So where do recommendations for springs that have over 200lb on the seat come from? To understand that, you must first appreciate that a valvespring has two jobs: first it has to provide enough force to hold the valvetrain together. Second, it has to control its own mass.
In high speed operation, valve springs vibrate. This vibration is termed “surge”. Have a look at this YouTube video of a surging valvespring. When a valvespring surges, the load on the retainer oscillates and reduces the load available to keep the valvetrain together. Now the picture becomes more clear: when a spring is out of control with surge, the installed load must be increased to compensate. The opposite is also true: if surge can be reduced, the installed load can be reduced also.
How is surge reduced? There are a few ways to do this. First, the profile can be made softer so it excites the spring less at the speeds you want to run. This improves durability and control at the expense of performance. Second, friction damping can be added to the spring. Lots of offshore performance engines use this technique in the dual spring with flat wire damper, and it’s been around forever. Damping can also be achieved through running an interference fit between the inner and outer spring without a flat wire damper. Other solutions have been used with success like metal and plastic dampers that contact the OD of the spring. The problem with all these friction damping solutions is that they make heat, and lots of it. They stress the oil and cause it to oxidize.
What if there was a way to damp surge without adding friction? There is, and it’s called rate modulation. Springs can be designed such that their rate changes as they are compressed. When the rate changes, it disrupts the surge and increases damping, all without adding friction and heat.
