Why are some heads measured at 10″ of pressure and some at 25″ ?
10″ was a European standard which we used and is suitable for Smaller European engines (as opposed to big US V8’s). We have recently updated our flowbench to one which is capable of 25″ or 28″ pressure. 25″ is the pressure achieved by a normally aspirated engine and will therefore simulate the swirl and tumble effects you can expect which can affect flow. Our power predictions for both pressures are accurate as mathematical predictions (from our Port Flow Analyzer software) and most heads have been verified by an actual engine build and test on our in house Dyno.
