Originally Posted by Dem768
It's not Magic. Think of it this way..
Lets say, just to keep it simple my valve is one square inch of surface. It has a factory seat pressure of lets say.. 45LBS return pressure. Then I boost my car to 24PSI. That means there is 24lbs per square inch fighting my valve springs. Leaving me with only 24lbs of seat pressure do do the same job it was supposed to do with 45lbs of seat pressure at 7000rpm... Valves can't close quickly enough so they start to float.
I read that before from BogusSVO but I don't agree.
24psi is not fighting your 45psi springs.
Intake stroke - valve is open, pressure inside combustion chamber is same as pressure in intake manifold. Net pressure on valve = 0
Compression stroke - your engine has compression of 150+ psi. So pressure inside combustion chamber is several times higher than 24psi of boost in intake manifold
Power stroke - Pressure inside chamber is even higher than compression stroke
Exhaust stroke - this is about the only time when the pressure in intake manifold may exceed pressure in the combustion chamber. But the intake valve is not moving at that point, so no float can happen.
In my honest opinion, higher valve spring rates are only required for more aggressive cam/higher rev limiter. I run more boost on 7200rpm limiter. You run less boost on 7500rpm limiter. Your valves float, mine don't. I call bullshit on the "I need stiff springs for high boost" theory.