[mwebb]

Originally Posted by AeroModder

The car they used had a MAF (Mass air flow) sensor and a turbo. My car has a MAP (Manifold absolute pressure) sensor and is naturally aspirated. Results vary.

speed density systems or
systems with Manifold Absolute Pressure MAP sensors

might actually get slightly IMPROVED FE with a clogged or restricted air filter as
MAP = Baro minus intake vacuum ,
and a restricted air filter will INCREASE intake vacuum and DECREASE the MAP value . and since MAP is the primary load sensor
AND
an increase in intake vacuum will DECREASE fuel pressure

all else the same less MAP = Less fuel injected

of course Mr 02 sensor will correct the mixture to 14.7 to 1
but
the ignition timing map will now measure with slightly less load
and too many variables to predict .

bottom line -
a clogged or restricted flow air filter WILL NOT DECREASE FE in a speed density system