What is Speed density?
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From: Fairbanks
What is Speed density?
I know what a Mass Airflow sensor is (not really what it does), but what is the difference in a Mass Airflow system compared to Speed Density? What is Speed Density?
Last edited by jimbo285; Jun 12, 2011 at 03:03 AM. Reason: Spelling
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From: Harrisburg, NE
while a mass air flow directly measures how much air an engine is using, a speed density system uses the vacuum reading from the MAP sensor and the throttle blade angle and calculates how much air the engine is pulling in.
biggest problem is with a new cam that has improved the airflow, the speed density can't see it and thinks that it is still drawing in what a stock engine is. preventing it from achieving the proper air/fuel ratio.
biggest problem is with a new cam that has improved the airflow, the speed density can't see it and thinks that it is still drawing in what a stock engine is. preventing it from achieving the proper air/fuel ratio.
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From: Gateway to the West
muscletruck's explanation cannot be bettered without getting into tedious details.
However, jimbo, since you asked/alluded to this...
The mass air sensor works in conjunction with the TP and MAP sensors in MAF applications. All three sensors are employed to pinpoint volumetric changes.
MAF sensor uses a pair of heated wires (think of the heating element in your toaster) to determine the volume of air entering the engine. One wire is in the air stream while the other is shielded and only exposed to ambient air. The computer sends voltage to both wires and heats them up. The shielded wire is sent voltage and as it heats up the resistance changes and so does the voltage returning to the computer. The computer is "looking for" a specific voltage from this circuit. Once this target voltage is received, baseline has been established for the particular atmospheric conditions that exist at the time. The wire sitting in the air stream of the intake plumbing is also sent the same voltage to begin with. However, as the air flows over it, the wire cools. (Blow into the toaster while its toasting and you will see what I mean.) The since the wire is being cooled the resistance is not changing at the same rate as the shielded wire. The computer responds by sending MORE voltage to the wire in the air stream until the voltage coming back from it matches the voltage coming back from the shielded wire. The computer then makes a determination based on the difference in the voltages being sent to the two wires to determine how much air is actually flowing into the engine.
This is why the use of oil impregnated air filters and failure to replace dirty air filters are the two primary causes of MAF sensor failure. Oil and dust will collect on the hot wire in the intake air stream and keep the air flow from affecting its resistance as it should.
However, jimbo, since you asked/alluded to this...
The mass air sensor works in conjunction with the TP and MAP sensors in MAF applications. All three sensors are employed to pinpoint volumetric changes.
MAF sensor uses a pair of heated wires (think of the heating element in your toaster) to determine the volume of air entering the engine. One wire is in the air stream while the other is shielded and only exposed to ambient air. The computer sends voltage to both wires and heats them up. The shielded wire is sent voltage and as it heats up the resistance changes and so does the voltage returning to the computer. The computer is "looking for" a specific voltage from this circuit. Once this target voltage is received, baseline has been established for the particular atmospheric conditions that exist at the time. The wire sitting in the air stream of the intake plumbing is also sent the same voltage to begin with. However, as the air flows over it, the wire cools. (Blow into the toaster while its toasting and you will see what I mean.) The since the wire is being cooled the resistance is not changing at the same rate as the shielded wire. The computer responds by sending MORE voltage to the wire in the air stream until the voltage coming back from it matches the voltage coming back from the shielded wire. The computer then makes a determination based on the difference in the voltages being sent to the two wires to determine how much air is actually flowing into the engine.
This is why the use of oil impregnated air filters and failure to replace dirty air filters are the two primary causes of MAF sensor failure. Oil and dust will collect on the hot wire in the intake air stream and keep the air flow from affecting its resistance as it should.
