| I am posting here instead of in that thread since the thread is several pages back now, and this information might be of general interest. It is possible to run high boost on a actuator with soft springs by pre-loading the actuator. But IMHO it is not ideal for many reasons. First is that over time using a lot of preload could weaken the diaphram and spring. In all OEM applications you see that the actuators are not preloaded much, and the springs are selected by the manufacturer to meet the boost pressure requirements. Second is that boost response would not be ideal at high boost. Let us consider how an actuator works. Within the actuator is a diaphram and spring that is connected to the actuator rod. When pressure is applied to the diaphram, that gives a force (pressure * area of diaphram) that pushes against the spring to move the actuator rod. The stiffer the spring the less the actuator rod moves, as given by the standard spring force equation: F = kx, where k is the spring constant and x is the distance moved by the rod. When you preload the actuator, the force exerted by the diaphram must exceed the preload force before the actuator rod starts moving. But once it starts to moves, the spring rate is still unchanged. So a preloaded soft spring will still act like a soft spring once the force exceeds the preload. The difference then is at high boost the actuator with soft springs will be more sensitive to boost pressure fluctuations compared to the actuator with stiff springs, because with the softer spring rate the acuator arm will move more for a given change in pressure. This will translate to less stable boost when running high boost. It would also slow down response when building boost. Conversely the side effect of running excessively stiff springs at low boost is that you are more likely to experience boost creep, because the actuator with stiff springs may not be able to open the wastegate flapper enough to bypass enough exhaust to hold that low boost. So in general it is desirable to run a actuator spring that is matched to the boost pressure you want to run. Typically the range that you can control properly with an EBC is from +0 to +10psi over the base boost pressure (the boost pressure the car develops with EBC turned off).
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