Normally, increasing the installed height cannot be done by switching to valves with longer stems because this can lead to rocker arm alignment problems (and also adds mass to the system). Better options for increasing the installed height are to cut into the spring seat in the head, which requires a qualified cylinder head machinist, or offset valve locks, which raise the retainer height.
Lowering the installed height is good for increasing the seat pressure, and the opposite steps are usually taken. Instead of cutting into the spring seat, you can add shims underneath the spring. Offset valve locks that lower the retainer are also available.
Be careful when reducing installed height if you are trying to raise the spring's open pressure. Increasing the seat pressure too much can lead to durability problems; plus, reducing the installed height too much can cause coil bind issues.
Finally, once you have determined the correct installed height, always use extreme care when installing and removing valvesprings. Never use another metal object to pry or otherwise manipulate a spring. "Any time you use metal on a spring, such as a screwdriver if you are trying to remove an inner spring, you run the risk of scratching the surface," explains Billy Godbold of Comp Cams. "That's a bad idea, because that will introduce inclusions on the surface of the spring, which creates a weakened area. Keep Popsicle sticks or something on hand. As a general rule, never stick anything in a spring that you wouldn't stick up your nose or in your ear."
Coil BindNo matter what size the spring, there is a limit to how much the spring can compress before the coils begin to touch, and the spring can be compressed no further. When it comes to valvesprings, coil bind over an extended period can be disastrous.
"As a general rule, you want at least 0.060 inch of travel in the spring over maximum valve lift," explains Allen Bechtloff of Crane Cams. "On the extreme end of the spectrum, some Cup teams are actually setting up their springs to bind at the very end of the lift. They do this because when a spring binds up, it dampens the harmonic wave traveling through it. But this is not something everybody should do. These Cup teams have done a lot of work on the spintron and know exactly how far they can push things. They are aware of the extra wear this puts on parts and can afford to replace parts regularly to avoid a failure."
The difference between the installed height of the spring and the coil bind height (plus 0.060) is the spring's working travel. This travel needs to be just slightly larger than the total lift for the corresponding valve. When calculating valve lift, don't just look at the cam spec card and the lift numbers. That number is multiplied by the ratio of the rocker arm to get the valve's total lift. For example, if you are running a camshaft with an intake lobe lift of 0.400, along with 1.7:1 ratio rocker arms, the max valve lift is 0.400 x 1.7, or 0.680 inch.
As a general rule, you want no more working spring travel than you need. If you have more than you need, switch to valves with shorter stems-if it won't screw up the rocker arm geometry-to shorten the installed height. This will also help keep your springs in the correct operating pressure range.
Weighty MattersNow that we've got the mechanics out of the way, it's time to move on to other factors that affect a valvespring's performance. One of the greatest concerns with any racing valvetrain is the total mass of the system. It may at first seem counterintuitive, but a lighter system can be more durable and work better than heavier components.