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Crane Hydraulic Roller Lifters

8,500 RPM!

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There are very few sounds sweeter to a gearhead than a small-block spinning past 8,000 rpm. For anyone who appreciates internal-combustion engines and horsepower, a race engine spinning at high rpm is hypnotic. But for most street-car enthusiasts, engine speeds above 6,500 rpm (and certainly beyond 7,500) might as well be a bench-racing fantasy. The point of high rpm is power. If the engine can make good torque at a higher engine speed, it will make more horsepower. But in order to reliably achieve those stratospheric engine speeds, conventional wisdom holds that you have to run mechanical roller lifters, monster valvespring pressures, and expensive shaft-mount rocker systems—and those are just the valvetrain pieces. So when the guys at Crane claimed they had a hydraulic roller lifter that would live at 8,000-plus rpm, we were interested. The team of Westech Performance's Steve Brulé and Crane Cams' Chase Knight collaborated to assemble a small-block Chevy that we would spin to 8,500 rpm, just to show that it could be done. And it did—many, many times.

This was not a one-trick-pony deal. We didn't just hammer it once and call it good. Steve ran this small-block up on Westech's Superflow 904 dyno multiple times, working his way up from 7,500 to 8,000 and finally to 8,500 rpm. So that's the large-print headline—but the real story is how we got there—and why. That brings us to all the juicy details you'll need to know should you want to duplicate this effort.

Why Go There?

This is the go-to question. Don't we already have entire catalogs of mechanical roller camshafts and stiff springs that will achieve mega rpm? The obvious answer is an unqualified yes. So let's start this discussion with a qualifier that even with a killer 8,500-rpm valvetrain, you still must have an extremely reliable rotating assembly to be able to withstand these engine speeds. This means a high-quality forged crank, forged pistons, and stout connecting rods. Stroke obviously plays a part in this equation, as well, since the G-loads imparted on a piston and rod assembly at a given rpm are directly affected by stroke. A 3.00-inch-stroke 302 small-block Chevy piston travels a much shorter distance than a 4.00-inch stroke small-block at the same engine speed. Therefore, the long-stroke piston must travel much faster and accelerate away from both TDC and BDC much quicker at this same speed. RPM is the great determiner in terms of engine durability. We've grown accustomed to seeing NASCAR small-blocks spin to 9,000-plus rpm on television, but that doesn't mean that your stock small-block will live at those speeds.

Assuming we have an engine that will live and make power at 8,000 rpm, why would you want to go with hydraulic roller lifters as opposed to a mechanical roller? Let's start with the fact that mechanical roller cams all require lash or clearance while running. Long idle periods combined with wide lash specs can cause problems. According to the Bosch Engineering Handbook, needle roller bearings are very impact-load sensitive. This means that constant hammering of the lifter against the cam lobe can cause a flat spot on the tiny roller bearings. Once that happens, it's only a matter of time before the bearing fails. Since mechanical roller cams require a lash setting of somewhere around 0.014 to 0.020 inch, this is an issue. Hydraulic roller lifters, on the other hand, operate with a preload that creates constant contact between the roller lifter and the cam lobe, which (in theory) is an inherent advantage in favor of the hydraulic lifter concept.

Keys to RPM

We spoke at length to Chase Knight at Crane Cams about these 8,500-rpm small-block lifters to understand why this system works so well. Knight emphasized that professionally matched components that are proven to work well together is key. Crane has put major research effort into matching valvetrain components that they know will withstand these high-rpm ventures without failure—effectively, a system's approach to the valvetrain. If you are serious about valvetrain development, you either own or have access to a Spintron. This is a machine developed by Bob Fox, which allows valvetrain developers to test components like cam lobe profiles, lifters, valvesprings, retainers, valve locks, pushrods, and rocker arms for durability and compatibility. The key to a successful high-rpm hydraulic roller valvetrain, according to Knight, is a combination of lightweight and high-strength components. An example would be pushrods. This 8,500-rpm hydraulic roller lifter 355ci small-block is stout not just because it was able to achieve a very stable rpm curve. The amazing part is that it did it using street version 5⁄16-, 0.080-inch-wall pushrods and a stud-mounted rocker system. Most professional engine builders would recommend at least a shaft rocker system, along with custom, 3⁄8-inch-diameter pushrods to achieve even greater stiffness.

Of course, not just any hydraulic roller lifter is capable of such performance. Knight says Crane's lifter starts with an 8620 steel body that is heat-treated and carburized to increase the lifter body's surface hardness. Crane also makes all of the lifter's internal components and select-fits these pieces to ensure internal clearances that are measured in microns instead of thousandths of an inch. A micron is 10^-6 meter or 0.000000393 inch. This means that typical bearing clearances where you might measure to 0.0001 aren't nearly precise enough. Knight says measurements for these lifters are magnitudes tighter. Knight also warned, "Hydraulic lifters are the engine's most efficient oil filter," which means that keeping the oil clean will also be of great benefit to maintain the lifter's efficiency. If debris is allowed to contaminate the lifter, the check ball will stick open and allow the lifter to bleed down, which is not good.

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