S63 High Performance Valve Spring Kit | BMW M5/M6/M8/X5M/X6M

Theory

The goal of a valve spring pressure is to make it as low as possible. This is because compressing a spring takes energy and robs potential power. In addition, more valve spring pressure increases valve train wear. We work very hard at running just enough valve spring pressure to keep the follower in contact with the camshaft but no more. If you increase the RPM you increase the valve spring just enough to manage the inertia from the increased RPM. The valve spring also needs enough seat pressure and the correct frequency not to bounce when the valve is closed. This is to avoid leaking trapped mass (the fuel air charge).

Boosted Engine

With a boosted engine you will need a slight increase in pressure to push back against the boost pressure in the intake trying to hold the valve open. This amount of pressure added is much less than the pressure to control the inertia of the valve train.

Conclusion

If you double the boost pressure you do not need to double the spring pressure since only about 20% of the spring pressure is to control the boost pressure and 80% is to control the valve train mass. An additional 20% of valve spring pressure is all you need to run.