High Performance Connecting Rods - Rod Report

Jake Amatisto Jul 29, 2013 0 Comment(s)
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We often talk about how easy it is to make horsepower these days, giving praise to cylinder heads and camshaft technology, but if it wasn’t for tough bottom end parts, such as the modern aftermarket connecting rod (the most abused parts in a V-8 engine, next to the wristpins), none of it would be possible. It’s because of these extremely strong components that we have the option of building as much horsepower as our imaginations/wallets allow; and that’s with an array of power adders and cubic-inch options. Even “budget” con-rods can handle horsepower that was unheard of just 10 years ago, and that’s thanks to an innovative aftermarket.

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We started looking into connecting rods for an upcoming small-block build and we realized there are quite a few options out there. From overall design, length, and processes, connecting rods these days feature some trick attributes that are in place to handle any revving, high-powered engine. Companies like Eagle Specialties, for example, started offering their products with a process that results in a gleaming finish, which they claim strengthens and helps windage. And Scat, for example, has come up with some exclusive designs too, such as their Ultra-Lite line of rods that are great for high-rpm engines. It’s innovations like these that make building a high-powered, long-lasting engine possible.

In the following pages we delve out some knowledge from the top four manufacturers of aftermarket connecting rods, covering what’s available for all levels of performance, and even show off some of the toughest connecting rods out there for those who want to make thousands of horsepower—yep, thousands.

Bushed or Pressed
Research connecting rods and you will find that there are two basic ways pistons are mounted to them. A bushed rod features a bronze bushing in the small end that the wristpin slides through, and requires Spirolocks or round wire locks to retain. When it comes to high performance, bushed rods are more common, however the companies listed in this article do offer both styles. A rod that requires a pressed pin takes a hydraulic press to install (factory pistons are typically pressed on), however these rods are for low performance and rarely get used in our high-performance world.

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WristPins & Retention
Here are some examples of wristpins for different applications. The pins on the left are a standard, low-carbon steel design that are typical in high-performance applications and this is what you commonly get when you order a set of high-performance pistons; however, they are different depending on application. Tapered pins, for example, are made gradually thicker toward the center of the pin; this is for high-boost and supercharged applications where tremendous cylinder pressures are forced down on the piston. The taper is to keep the weight down without sacrificing strength. You’ll notice pins also come highly polished, this adds to the strength by eliminating stress risers and imperfections in the metal. At the highest levels of racing, special low-friction coatings are used to keep the pin from galling on the piston, even in low-oil situations. The small, dark-colored pins on the left are for a NASCAR “Cup” engine from Del West and feature a DLC coating that reduces friction. In some drag race applications where massive power adders are used, such as multiple nitrous stages, some pistons are designed to use a thick, but small-diameter wristpin due to the ring package position (it’s lower to keep the top piston ring away from intense heat).

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Here are a few examples of how the pistons are secured to the rods. The clip on the left is an old design that rarely gets used anymore, followed by the more common Spirolock and on the far left, the round wire lock that we see more piston companies going with today. Anyone who’s installed Spirolocks by hand knows what a treacherous feat it can be for your thumbs, so you’ll be happy to know there are tools available that make installation less painful. The round wire locks seem to be taking the place of the Spirolock, however that’s not the latest development in hanging pistons from rods. There is also a button-style retainer that is designed to be much easier to install than these three and doesn’t require tools.

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Rod Terms:

1. Big End
2. Small End
3. Pin Bore
4. Crank Bore
5. Cap
6. Rod Bolt
7. Beam

Connecting Rod Diagram 6/20

Chevrolet V-8 Connecting Rod Lengths
Displacement Cubic Inches Liters Rod Length (inches)
302 4.9 5.700
305 5.0 5.700
327 5.4 5.700
350 5.7 5.700
350 (LT5) 5.7 5.700
350 (LS1) 5.7 6.098
383 6.3 6.000
400 6.6 5.565
396 6.5 6.135
402 6.6 6.135
427 7.0 6.135
454 7.4 6.135
502 8.2 6.135
377 6.2 6.135

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The two basic types of rods are I-beam and H-beam. Some say H-beams look heavier, but can end up being lighter than some I-beam designs, but not in every case. Which rod design is better is an ongoing debate, and we’re not taking sides, just showing off what’s typically offered. The designation comes from when you cut the beam: the end shapes a letter. X-beam and A-beam rods also exist, but are not common in the high-performance Chevy world.

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When building large cubic-inch small-blocks, such as 427ci and larger animals, sometimes the big end of the rod contacts the camshaft and must be clearanced meticulously. Companies like Callies, however, offer rods that have been designed with this clearance in mind.

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