When a four-stroke, two-valve-per-cylinder, pushrod engine operates at 6,000 rpm, the intake and exhaust valves are opening and closing 50 times per second. And that's at only six grand, where some engines are just waking up.
Building a valvetrain to handle those kinds of stresses and at the same time produce power under competition conditions requires paying attention to a lot of moving parts.
"It isn't just flow; it isn't just lift. There's a lot of things you have to worry about in the valvetrain as an engine builder," said Claude Holguin of CHE Precision, Newbury Park, California. "All this has to work together."
Holguin was one of several valvetrain experts we spoke to about how to keep a valvetrain from failing under race conditions. In what follows, we'll unpack in greater detail those "lots of things" he referred to.
Lobe Design
Camshaft lobe design plays a big role in "being easy on valvetrain parts," said Bobby Biancaniello of Cam Motion, Baton Rouge, Louisiana. "To look at the valvetrain and why valvetrain parts fail, you have to start with the camshaft, especially in hydraulic roller applications. If you're trying to accelerate the valve off the seat extremely quickly, you can piss off a hydraulic lifter pretty easily. And if you have some deflection on opening, you're definitely going to have some seat bounce on the closing. That's hard on valve seats, it's hard on valves, and the valve springs won't last as long."
"If a part deflects—be it a rocker arm, a pushrod, a retainer—kind of bowing a little bit, all of those become springs," said Chris Potter of COMP Cams, Memphis, Tennessee. "They absorb energy, and then they give energy back. The more we understand that and help control that through lobe design, the better the engine is going to perform."
Lifers & Pushrods
"The bottom line is, the bigger the lifter, the stronger the lifter," said Guy Aguayo of Crower Cams & Equipment, San Diego, California. "We sell an 0.842-, 0.874-, 0.903-, and a 0.937-inch lifter. On the Fuel end, the big lifter is 1.062-inch. We sell them in needle bearing and bushing styles."
Crower's oiling recommendation for both kinds of lifters is a HIPPO system, which stands for high-pressure pin oiling. "It feeds oil to either the bushing or the needle bearing as the engine has oil pressure," Aguayo said. "In the golden days—or let's call it a few years ago—you would just rely on splash oiling, the splash coming from the rotating of the engine. That doesn't cut it anymore."
Bigger is better thinking holds true for pushrods as well, Aguayo said. "The more spring pressure, the more pushrod you're going to need to keep them from flexing. You don't want it to flex, because you're losing camshaft lift out of the flex of the pushrod."
Pushrod length is important "to get the proper geometry," said Jay Ryan of S.B. International (SBI), Nashville, Tennessee. "Even though the engine might be based on an OEM design, that doesn't necessarily mean that's the geometry you should go after, because there's going to be a lot of changes in that geometry, with rocker arm ratio, lengths of valves, tip lengths of valves—all those things factor into that pushrod length."
He also said to "use hardened chromoly pushrods, especially when you're dealing with high lift cams and higher rpm. This will assist in avoiding deflection or breakage. Pushrods tend to bend a little. So a chromoly hardened rod, with an 0.080-inch wall thickness, is very common."
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