Here is a rendering of an...
Here is a rendering of an F1-Inspired Steel Rocker from Del West.
Del West Engineering has been showcasing rockers with a Diamond-Like Coating (DLC), cam-shaped tip. Under the correct conditions, a DLC coating (when run on an oil film) can have similar friction characteristics when compared to a conventional roller-tip. From a dynamics perspective, the roller can add significant weight to the valve side of the rocker arm. Non-roller tips can materially reduce rocker MOI. Removing mass from the valve side of the rocker has an effect similar to reducing overall valve mass.
The three highest stressed components in a racing engine are the valve springs, the connecting rods and the pistons. Improvements in spring materials or technology usually result in improved engine performance. In order to optimize valve spring function and durability, spring wire requires the cleanest possible steels to prevent internal defects called inclusions. Advanced heat-treating processes are also required to achieve optimal performance. At the end of the day, the valve spring should be one of the most carefully selected components in the engine build. Simply put, do not cut corners on valve springs.
As engine speeds increase, higher "natural frequency" springs are needed in order to maintain valvetrain stability. Higher natural frequency generally comes from high spring rates. The spring must have enough open pressure to keep the valvetrain under control and sufficient spring pressure to prevent valve bounce at high speed. However, there is a balance between spring pressure and frictional losses, simply because running too much pressure will increase the forces a valvetrain must handle and increase net friction. Running a spring with less than optimal open spring force may reduce the maximum speed the engine will turn safely but could lead to parts failures.
Selecting the correct spring is one of the most critical aspects of valvetrain development. Without a Spintron (or comparable spin fixture) to develop your valvetrain, it is best to seek advice from the cam designer and spring supplier. Once again, don't overlook the fact they designed the part.
Changing one part in the "system" may affect the performance of the valvetrain as a whole. Here's an example: Improving pushrod stiffness will reduce pushrod deflection, thereby increasing the duration of the valve events in the same way achieved by installing a cam with longer duration as shown in Graph C on page 40. If the cam was optimized for the original valvetrain and stiffer pushrods were installed in the engine, it would behave as if the cam was too large.
Do not assume that the lift or duration of your valvetrain (as measured statically) stays constant with engine speed which is in a dynamic environment. In fact, valve motion for pushrod valvetrains changes with engine speed. Graphs D & E show how both lift and duration change with engine speed, for a NSC-type valvetrain. The changes you'll note in duration and lift are due to the deflection in the valvetrain. And, although Saturday night engine packages don't compare directly with these data, you can expect similar tendencies to exist and should consider how "flexible" valvetrains can impact your particular engine.
At the outset of this series, we promised to provoke some thoughts, along with providing you a few ways to think about (or re-think) your approach to building weekly racing engines. Obviously, not all aspects of Cup engines apply to making power with mainstream circle track applications. But if we have been able to shed some useful tidbits that'll save some money and time while putting you nearer the checkered flag, mission accomplished.
It would be foolish to assume we've addressed all your concerns or interests. In an "extended classroom" like CT's forum, you can't raise your hand with a question or comment. But in this case, let e-mail to CT become your channel of communication, and we'll do our best to either respond directly or build a piece of editorial that expands on the information you're trying to nail down. And don't forget the quote from Smokey we previously shared, "To finish first, you damn well first have to finish." Meanwhile, don't spin out.