Eaton M45 superchrager (Page 2/2) sanderson231 JAN 11, 11:42 AM quote Originally posted by Notorio: Larry, could you please explain how to read that interesting-looking map? And use small words so I will understand Here you go: 1) The X-axis is the volumetric flow entering the supercharger in cubic meters per hour. 2) The Y-axis is the pressure ratio i.e. the absolute pressure of the discharge (psia) divided by the absolute pressure of the suction. 0 psig is 14.7 psia. So with a pressure ratio of 1.5 the discharge pressure is 14.7 * 1.5 = 22.05 psia or 22.05-14.7 = 7.35 psi of boost. 3) The near vertical lines are the RPM that the supercharger is turning. For a belt driven supercharger that will be a ratio to the engine rpm which depends on the size of the pulleys. 4) The contour lines are the thermodynamic efficiency of the compression cycle. If there were no friction, the efficiency would be 100%. If the efficiency is 70% then 30% of the input power is being lost to friction which results in excess heating of the discharge gas. So the higher the efficiency, the lower the discharge temperature. That's a good thing because lower temperature means a denser gas which has more mass per cubic meter Let's assume the inlet air is 14.7 psia (0 psig) and 60 'F. There are 1000 liters per cubic meter. For a 2.8L how much air flow is required? Since it is a 4-stroke engine it only ingests air every other revolution of the crank shaft. Therefore at 5500 rpm: 2.8 * 5500 / 2 * 60 / 1000 = 462 m3/hr. That's if there was no supercharger present and the volumetric efficiency of the engine was 100%. The volumetric efficiency of the engine is a measure of how well the cylinder fills. The way to look at this is what is the maximum absolute pressure in the cylinder during the intake stroke compared to the intake manifold absolute pressure (MAP). At full throttle the MAP will be close to atmospheric pressure. That will be about 100 kPa or 14.5 psia. If the volumetric efficiency of the engine is 70%, the cylinder pressure would only be 14.5 * 0.7 = 10.15 psia. A supercharger reduces the volume of the inlet gas by increasing the pressure. How much depends on the compression ratio and the temperature of the discharge gas. To try to keep things simple let's assume that there is an aftercooler (intercooler) on the supercharger that brings the temperature back down to 60 'F. What inlet volume is required from the supercharger to supply the engine at 5500 rpm with a pressure ratio of 1.5 (7.35 psi boost) if the engine's VE is 70%: 2.8 * 5500 / 2 * 60 /1000 * 1.5 * 0.7 = 485 cubic meters per hour. Without the aftercooler the discharge gas is less dense and there is less inlet flow to the supercharger. Of course, this means less power since the mass flow of air to the engine is less. Hope this helps