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Here’s a comparison of pushrods. The pushrod on the left is the standard 3⁄8-inch-diameter steel unit. It works well, but the larger 5⁄16-inch pushrod helps limit deflection and improves valve control. A smaller pushrod may be lighter, but it flexes. The result is that the valve opens later and the lifter can lift off of the cam lobe—neither of which is good. If you experiment with tapered wall pushrods, you can sometimes get even bigger units to work.