Choosing the right turbo part3


6) Choke Line: Overspin Choke Any points plotted to the right of the graph mean the wheel in question is too small and will have to spin too quickly to make the expected boost/power. At these extreme wheel speeds, efficiency goes out the door because the wheel chops the air so badly that the pore density of the charge air will likely cause a dramatic loss of power.

7) Speed Lines: Compressor Wheel Speed This measurement, illustrated as lines across the graph, represents the shaft speed of the wheel. Remember, the faster it spins, the hotter the charge air. This is why they invented intercoolers


The missing pieces of the puzzle here are the engine’s redline speed, the A/R of the turbine side and the volumetric efficiency of the engine. How fast an engine runs will impact the shaft speed of the turbo and when optimal efficiency is realized. The turbine side of the turbo will determine the spool-up characteristics and responsiveness of the unit. Turbine performance and engine redline speed are closely related, and together both of these factors will have a dramatic effect on the efficiency of the compressor wheel.

This entry was posted in Turbo Tech and tagged compressor map on May 17, 2013.