This upgraded oil pressure relief valve kit will boost maximum oil pressure up over the original alloy plunger. This style ball and spring was fitted to all Cooper "S" models until 1971. Please bear in mind that this will only increase the maximum pressure before it is bled off, not increase the idle oil pressure. Installing this typically raising from 55/60 at cruise with a standard type, to about 70 at cruise. This will help keep the valve train cooler and cam fed better, but will create more heat.