Throttle Pos sensor vs. MAP/MAF

[Ric Rainbolt]

>In looking at the engine as an air flow circuit, I look at the throttle as 
>an impedance, a fairly constant pressure outside, MAP pressure inside, 
>another impedance (valves etc.), and a vacuum caused by engine at a certain 
>speed.
>
>The thing is, temperature/external pressures aside (which have to be catered 
>for anyway even when measuring air pressure/flow),
>
>For a given engine at a given speed, doesn't one throttle position map to 
>one pressure?  I understand there can be some lag; but MAP sensors aren't 
>instantaneous in reading anyway.
>
>I understand that pressure readings may harken back to the days of vacuum 
>advance in old distributors; but, temperatures aside, would a throttle to 
>RPM lookup be any different to a Pressure to RPM lookup in any situation?
>
> <snip>

To not have a MAP/MAF sensor at all would be quite interesting.  Such
changes as ring wear, valve lash, dirty air filter and barometric pressure
would throw the car off the theoretical air table.  Speed density (MAP,
Tach, TPS) systems can run without MAP in a fall back mode, though the
implementations I've seen run rougher and less fuel efficient.  The Bosch
systems I've played with (2.6) run undetectably the same with just the TPS
disconnected... strange.

Also, in this group (or was it EFI332?), there has been alot of discussion
on MAF vs. Speed-Density.  My personal preference is the latter and it
should be pointed out that the highest specific output engined car ever sold
in this country (at 162 BHP/L) used a Speed-Density system. Throttle
response was excellent and the car was able to fully meet Kalifornia
emissions laws.  Of course, it got crappy milage. :-)  The high end car
modifiers that I've dealt with all use Speed-Density, and this probably has
more to do with my descision... at least if I have problems, I can take the
car to them to get fixed.

Seems that the act of "calibrating" a MAF sensor for an application is just
as much of an effort as "mapping" an engine using Speed-Density.  Oh, well.
I'm about to find out since I'm mapping my first engine in about 3 weeks.
I'll only be getting 136 BHP/L after its all broken in, though. ;-)

Ric Rainbolt