[Diy_efi] Magesquirt vs D- jetronic

[Adam Wade]

--- John Nevius <jnevius at spiritone.com> wrote:

> It can operate as a true mass flow system (it knows
> the amount of O2 being sucked into the engine by
> knowing the temperature of the intake charge and its
> absolute pressure)

It's my understanding that MS operates as a
speed-density system, which is what you described. 
Mass airflow requires a hot film or hot wire sensor,
as I understand it.  I don't believe there are any
home-brew MAF systems out there, although I suppose
there is no reason you could not write code for the MS
that would allow use of a MAF sensor.  Initial
calibration would be a bit of a bear, I'd guess.  And
MAF sensors are quite costly...

> Mass flow is normally better, however engines with a
> high cam overlap sometimes produce erratic vacuum
> readings.

MAF is more accurate EXCEPT when speaking about
transitory airflow after rapid changes in alpha. 
"Better" is sort of vague.

> There are variants available that allow
> you to run alpha-N at low RPMs and mass flow at
> higher RPMs.  

Again, ITYM speed density rather than MAF.  There
would be no reason to use alpha n main metering if you
had a MAF sensor, unless you were running a big cam;
I'd recommend a straight alpha-n system for really
lumpy cams.

> Throttle position can be used with mass flow to
> simulate an accelerator pump on a carb'd car
> (momentarily increase the squirt when the throttle
> is opened).

In fact, it's required if you want the vehicle to be
drivable.  All systems of which I am aware use an
"accelerator pump" feature for transitory airflow
after large/sudden changes in alpha.

> and intake air temperature (for the mass flow
> calculation).

MAF is measured, not calculated, and a MAF sensor has
built-in temperature calibration for the resistive
elements.  Speed density requires AAP and AAT to
determine density mathematically.

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