"We equate the importance of valvetrain stiffness with valvetrain component weight reduction. Our testing has revealed component deflection can cause up to 20 degrees of valve duration loss. Even over a range of only 2,000 rpm, duration losses from deflection of parts can amount to 5-10 degrees. Because of this deflection, cams need to become 'too big' at low rpm and then (because of component deflection) are 'too small' at higher engine speeds. By increasing push-rod o.d., cam journal size and rocker arm stiffness, engines will perform better at both low and high rpm since cams will then run closer to their design specifications.
"Cup engine development has really provided something here for the Sportsman racer. Despite what we've previously believed about heavy valve springs, it's now apparent (when the issue of valvetrain stiffness is properly addressed) the smallest spring that will control the system is the best choice. Excessive spring loads result in heavier springs (or the opposite is true), and the latter aggravates valvetrain deflection and friction horsepower losses.
"With respect to valvetrain component material selection, the Sportsman racer now has an opportunity (based on Cup engine investigations) to select from tool steel spring retainers that simply perform comparably to aluminum or titanium parts, at a penalty of only about 1-2 grams of weight. These are well suited to Sportsman-type engines because they're more affordable and increase valvetrain performance over time, owing primarily to the fact they help maintain the distance to coil bind longer.
"And speaking of coil bind, we've found this to be almost (if not more) important than spring load. This is because much of a spring's internal dampening occurs at maximum valve lift, near coil bind. If excessive clearance is provided (short of coil bind), the spring is not able to provide adequate harmonics damping. In Sportsman engine applications, a clearance range from 0.050-0.100-inch from coil bind seems to work best. The more controlled a valvetrain becomes, the closer to spring coil bind it likes to be run.
"Sportsman racers cannot individually afford the amount of dynamic testing required for Cup engines. However, they can benefit from some of the results these tests produce. Whenever possible, it's best to work with a camshaft (valvetrain component) manufacturer who is involved in these type test programs. At COMP, we've spent an inordinate amount of time and resources in an ongoing effort to be involved with such activities. And, wherever possible, we've allowed the knowledge thus gained to trickle down into our products that relate directly to the Sportsman racer community.
"I also think that it's important to note how easily a given valve spring assembly (springs, retainers and locks) can be taken apart. If it takes a sharp rap with a hammer to separate retainers from locks, suspect there're valve control issues afoot. But if it only requires a light tap, chances are good no problems exist. Sportsman racers should pay particular attention to wear at the interface between spring and retainer. For these engine packages, this is one of the first areas to exhibit abnormal wear."
As mentioned in a previous part of this series, knowledge continues to be power-including horsepower. The breadth of an understanding about virtually any topic creates advantages. In the case of this series of stories, you have an opportunity to benefit from the investments Cup teams have and continue to make in their respective programs. Learn, enjoy and use to your racing advantage.