MAF and SD (was re: Re: New member intro)

[tsakiris at ed8200.ped.pto.ford.com]

>>GM speed density uses only MAP.  Did Ford's aborted attempt at speed
>>density use a BAP sensor?  (the worst comments I've heard about that
>>system have all come from Dearborn :)
>>-- 
>>Jonathan R. Lusky                        lusky at knuth.mtsu.edu


>*ALL* SD systems require a barometric pressure reading.  On GM, Ford, etc.
>the reading is taken under two conditions:  (1) engine cranking (when MAP is
>close to BP) and (2) close to WOT.  Early (GM) CCC systems for carbureted
>engines also used a "baro" sensor.  The baro sensor is nothing more than a MAP
>and BP sensors with an analog subtraction circuit to output the difference of
>the two.  The really early stuff used separate BP and MAP sensors (made by
>Bendix).
>
>I'm not so certain that Ford's "attempt" at SD controls is "aborted";  almost
>ALL the Ford stuff that's rolling on the roads is SD and it certainly appears
>to be functioning properly.
>
>Regards,
>
>Bohdan Bodnar


Good points.  For unrelated reasons (I used to work on superchargers), I was
thinking primarily of a boosted engine.  I believe it had a BP sensor in 
addition to a mass air flow sensor.

Just a few more quick comments:

'Functioning properly' is becoming less perceptible to the driver and more
a matter of passing Federal certification tests.  The tests may or may not
represent the desires of the buying public, but that discussion is a 
philosophical one.

With regard to speed-density vs. mass air flow, has anyone considered the 
robustness (not in a control sense) of the two systems to errors such as 
air leaks and sources of inflow downstream of the throttlebody?  Is a 
speed-density system more resistant to or accepting of such disturbances?

Tony