Air Flow Measurement

[Mazda Ebrahimi]

RABBITT_Andrew at mv8.orbeng.com.au wrote:

> 
> I've never played with a speed-density system, but from what I've
> picked up in the industry, the following brief thoughts may help:
> 
>  - MAP is cheap
>  - MAP is calculated from several measurements, therefore the errors
> accumulate during calculations, whereas MAF is measured directly.
> It's debatable (I think) whether MAF is superior in this respect since
> temperature and MAP are easier to measure.
>  - MAF requires manifold filling compensation, where MAP doesn't

This can be an advantage or disadvantage depending on type of fuel 
delivery systems.  Most production cars use MAF with port injection, but 
I think it is more suited to throttle body setups.  With TBI, you want 
to inject the fuel with the air at the throttle body, so no manifold 
filling compensation is needed.  So I think MAF would be a little easier 
to calibrate with TBI.  The reverse applies to MAP and TBI, where the 
MAP sensor doesn't sense the in rush of air immediately, therefore more 
accel (TPS) transient enrichment is needed.

>  - MAP can't handle EGR since this increases the MAP without an
> increase in airflow
>  - MAP relies on VE data which must be measured and which changes over
> the life of a engine, and from engine to engine.  This can be
> corrected though using closed-loop adaption/learning techniques.
> 
> I think if you look around, there are enough cars around still using
> speed density systems to prove it's still a viable technology.  In
> industry, most things are set up on an engine dynamometer, so
> measuring what you need (MAF or MAP) is not a problem.  For the DIY,
> it's a different kettle of fish.
> 
> If I were doing it DIY (one day!) I would use MAP and adaptive
> learning of VE and force the engine to learn it's VE map at the
> appropriate resolution by carefully driving the car around.  Then I'd
> calibrate the open-loop areas (mainly WOT).
> 
> Andrew Rabbitt

Thanks Andrew for your input on the flow reversion stuff as well.  I 
will be flow bench testing a MAF sensor (0 to 5 volt dc output) and post 
the results next week.