Originally Posted by sapsz28
Anyone out there please. I dont want to make a mistake and watch my hard earned money as all of ours is go up in the air,Due to a lack of knowledge.
Spring pressure is only one part of a complex relationship. The difficult part is how a spring reacts to rate of acceleration put upon it and the dynamic weights it has to move, this applies to both opening and closing and the additive feature of RPMs which is a frequency. These forces interact with the springs natural frequency. So in addition to supplying enough force to keep the valves assembly tracking with the lobe, the frequency response of the spring which is independent of its strength, needs to be kept out of the anticipated rev range of the engine. This can and does lead to some odd combinations when you're looking at this from the outside without the knowledge of any given systems harmonic frequency responses.
All sorts of damping features have been tried, we're currently in the beehive and ovate wire shape period, but in the past, and even now, flat wound dampers have been used to change a spring's frequency response, multiple springs with reverse direction windings to not only increase pressure but to frustrate frequency responses within the desired operating range.
This is a constant battle as you need to use a s little spring pressure as possible to get the job done because of component wear, secondary part bending, and reliability issues but at the same time have enough force to overcome events like lofting the valve mechanism off the cam lobe as it goes over the top. There are three big variable control issues, one I mentioned is lofting where the spring can't control the inertia of the valve system as the valve is opened which allows those parts to continue lifting the valve after the peak of the lobe has passed out from under the lifter. When the spring gains control of this situation it slams everything back into the lobe with a lot of impact. Adding to this situation is the bending of parts under load. The push rod and studs do most of this but the rocker also has a contribution as they try to escape the applied forces by bending. All this uncommanded motion is why top racing classes use a solid rather than hydraulic lifter. The problem with hydraulics is that they chase any looseness they see in this motion. They see this lost motion space as lash to take up which results in what's called pump-up. So the lifter essentially gets taller and finally reaches a point where it won't let the valve back on its seat till the lifter bleeds down which requires a reduction in RPM which it achieves for itself by blowing off the compression by holding the valves open for a few moments, thus slowing the engine RPMs.
Stiff push rods, large studs and stud girdles as well as stainless steel rockers are all attempts to eliminate these extraneous motions from the valve train. Needless to say the stiffer the valve springs and the heavier the valve train components the worse these bending moments become. So this becomes a circular argument as to how to maintain valve control with ever heavier parts and more spring pressure, obviously more engineering needs to go into the problem than simply bigger is better.