IGF-1 (Insulin-Like Growth Factor 1). IGF-1 or insulin-like growth factor 1 (brand name: Increlex) is a growth factor which is very closely related to insulin. It carries the same amount of amino acids as insulin and responsible for the anabolic reactions to GH.
Spring pressure is the key factor in determining which spring should be used for which application. Camshaft design also plays an important role in determining which spring you will need. Lift is the critical spec when matching valve springs to the camshaft. The more lift you have the greater the pressure needs to be.
Also valve cracking pressure is the differential pressure required to begin to crack open the valve. So if you have a 5 psi spring, the valve would start to crack open at 5 psi of differential pressure, but it would take more pressure and flow to fully open the valve.