Performance Upgrades How High-Lift Camshafts Interact with Hydraulic Lifters

The prospect of having a high-performance camshaft is simply appealing: higher power output, engine performance that is breathtaking, and perhaps the main reason, a large increase in engine output. In many cases, emphasis is put squarely on the idea of lift and duration increase the values that determine the extent to which the valves open and the length of time they should open. Nonetheless, the combination of these aggressive profiles, and in particular high-lift designs, together with standard hydraulic lifters needs to be approached with caution. This is essential in knowing how to make the upgrade successful and reliable.

Understanding Camshaft Lift and Duration in High-Performance Engines

Simply put, a camshaft is responsible to open and close the valves of the engine. Lift is the furthest that the valve will travel when the cam roller is pushing it open and also has a direct connection to both the amount of air/fuel mixture that can move in and out of the cylinder and exhaust can leave the cylinder. Duration is the time (crankshaft degrees) the valve remains off its seat. Compared to stock profiles, lift and duration are increased by aggressive-designing performance cams.

The higher the lift the more air can pass through this is particularly applied at high RPM where the engine is breathing heavily. Greater time, especially overlap (both the intake and exhaust valves' slightly open at the same time) increases cylinder scavenging, which expels exhaust and draws in new charge. This combination opens horsepower and torque, and alters the very requirements of the valvetrain.

Compatibility Challenges: Pairing Performance Cams with Hydraulic Lifters

The self-adjusting aspect of hydraulic lifters makes them popular as they do not require frequent adjustments to valve lash, are quiet, and do not require repeated valve lash adjustments. They hold a small piston and spring in engine oil and have oil pressure automatically act to fill any gap between the lifter and valve train parts.

This very mechanism becomes the challenge with high-lift, high-duration cams:

1. Lifter "Pump-Up": When operated very fast, the opening / closing cycle may lead to pumping up of the lifter internal piston. It is forced out slightly beyond its normal operating position by the oil pressure, which in effect holds the valve wider open longer and higher than it should and at less pressure. This results in:

• Valves are not sealing at high RPM (loss of power).
• A possible valve face to piston contact (catastrophic engine damage).

2. Collapse Under High Spring Pressure: High-performance cams demand much stiffer valve springs to give high closing and avoid valve float (caused when the spring cannot ensure that the valve train stays in contact with the cam). This spring force may overpower the internal spring of the lifter rendering it to collapse a little bit. This takes away performance by reducing effective lift of the cam and cam duration.

3. Bleed-Down Rate Limitations: How fast the oil can change the rate depends on how fast it leaks out of the inner chamber of the lifter. Standard lifters may bleed the valves down too slowly to meet the fast action of performance cams, and add to pump-up. Conversely, lifters designed for higher RPM often have faster bleed-down rates but can be noisier.

4. RPM Ceiling: All hydraulic lifters have a lower natural limit (to reliable running) at maximum operating RPM than solid lifters do, until engine modifications are made to overcome the physics of the oil column inside them. Sometimes high-lift profile can cause the engines to run in RPM areas that normal hydraulic lifters cannot perform.

Supporting Modifications: Springs, Retainers, and Oil System Adjustments

The trick to a smoothly operating high-lift cam used in conjunction with hydraulic lifters is to provide careful ancillary adjustments:

1. Upgraded Valve Springs: There is no compromise on this. High seat pressure and open pressure are needed in performance springs with a considerably higher value. They will have to operate violently on the valve train at high RPM with no float and not collapse the lifters too much. Spring harmonics even become critical.

2. High-Strength Retainers: The springs may be frustrated by the huge amounts of forces exerted by the stiff springs and high RPMs as held by the stock retainers. Safe, solid, high-strength retainers (typically titanium or high grade steel) are a prerequisite to safety and reliability.

3. Oil System Considerations: Engine oil is the lifeblood of hydraulic lifters.

• Stable Oil Pressure: Oil pressure must be sufficient and for the entire working range consistent. The oil pumps may have to be upgraded or modifications to pressure relief valves may be required.
• Oil Viscosity: The right oil viscosity has to be selected. Heavy oils may increase pump-up whereas lighter oils may be too thin to cushion and cause wear or noise. Check the recommendation on cam and lifters. Good quality synthetic oils tend to be popular.
• Lifter Selection: Do not worry about brand names, but know there is a wide range of difference in the quality of hydraulic lifters. Stock lifters absolutely cannot be used and they should be replaced with specific high-performance lift-type lifters whose internal bleed rate ratios have been altered and whose parts are hardened. These have been designed to withstand pump-up and collapse under the tension of an aggressive cam better.

The Takeaway

High-lift camshafts promise great performance rewards, of which engineers are keenly aware, but performance complications are posed by the interaction of high-lift camshafts with hydraulic lifters. Pump-up and collapse are possible threats, which may result in power loss or drastic damage of the engines. Performance Reliability can only be established by doing more than changing the cam. It is vital to invest in perfectly matched, high pressure valve springs, heavy duty retainers, prudent management of the oil system (pressure and viscosity) and lifters selected to be used in high performance duty. Learn the physics here and providing solutions to these essential assistance adjustments and you should be able to enjoy the benefits of a high-lift cam and stay with the convenience of hydraulic lifters.