Why MAF?

[Philip Lochner]

A general question:
 
Why are auto manufacturers so keen on using Airflow meters in their systems?  What benefits does a MAF yield to justify its presence and use?
 
 
Kind regards
Philip Lochner

Posted by email.

[jakobsladderz]

One reason is because it automatically handles any changes to the engine over its lifetime and as things wear and get changed (Eg. exhaust system changes), whereas speed-density generally does not (a better flowing exhaust system means the engine runs leaner open loop, unless the ECU can adjust based on EGO but this is not possible for all parts of the operating regime.
Secondly, mass airflow measurements do not measure eghaust gas recirc, so there is no need to compensate for egr flow rates.

As a side note, most of the bad word about airflow meters came from the early days of flap-type airflow meters that required a pressure drop to function and the hotwire type that would break a wire and suddenly stop functioning entirely. These days with the almost open tube hot film type sensors that are generally used and the slightly more restrictive but noneletheless effective karman vortex type sensors, most of these pitfalls have been overcome. An airflow meter for a given engine would be far less restrictive than a carby for that same engine.

From a DIY point of view retrofitting a MAF to a car that was not manufactured with one can be a bit tricky, due to reverse airflow due to pulsations, although some of the newer MAF's even take this into account.

MAF's are less effective on cars with very lumpy cams but then again, so is SD, that's why we have alpha-n.

Some of the V8 ferrari engines use MAF sensing (admitedly they run two, one for each bank) so it is definately used on some very potent vehicles to good effect.