The Facts about Mass Air Flow Meters

Size Does Matter!

If you have an engine that makes enough horsepower to warrant larger injectors, you will need to complement it with a Mass Air Flow (MAF) meter that is not only properly sized, but properly calibrated as well. If the MAF meter is not large enough, it will become a restriction in the intake path and will limit the engine's overall horsepower potential. If the meter is too large, it can loose resolution, and accuracy. You should choose a meter that is sized appropriately. Of course, we can help you make the proper decision. Below is a list you will find helpful.

Calibration

The MAF meter's calibration is equally important. In fact, having a properly calibrated mass air meter is the single most important factor that should be considered when choosing an aftermarket MAF meter. The meter should be calibrated to match the flow rating of the fuel injectors, in conjunction with the PCM (engine computer) being used for the given application. A properly calibrated MAF meter will result in a meter that generates an accurate voltage signal vs. the air mass entering the engine throughout the entire RPM range of the engine. If the meter you are using is not properly calibrated, the meter may "peg" (reach maximum voltage output) before the engine reaches maximum airflow, which will result in an inaccurate air/fuel ratio, causing a loss in horsepower, or even potential engine damage. In contrast, it may fall below the PCM's expected minimum voltage input at idle speed, which will result in the PCM entering a "failure mode", which will cause a very rich condition at idle. A properly calibrated MAF meter ensures that the PCM receives a correct signal throughout the engine's entire operating range, resulting in a proper air/fuel mixture, maximum horsepower, excellent drivability, and maximum fuel economy.

There are various methods currently being used in the aftermarket to recalibrate MAF meters. There is only ONE correct method. These methods are as follows:

One method being used manipulates the voltage signal from the MAF meter by mechanically changing the amount of air that is permitted to pass by the filament of the meter. This is done by installing a different size sampling tube, or by restricting the flow through the tube with a screw. While this method can result in a voltage vs. air mass reading that is usable by the PCM, it is not possible for it to be correct throughout the entire RPM range. This WILL result in some form of drivability concern. These are commonly reflected as idle problems, loss of power, and poor drivability & fuel economy. Expensive and time consuming dyno time is highly recommended with this type of meter, and the results are not always consistent.

There is also a method of introducing a "MAF Tuner", which is usually some type of in-line electronic device which is intended to vary the voltage output of the mass air meter to extend the range or allow the use of a MAF meter that has not been properly calibrated. These devices will require dyno tuning to work properly, because the MAF "curve" does not match that of your PCM. Since no transfer function information is available when using these devices, expensive and time consuming dyno time is an absolute must!

There is also the option of using a meter that has not been calibrated at all, or is not properly calibrated. See "Buyer Beware" below. Commonly, these meters have a generic curve that may, or may not operate within the appropriate range of the engine. These meters will require dyno tuning to work properly, because the MAF "curve" does not match that of your PCM. Since no transfer function information is available when using these meters, expensive and time consuming dyno time is an absolute must!

The final, and BEST, method for calibrating a MAF meter is to change the MAF meter's voltage output by manipulating the electronics of the meter itself. This is an extremely accurate way to calibrate a meter because the meter's "curve" can be precisely targeted to reflect the needs of the new application. Pro-M Racing was pioneered in 1988 by Bob Atwood, a Ford engineer who was instrumental in developing mass air technology. Not only is this method based upon OEM techniques, this is truly the ONLY way to PROPERLY calibrate a mass air meter. Pro-M is the only aftermarket company with both the intellectual and physical properties necessary to properly calibrate your mass air meter. In order to properly calibrate a meter, you need to know the baseline "curve" of that meter. Quite simply, we are the only aftermarket company in possession of this information.

As an added bonus, All Pro-M meters are supplied with a transfer function sheet. This is the air mass vs. voltage data for your particular mass air flow meter. This is invaluable information for anyone who desires to have their PCM professionally tuned. It allows the tuner to have the EXACT air mass vs. voltage data for your meter, resulting in a perfectly accurate reading by your PCM. No other method of calibration will provide you with this important information. Lack of this information will result in a "tune" that is, at best, an educated guess.

Buyer Beware !

Some people will say anything to get you to buy their products. These people will very carefully word their advertising to mislead you into thinking they are able to calibrate a meter to suit your needs. Make sure you educate yourself about their abilities before you buy! This is actually quite easy to do. Ask them to recalibrate your existing meter. If they can't, or if they say they can, but won't do it for you, then they are not calibrating their own meters. These people are selling meters with generic curves. They will require dyno time.

Repeatability Vs. Accuracy

If you have ever been MAF meter shopping, you have likely heard the term "repeatability". Repeatability simply refers to how close one meter's calibration is to the next one. In other words, if you had a batch of 100 MAF meters, could you substitute any one of these meters for any of the others and have the same result? If you can, then the meters are "repeatable".

However, repeatability is often confused with accuracy. Accuracy refers to how close the meter's calibration is to the required calibration. Those same 100 meters could be 100% repeatable, and still be very inaccurate. It is much more important for a meter to be accurate, than it is for it to be repeatable. When you have accuracy, you have repeatability. However, when you have repeatability, you do not always have accuracy.

At Pro-M Racing, we individually calibrate our meters to be extremely accurate, AND repeatable. It's all in the calibration. We base our calibrations on the original OEM manufacturer's baseline specifications. NO OTHER aftermarket MAF meter manufacturer is able to make this claim! Other companies compare their calibrations to actual production MAF meters, which typically have a tolerance of (+ or -) 4 to 6%. When you add this to other manufacturers accepted method of recalibrating MAF meters, you could potentially end up with a meter that is as much as 10 to 15% off the desired target, and yet still checks out fine by their standards. All PRO-M MAF meters are held to within (+ or -) 2% of the original manufacturer's specification - This is a tighter tolerance than is even available with an OEM MAF meter!! Our most popular meters, the "Pro-M 80 and Pro-M 92", can actually hold a tolerance as close as 1%. Quite simply, our combined experience and manufacturing methods insure that you will get the best MAF meter that your money can buy. No one else even comes close.