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Lifters (Hydraulic)

Hydraulic lifters have been the choice of the automotive industry for many years for several good reasons. when compared to a mechanical lifter, the hydraulics are:

1. Quieter.
2. Low maintenance.
3. An ability to adjust for thermal expansion of the engine.
4. Built in shock absorber, eases stress on valve train.
5. “Bleed Rate” can be designed to accommodate different engine RPM ranges.

Today’s modern engines all use either the standard design hydraulic lifter or the new low friction, high performance hydraulic roller design. Hydraulic lifters are the best for street applications, high performance, and mild racing applications where low maintenance is a primary concern.

What is the difference in the design of a Hydraulic and Mechanical Lifter?
Basically, the hydraulic lifter pushrod seat is moveable, the mechanical lifter seat is not. Both lifter types look the same from the outside, with both having pushrod seats held in by a retaining lock. The pushrod seat in a mechanical lifter usually registers upon an internal step inside the lifter body preventing it from moving (thus it gets the nickname “Solid Lifter”). What’s below the pushrod seat in the hydraulic lifter is a different story. Its pushrod seat is not restricted by a step, but instead sits on top of a moveable hydraulic mechanism which acts like a tiny hydraulic pump. Below this mechanism is valving and a spring to produce an upward force, moving the pushrod seat upward against the retaining lock.

The three lifters shown are (from left to right) solid, hydraulic, and roller. Notice the wheel at the bottom of the roller lifter that helps reduce friction.

Inside the hydraulic lifter (left) there is a plunger and spring. This is an antipump-up design and differs from the solid (mechanical) lifter's internals (right).


One way to change an engine's power profile is to increase valve lift. Valve lift is the amount (measured in thousandths of an inch) that the valve is lifted off its seat, and lobe lift is the amount that the cam lobe raises in radius above the cam's base circle.

Maximum valve lift is determined by multiplying the maximum lobe lift by the rocker ratio. For example, a cam with 0.350-inch lobe lift yields 0.525-inch valve lift with a typical small-block Chevy 1.5:1 rocker arm (0.350 x 1.5 = 0.525-inch valve lift). So if we simply install higher-ratio rocker arms, such as 1.6:1, the valve lift will increase (0.350 x 1.6 = 0.560-inch valve lift).