Then at 6k rpm it will produce 2Y airflow. As its name implies for each RPM the amount of airflow it pumps is ‘fixed.’ IOW, its airflow is linear. Now a positive displacement (also called a fixed displacement) blower produces airflow in a totally different way. 64psi! Talk about severely overboosting!! Again the driven speed doubled so you square the boost…. If you tried to set the pulleys up so you hit 8psi at 3250 rpm then figure out how much boost you would have at redline. Then you can figure that at 3250 rpm (half SC driven speed) you now how the square root of the boost at 6500 rpm… or 2.8 psi. So say you had it set for 8psi at 6500 rpm. This means that at every point below redline you will NOT be at maximum boost. Because of this you need to set the blower so that its max boost occurs at redline. IOW, as RPMs increase the boost level will rise. What this means is the airflow of the blower will increase faster then what the engines airflow requires. At 6k it now delivers roughly X^2 airflow. So say at 3k rpm it delivers ‘X’ airflow. The amount of airflow a centrifugal delivers (literally blows) increases roughly at a square of its driven speed. Now here is the critical difference between a centrifugal blower and a positive displacement blower. If you double the engine speed the superchargers driven speed doubles. As such its driven speed is directly connected to engine speed.
In other words if you double the RPM the engine can consume twice as much air.Īny supercharger is belt driven off of your accessory belts.
If you double the RPM (6k) the engine now needs 2W airflow. Say at 3k RPM WOT it is ‘W.’ An engines airflow needs are linear. Your engine requires a certain amount of airflow at a certain RPM. “What is the principle differences behind a positive displacement and a centrifugal blower? “
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