves all of the machining stresses which are put into the part after the rough machining. These are pretty significant when you remove over half of the material from the initial starting blank. It’s costly and adds a week of turnaround time to a batch of rods, but it’s a significant benefit in terms of getting the complete 100-percent martensitic grain structure into the material and optimizing it,” says Moch.

The machinery is one of the keys to the company’s success; Oliver invested in the most up-to-date manufacturing methods to ensure that the product you receive performs up to expectations, each and every single time.

Roughing the blank down to the net shape before the quench and temper process gives the Oliver team much more control over the grain structure to ensure that each and every connecting rod is identical not only in appearance but in power-handling capability. The heat-treat process has been tailored to the specific needs of the Parabolic Beam rod, which has been developed and perfected over 30-plus years of production. Additionally, the connecting rods are shot-peened to put compressive residual stress into the exterior of the rod’s surface, which helps to prevent cracking and crack propagation. This process hardens the surface of the rod and makes it more durable.

“The big end stays round after people beat these up. I’ve used north of 1,200 sets of these, and I have never, in 1,200 sets, had one rod go bad,” says engine builder Rich Groh of RGR Engines. “I’ve had these come back where the racer rattled the engine so hard that the alignment cap dowels on the rod sheared into two pieces. I’ve pulled those sleeves up, put new sleeves in, resized the rod, and stuck it back in that same engine that was beat up, and run it for eight years — and continues to still run those rods. It’s Justin Burcham’s 6-second Coyote Mustang. That engine has six of the eight original rods in it, and the only reason the other two aren’t in there are because when he hydraulically locked the engine with water, it buckled the rods until they bent. But they didn’t crack or break or spit all over the engine? No.”

Not only is the manufacturing machinery top-shelf, but in order to ensure that those tolerances are held to the highest standard, the measuring equipment must be as well. This Zeiss VAST XXT Coordinate Measuring Machine is highly accurate, allowing Oliver’s QC team to ensure the connecting rods have the optimum tolerances.

Each set of Parabolic Beam connecting rods is matched to within less than two grams of variation (equivalent to the weight of two $1 bills) and are honed to plus or minus .0001-inch. The mating surfaces of the cap and rod are precision ground, and the final inspection the company provides as part of the GD&T process ensures the rods are built to last.

Premium ARP 7/16-inch cap screws are used in the connecting rods that we used in our Pure Evil project. The unit shown here are the Standard Light Parabolic Beam pieces (PN F5933MDLT8) that use .866-inch wrist pins. These heavy-duty connecting rods will help us to sustain near-five-digit RPM levels and remain reliable, year in and year out thanks to the exacting manufacturing methods used in the Oliver Racing Parts factory.

“They are made in America, with true American quality. I can’t say a single bad thing about them. There truly is something magic about those rods, and their strength and ability,” sums up Groh.


Oliver Racing Parts

(231) 237-4515

RGR Engines

(630) 488-7966

Mike Galimi
Mike Galimi
Mike Galimi is the Director of Content & Marketing at ProMedia Publishing and Events with nearly 20 years of experience in motorsport writing and photography.