Pushrod flex and deflection will cause loss in power. This is often overlooked when replacing valve train components. Remember, the stiffness of the valve train is critical to preventing power loss and stock pushrods were never meant to run at 6000 or 7000 RPM’s.
Why shouldn’t I use my stock pushrods?
Wear, length and strength are three reasons not to use your stock pushrods.
Wear on the ends of the pushrod where it contacts the rocker or lifter is always a concern. Because of the high loads, it’s important that the radius on the end of the pushrod match the radius of the seat in the rocker or lifter and that it be free of scoring. A used pushrod end may not be worn round and may have score marks on it.
Length is important on a stud mount rocker to assure proper rocker geometry. On a non-adjustable pedestal mount rocker, length is critical for proper lifter preload. Whenever you change anything in the valvetrain pushrod length must be checked.
Strength is always a concern as stock pushrods are marginal for stock cam profiles and spring loads. When higher load springs, faster cam profiles and higher rpm are involved the increased pushrod flexing (pushrod bends then springs back) disrupts valve timing, rpm stability and component durability.
What should I look for in a new pushrod?
Absolute minimum wall thickness of .080″ to reduce pushrod deflection or flex, this also includes the ends (radius) of the pushrod. If you’re running pushrod guideplates the pushrod must be hardened and smooth to be compatible. The radius on the pushrod ends must be correctly sized and with a smooth finish free of tool marks to prevent galling of the pushrod seats in the rocker and lifter.
Should I use a 5/16″ or a 3/8″ diameter pushrods?
Usually the cylinder head design limits the diameter you can use. Without having sophisticated testing equipment, the general rule is to use the most rigid pushrod that will fit. Naturally the 3/8″ diameter is more rigid than the 5/16″ diameter, so if it will clear the cylinder head, use the larger diameter.
Will the extra weight of the larger diameter/thicker wall pushrod affect rpm?
Added weight on the “pushrod side” of the valvetrain is not as important as on the “valve side”. The added power, rpm and valvetrain durability from the lack of pushrod flex is more important.
Do higher ratio rockers affect the pushrods?
Higher ratio rockers will increase the load on the pushrod because the rocker is moving the valve side faster. This means more pushrod flex as the valve starts to open. To get the most performance from higher ratio rockers a rigid pushrod is a must.