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

[Marcell Gal]

Hi,

> >> right before the intake valve closes
> >
> > I agree with that, good point.
>
> I think I meant right before it OPENS.  If there is

naturally, before opening. Amazing how easy it is
to confirm something erraneous. I have an excuse though:
I am not a native speaker ;-)
Fortunately down in my mail I requoted correctly..
(let's hope not many people get killed because of our mistake ;-)

> The MORE difference
> bewteen ambient and MAP at a given rpm, the LESS power
> the engine is making.

nope. The less the MAP at a given rpm, the less power the
the engine is making (less airflow to it, to be exact).

The MORE difference between ambient and MAP at a given rpm,
the MORE air is flowing through the restrictions from
ambient to the manifold OR the restrictions are greater 
(throttle closed, air filter dirty).

The best simple way to think of it is the electrical analogy.
(similar model, the units differ of course)
resctriction ~ R
pressure drop ~ U
flow ~ I
We use similar model to heat transfer (used in the heat exchangers
or radiators).
The throttle is a variable resistor (potentiometer).
The air filter is a constant resistance - more or less.
The valves and head are also resistors, though
their values depend on RPM.

> And you have the big capacitor of the plenum.

yep, continuing the analogy
air container ~ C (one pin connected to ground)
long, low crosssection tube ~ L

Now you can use your favorite SPICE clone (gnucap?)
to simulate an engine ;-)

> I am working with someone who is going to be doing
> some significant datalogging, and we are going to
> outright test a lot of the ideas that have come up in

gr8. Please share the logs if possible.

> > (definitely less resource than the pure wav data
> > from a knock-sensing mic)
>
> Heh, I almost think it makes more sense to look at
> synced analog initially to get some ideas, and then
> explore the actual application of those ideas in a
> digital realm, once we know what our sampling
> parameters need to be.

The question is how can I collect those useful samples
without destroying my engine. Maybe just drive 
1 or 2 combustions to knock with advanced ign.
(or a few lost water injections at high boost etc..)
so that the engine survives the logging.

How fast does non-audible knock wear the engine?

   Marcell

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