Engine building often requires innovative problem-solving, and one approach that frequently sparks debate is running solid roller lifters on a hydraulic roller cam. While unconventional, this method can effectively address specific performance issues when executed correctly.
Daniel Powell from Powell Machine recently delved into this topic, addressing questions about Steve Morris of Steve Morris Engines. Morris, while working on a blower-equipped LS engine with a hydraulic roller cam, used solid lifters to solve valvetrain issues. Here’s a detailed breakdown of why and how this was done.
Why Use Solid Lifters?
Hydraulic lifters are well-known for their convenience and self-adjusting nature, but in high-performance applications, they can falter under extreme conditions. Problems like lifter pump-up or bleed-down often arise at high RPM or under boosted conditions, compromising valve timing and engine performance.
Switching to solid lifters eliminates the unpredictability of hydraulic lifters in such situations. As powell explains, “This was the solution. I mean, if you’re going to run a hydraulic profile in an application like what they’re trying to do here, to me straight out of the gate, it would have been a solid lifter and call it a day.”
Lash Settings
When running solid lifters on a hydraulic cam, proper lash settings are critical. Powell provides a clear explanation of the math involved: “In pretty much all hydraulic profiles, the lash ramp is at .004 tappet lift. So, for instance, on LS it’s a 1.7 rocker. So therefore, you would set the lash if you had a solid lifter on a hydraulic profile — you would set the lash at .007 inch. That’s what the math says.”
While .007 inch is the standard starting point, Daniel added, “Having said that, keep in mind that hydraulic profile almost always is going to have, at that setting, it’s going to have a lower velocity and acceleration than an actual solid profile. So, having said that, you could loosen the lash a thousandth or maybe two-thousandths of an inch more without any real problem, as long as you’ve got a rigid valve train.”
Daniel also emphasized the importance of verifying lash across temperature ranges: “Make sure when you set the lash hot that you let the motor cool off and check the Lash and make sure that you’re not hanging a valve open.”
Hydraulic Vs. Solid Profiles
While running solid lifters on a hydraulic cam works, it comes with inherent limitations. Hydraulic profiles are designed for smoother operation, with less aggressive ramp velocity and acceleration compared to solid profiles. As Powell explains, “With a solid profile, you can just put so much more velocity and acceleration in the lobe. You don’t have to worry about freaking out the hydraulic lifter.”
In this case, the solid lifters fixed the lifter control issues and allowed the engine to reach higher RPM without nosing over. However, Daniel suggested a different starting point: “If you’re going to have a solid lifter and springs for a solid lifter, then why not have a solid lifter profile? You might as well take advantage of area under the curve and call it a day.”
Issues with Hydraulic Lifters
The LS engine in question had a combination of factors that overwhelmed the hydraulic lifters: high RPM, significant spring pressures, 3/8-inch pushrods, and steel intake valves. “All of that added together equals train wreck for hydraulic lifters,” says Powell. “Hydraulic lifters are super sensitive.”
One of the primary issues with hydraulic lifters is their tendency to pump up during valve train lofting. Daniel elaborated, “When you get some lofting over to nose, then the lifter pumps up, and then it takes a minute for it to catch back up, and then it just kind of loses control. Or the lifter bleeds to death, and then the cam just gets smaller and smaller and smaller as RPM increases because the lifter is bleeding out.”
In boosted applications, the problem is compounded by pressure behind the intake valve: “Keep in mind, when you got forced induction, all of that pressure is behind the valve. The valve is trying to close, there’s pressure behind it, and it’s trying to blow it back open.”
Daniel offered valuable advice for those considering similar setups. For boosted applications, he recommends lighter valvetrain components: “You’ve got to run little push rods, you’ve got to run the lightest valve money can buy, so that you need the least amount of spring pressure to do the job. They’re just sensitive.”
Ultimately, Daniel concluded that while using solid lifters on a hydraulic cam can work, it’s often better to opt for a solid cam profile altogether, saying, “Just go solid and call it a day.”
Running solid roller lifters on a hydraulic roller cam is a practical solution for diagnosing and resolving hydraulic lifter issues in high-performance setups. However, it requires meticulous attention to lash settings and an understanding of the trade-offs involved.
As this case demonstrates, solid lifters can stabilize the valvetrain and restore engine performance. Still, for long-term reliability and maximum output, starting with a dedicated solid lifter cam may be the better choice.
For those tackling similar challenges, remember Daniel’s advice: “If you’re doing all this, just go solid and call it a day.” Success lies in the details — and that’s where the magic of engine building truly happens.