 |  | | | In most engines, pushrods are pushrods. But in a high-performance application, hidden power could be lurking in the valvetrain. To find out how much power, we discussed pushrods with a few "name" engine builders. The consensus: A bent pushrod or two can cost between 5 and 15 (or even more) horsepower on a street engine, depending upon the camshaft specifications. On a race engine, the power loss can be even more significant. Just as important, some power can be gained by reducing the overall weight of the pushrod, but without sacrificing pushrod stiffness.
Stiff vs. Heavy
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In the "old days," pushrods that bent and flexed were common. The solution was almost always the same: Install the biggest, beefiest, strongest pushrod you could find. The "new" pushrods didn't bend, break or disintegrate, but they were heavy. In reality, the "small" diameter pushrod wasn't the root of the problem. Instead, it was likely a combination of inferior pushrod construction, poor valvetrain geometry and all sorts of internal engine harmonics.
As an example of the harmonics, a certain amount of vibration is passed along from the crankshaft to the cam and eventually into the pushrod. Large-gear, high-pressure/high-volume oil pumps compounded the problem. Each time the engine oil pressure overcame the spring pressure in the pump bypass, it would open and dump oil back into the pump inlet. The oil flow was momentarily starved.
As the big pump cycled, the loading on the oil pump gears and the pump drive became jerky. Not only did this drive the distributor crazy with spark scatter, it also delivered all sorts of weird harmonics to the camshaft and, eventually, to the valvetrain. Large-volume, high-pressure pumps only aggravated the situation.
In the end, one of the biggest problems with vintage pushrods was their pressed-on ends. Often, these ends physically moved as the valvetrain went through its cycle.
When the problem was solved by increasing the size of the pushrod, the stiffness was also increased. Like swatting flies with a sledgehammer, this was overkill. The overlooked consideration was the pushrod's overall weight, including the oil. Large-diameter (7/16-inch) pushrods were larger on the outside but also on the inside. In many engines, the pushrods are always full of oil when the engine is running, and big pushrods hold about 17% more oil than same-application stock-sized units.
Today's solution is aftermarket one-piece pushrods. Typically, these pushrods are cold-forged from aircraft-quality 4130 chromoly steel tubing for rigidity. Wall thickness is often between .065 and .083-inch, compared to .049-inch wall thickness for standard OE pushrods. Furthermore, the ends on performance pushrods are formed during the forging process, so they can't move. The result is better tip alignment and durability.
Once complete, these new pushrods are usually heat-treated and hardened for strength and wear-resistance (when used with pushrod guideplates) and are centerless ground. Some manufacturers even use a black-oxide finish to improve corrosion resistance. Additionally, finished length among these aftermarket pushrods varies a maximum of only about .005-inch, and longer-than-stock versions are also available.
Installation
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Installation is simple: remove and replace. The rocker arms have to be removed to gain access to the rocker studs and OE guideplates. Once the rocker studs are removed, the guideplates can be easily swapped, then the rocker studs, arms and new pushrods can be installed. Prior to putting in the new pushrods, check them for straightness. Pushrods are straight when they leave the factory, but they occasionally get damaged in transit. Simply roll the new pushrods across a piece of plate glass and watch for wobbles. If they don't wobble, clean the new pushrods and slide them into your engine.
What do you gain from using these pro-quality components? Simple: less weight and more structural integrity. And don't forget about the weight of the oil inside the pushrod. The bottom line is more performance and increased reliability.
Resources
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Competition Cams, www.compcams.com
Crane Cams, www.cranecams.com
Edelbrock, www.edelbrock.com
Holley Performance Products, www.holley.com
Manley Performance Products, www.manleyperformance.com
Milodon, www.milodon.com
Mr. Gasket/Erson Cams, www.mrgasket.com
Proform, www.proformparts.com
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