MAF sensor and filter location

posted in: The More You Know | 0

There seems to be some debate as to how close the Euro 540i MAF (HFM, P/N 800) can be placed to the filter in a straight-through pipe. Some people seem to think that it needs a slight 2″ extension and that it will make all the difference in the world, and they base this off of… well… not very much to be honest. Catchy terms like “MAF clocking” and “Free Burritos” are used, but I will not be lured by the scent of warm tortilla holding delicious beans and rice for a nice little tasty nap to my mouth. Uh, okay, so maybe I’ve gone a little too long without eating today, the point is that MAF clocking is a completely necessary issue… if you’re using bent piping and the MAF will be situated closely to the bend, or if the sensor is not the correct size for the pipe.

Luckily for most BMW owners, the MAF you use is encased in a straight-pipe that is specifically intended and designed to regulate airflow as best as possible to the MAF; MAF clocking however is not necessary when dealing with straight through pipes, and adding two extra inches to your intake will do about nothing other than cause your headache and waste money. How am I basing these deductions? Using the power of computers and research, of course.

Let’s take a look at two different design, one with the MAF situated in nearly the same spot as it is within a 3.5″ Euro HFM (MAF; P/N 800), and the other with a slight 2″ extension between the filter and the MAF tubing.

Regular MAF:











And now the 2″ extended MAF:





Look very closely at the extended MAF, notice how the airflow around the sensor is nearly identical to that of the regular length MAF.


It turns out that the air traveling past the sensor is not only concentrated on both designs, but it is also within a 0.5% different in airflow. The cut-off for where I took the snapshots isn’t exactly the same, but with a full intake velocity of 215CFM, the MAF on the shorter pipe saw 211.4CFM whereas the MAF on the extended pipe saw 210.9CFM.

Everyone ponder about this for a while, and expect me to uphold all my personal standards when producing and creating new products for you. I will not release something that isn’t tested, researched, and modeled, and I will not curtail any values to save a buck when you deserve to get a quality product for your hard earned money.

Thanks for reading, and don’t forget to check out the E36 Euro HFM/MAF Conversion Chips (the full conversion kit will be available soon! Sorry for any delay).


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