Airflow metering differences

[Kracka]

Anyone feel like explaining how a hotwire MAF differs from a typical DSM/EVO MAS?

*edit* I just did a quick Google search and it looks like the common GM MAF that is used with the MAF-T setup is considered a coldwire MAF.

[Shane@DBPerformance]

DSM/Evo and some Toyotas use the Karman MAS. Those honeycombs that are in the MAS are extremely important to it working right. They create vortices that the MAS electronics count. The MAS gives out a frequency signal, which we datalog or see on an SAFC as Hz. A hotwire MAF has a wire that it tries to keep at some temperature and it figures airflow by how much voltage it takes to keep the fixed temperature. They usually put out a 0-5v signal. A 0-5v signal is much easier to work with as far as fooling things go. Some tuning systems don't even support the Karman style input/output. Nissans, Fords, Subarus, and others use 0-5v MAFs, which opens up the door for putting big MAFs on the cars from other applications, custom MAFs, and moving them into the intercooler piping or whatever.

[Kracka]

Thanks for the info Shane! How does the GM coldwire MAF differ from the hotwire?

[Super Bleeder!!]

via wikipedia:

LS1 and onwards engines (as well as others) use a "coldwire" MAF system (produced by AC Delco) where the inductance of a tiny sensor changes with the air mass flow over that sensor. The sensor is part of an oscillator circuit who's oscillation frequency changes with sensor inductance; hence the frequency is related to the amount of air (CFM) passing over the unit. This oscillating electrical signal is then fed to the car's ECU. These MAF units (such as the one pictured) have 3 pins, +, - and F, the F contains the square-wave frequency between - and F.

The mesh on the MAF is used to smooth out airflow to ensure the sensors have the best chance of a steady reading. It is not used for measuring the air flow per se and it is not recommended that you "clean" these units other than ensuring the wire-mesh is completely flat and free of any debris. Manufacturers claim that a simple but extremely reliable test to ensure correct functionality is to tap the unit with the back of a screwdriver while the car is running, and if this causes any changes in the output frequency then the unit should be discarded and an OEM replacement installed.

[Matt D.]

I split off these posts to their own thread since it was good information so the Evo X dyno thread didn't get cluttered.