MAP Sensors

MAP is an acronym for Manifold Absolute Pressure.  The MAP sensor is a key component in a Speed Density fuel injection system, and measures pressure and absence of pressure (vacuum) at the intake manifold.  MAP sensors typically have 3 wires: a 5 volt reference signal wire, a ground wire, and the wire that goes back to the ECU for all that sweet, sweet air related data.  The ECU (a.k.a PCM, ECM) then calculates the air / fuel ratio based on VE tables within the computer. We will cover Volumetric Efficiency tables at a later date.  Just imagine a magical grid in the computer that says “if you see this voltage from the MAP, then do this…”.  The cool thing about these sensors is that they are simple, and can be easily used for higher performance applications.   The bad thing about these sensors is that they are part of the speed density fuel injection system that doesn’t know exact amounts of air going into the engine, it just makes educated guesses at it.   These guesses are all well and good, but solid numbers are always better.  Or are they?  Naturally, there is much more to a speed density fuel injection system than just a MAP sensor…..

IAT Sensors

IAT is an acronym for Intake Air Temperature.  The IAT sensor measures the air temperature that is going into your intake manifold.  The colder the air, the more dense it is, and the more fuel you need to keep your engine happy.  Coool ….literally.  Almost all IAT’s are simple two wire devices that measure resistance.  As the air temperature changes, the resistance in the sensor changes and the ECU knows to change the A/F ratio based on this.  Combine this data with that of the MAP sensor and your computer can now give a pretty accurate guess of the volume of air moving through your engine.  This is great news, but it’s all based on calculations, instead of real solid numbers.  This is where speed density is tossed aside and big Mr. MAF enters the party…..

MAF Sensors

MAF is an acronym for Mass Air Flow.  These sensors are pretty impressive because they measure air volume, along with temperature, all in one (no IAT necessary!).  Remember, the MAP sensor above measured intake manifold pressure / vacuum and then estimated air volume with computer software.  A MAF actually measures real air volume so that the computer doesn’t need to guess what it might be.  As you can imagine, MAF’s are typically more accurate ways of measuring the amount of air that goes into your engine.  This sounds great, right? Well…. it is, on a stock vehicle, and even lightly modified ones.  However, if you decide that you want to make way more horsepower than your car was ever intended for (where do I sign?), then MAF just isn’t going to cut it.  MAF’s quickly become bottlenecks in your air intake system because they can only measure “X” air at once.  If your engine needs more than “X” amount of air, then your MAF freaks out causing your engine to run lean and quickly turns rotating engine parts into liquid hot magma, (Hellooo magma).  This is where Speed Density is welcomed back into the party, and brings along a couple of lovely friends, known as MAP and IAT.

So as you can see, there are pros and cons to each, and it really depends on your vehicle and its modifications to choose who is the cooler sensor at the engine party.  Luckily, choosing one or the other only needs to happen when you modify your car to the extreme.  If you have a stock car, none of this really even matters.

For those of you that are attempting to make crazy horsepower,  what do you guys & gals prefer?

2 comments to MAP & IAT vs. MAF

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