We asked valve spring suppliers for their thoughts on selecting a valve spring rate for a specific application. “It’s not a simple calculation,” answered Jason Youd of PAC Racing Springs, Southfield, Michigan. “Almost everything in the engine affects the performance of the valve spring. You need to understand the application, and all the forces on the valve spring. At a 20,000-foot view, one should reference Newton’s first and second laws of motion.”
“There’s really no go-to formula,” Michael Tokarchik of Manley Performance Products, Lakewood, New Jersey confirmed, “but in general you want the highest natural frequency and the lowest possible mass. That goes back to what we said before about dual springs replacing triples, and a single spring replacing a dual if the lift allows it and it’s not too highly stressed.”
Mike Schropp of Livernois Motorsports, Dearborn Heights, Michigan, believes you can “narrow down the choices fairly quickly” based on the camshaft and other factors, “but this is where engine builders and spring manufacturers can offer a wealth of knowledge to help guide the customer to the appropriate valve spring.”
Most of our valve spring suppliers, in fact, deferred to the judgment and experience of their engine-building customers. “It’s really up to the engine builder,” said Kerry Novak of Crower Cams & Equipment, San Diego, California. “One drag race engine builder will say ‘I need 450 pounds on the seat and 1300 open’, and the next builder building the same engine will say, ‘That’s insane, that’s absolutely crazy.’ So it really is the engine builder’s choice. We can give them a basic number, but they pretty much tell us what they want.”
Chase Knight of Crane Cams, Daytona Beach, Florida, offered this much guidance: “Particularly among drag racers, and not so much among road-race or small-engine folks, we find the idea that more is better. So many of them are running way more spring pressure than they need. Yes, it controls the valve train; but it also wears things out quite a bit quicker.
“That’s why the greatest thing to come along in decades is the Spintron. Not every shop has one, because they are pretty expensive, and you need a specially modified engine block. But if you afford to spend a day with someone who has one, you can learn a lot about your setup.” And what you are most likely to learn is that “you can run less spring pressure and make everything last longer. That will make a day with a Spintron pay for itself.”
As an example, Knight cited Crane’s own Spintron test of “a typical Super Gas or Super Comp big-block Chevy, with .800 lift, and designed to turn 72-7400 rpm. But instead of .120-wall pushrods we used .080-wall, and stud-mounted rockers with a stud girdle” instead of a shaft system, “and stainless steel rather than titanium valves—something a mortal person could build. And we started out with 320 pounds of spring pressure on the seat and 940 open, and this engine ran effortlessly, with valvetrain stability, at 9000 rpm. And then we pulled about 100 pounds of spring pressure out of it, and it still ran effortlessly at 7500.”
“For a lot of racers,” Schropp concluded, “the most challenging thing is getting the right information. The better you are able to guide your customers to the components that match their application, the easier you make it for them.”
For full coverage of the latest in Valve Springs & Rocker Arms, see our feature article in the May 2014 issue of Performance Racing Industry Magazine.