[Diy_efi] Speed-density vs. MAF/MAP...

[Marcell Gal]

Hi Adam,

(I reroute the discussion to the list if you don't mind)
> In addition, you can read MAP before or after the
> throttle.  That would give two very different numbers.

you're probably right. However since MAP is 
Manifold Air Pressure I would not call 
pre-throttle Air Pressure as MAP. That is confusing, I think.
(wether it is in practice or not)

> If you read MAP from the throttled volume

that's what I call MAP

> right before the intake valve closes

I agree with that, good point.

> That all makes perfect sense to me.  If you have a
> higher throttled volume MAP before the intake valve
> opens, at a given RPM and throttle opening, then
> you're going to get better filling.  If the engine
> itself suddenly becomes more efficient (tuning the
> exhaust to that particular RPM, for example), then the
> MAP should drop slightly as more air moves through.

OK. So we can confirm the appr. 
VE= Constant * (pAmbient - MAP)/RPM
relationship, 
( only applies, when MAP(RPM) is measured at WOT,
seems similar to an airbox pressure sensor config)
which is quite inverse of what could be thought
or some previous email suggested (though not stated explicitely).

> I'm led to wonder, since the most obviously useful MAP
> numbers seem to come from the throttled volume, what
> the real-world difference is in plenum MAP and
> throttled volume MAP.  

Is there a better name for Plenum Air Pressure, like PAP?

> Does the plenum and throttle(s)
> act as a filter for low-rpm pulsation to some degree?

I think so. The further away from the valves, the smoother 
the airflow should be -- generally. Especially before 
a restriction, like throttles. 
Why don't we take 32..64 MAP samples
per revolution? (at least to get datalogs to support the 
pre-intakevalve-opening theory).
Even processing that realtime should not be too prohibitive 
with fixed point math. 
(definitely less resource than the pure wav data from a knock-sensing mic)

  Marcell



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