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Message: [QUOTE="TARM, post: 117516, member: 578"] Technically to accurately project the area of a valve where manifold and or drive pressure can exert force on you do have to calculate the area its being applied to. While you can use the flat surface area of the face that is not accurate as the force is being applied to area on the backside of the valve. But point in fact you do also need the area of the valve face as well as force is being applied there as well. Its not just as simple as boost or drive pressure. For the force from boost and drive pressure you need to take the area of the valve minus what is covered by the seat (so inner and outer seat measurement will get you that) then you need to also subtract the area of the stem. That will get you the surface inches squared that you can now multiple boost PSI to get the pressure countering the spring, This force will only matter when the valve in question is fully seated. There are of course countering forces from pressure inside the cylinder and if you want to correctly account for those then you would be using the valve face surface area. Its a dynamic event and situation so there many factors going on. But honestly IMO its a lot to do and still will not get you 100% there. The principle job of the valve spring is to ensure the valve follows the cam profile and closes solidly. Where bounce or flutter happen is when this does not happen. RPM and cam profile valve train weight are the primary specs that dictate spring rate. Boost does have an effect but its to a lesser degree IMO. With that said I personally would error on the side of more than vs too little spring pressure.. That does not mean overly excessive spring pressure. Point being is as long as we are under the threshold of damage to parts its best to error on the side of more if this is a perf setup. I think there is much more going on that effects the needed spring pressure than the increases of boost directly. RPM tend to climb at a faster rate and we tend to go higher in rpms band. This is a dynamic event and has to be looked at as such. After doing a good amount of reading on the subject even the engineers can not fully agree on this stuff when it comes to boosted engines. What it comes down to is an educated guess to start out then making adjustments based on experience. The whole idea is to prevent flutter/float and on the other side not to go so high as to have needless wear or strain/failure of other valve-train parts. My only real issue in this thread was the stated 72 lb and 92 lbs for the OEM and 910s when set to OEM spec height they are 110 and 130 respectively. So I wanted to know how that was computed so I could then understand where the 175 lb on these new springs rate in relationship to those and what the install height is etc... I am not saying either way whether in terms of proper spring pressure. My feelings are if you plan to push your engine and its a higher perf build they are likely a good choice. When you go with larger injectors with more air capacity you are increasing your rpm limit and from that alone there is more force. Add to that a new cam profile with faster rate which adds to that need even more. Then finally account for the effects of the higher boost as needed. Break in the springs running them easy and letting cool to take the initial set before romping on them. Then hope there is no float ( popping) when you take them up to redline. If there is add shims to get needed tension or order new ones. The guys that are install new/reground cams you are installing new lifters as part of the install, yes? Welding the cam gear on to prevent walking as well? [/QUOTE]