How to read a turbo compressor map - the short course
A compressor map is created under ideal conditions, on a hot gas test stand. These operating conditions would be very
difficult to duplicate in your engine. We utilize these compressor maps as a tool to get us closer to an ideal (compromise) for a given application.
A compressor map is made up by a grid
of pressure ratio versus mass flow in lbs/min (pounds of air per minute) showing the different efficiency-islands (shown in %) and speed-lines (RPM) of the compressor.
Pressure Ratio is; Atmospheric Pressure + Boost Pressure divided by Atmospheric Pressure.
Example given is for sea level:
14.7 psi(Atmospheric Pressure) + 14.7 psi(Boost)
D I V I D E D�� B Y�������������������������������������������������� = 2:1Pressure Ratio
14.7 psi(Atmospheric Pressure)
Mass Flow, LBS / Minute
As a rule of thumb, we calculate 10HP / lb air of�mass flow @100% Volumetric Efficiency, on gasoline powered applications. (This can vary depending on factors such as the overall efficiency of system, engine management tuning, etc.)
You need to estimate how much horsepower (mass flow) your engine is going to make (horsepower goal), then divide this number by 10 (gasoline @ 100% VE), this will give you the mass flow in lbs/min, this number is applicable to the horizontal numbers on the compressor map.
You also need to know the boost pressure you are going to be running at your horsepower goal in order to calculate the pressure ratio (see formula above), this number is applicable to the vertical numbers on the compressor map. It is now possible to find the spot on the map that the compressor will operate at the instant your engine is at the given (power & boost) operating parameters. The idea is to stay to the right side of the surge line and stay within the highest (average) efficiency islands in the operating range of the engine. Another consideration is not to excede the choke flow of the compressor, as this will put undue strain(overspeed) on the wheel and it will create more heat due to the lower efficiency.
An engine is dynamic in operation and in reality it takes hundreds of calculations like this to fully utilize the compressor map, and you still need to test it all in the vehicle to verify the turbocharger / engine match.
We have thousands of applications behind us and chances are we have already been�involved in turbocharging an�application very similar to yours, we can shortcut this process based on many years of experience and our extensive knowledge of turbochargers. Call us for your next turbocharger, we will take care of your power needs.