MAP and TPS LOAD based EFI

[John Dammeyer]

Hi all,

In my opinion the answer is yes.

There are a number of methods for measuring gas flow.  Hot wire flow meters
that measure the cooling of an element in the gas stream.  Turbines.  A
really neat one is to us an LDV;  Laser Doppler Velocimeter.  Another method
for measuring flow of gases in the oil industry is to use a differential
pressure gauge and a restriction in the pipe.  If you know the diameter of
the restriction and the temperature of the gas,  you can calculate the flow
rate from the difference in pressure.

The absolute pressure value inside the restriction isn't important;  it's
the difference between the two.  Looking at an engine we see much the same
problem.   What's really more important is how much air can we move into the
cylinder within the time that the intake valve is open.  If the pressure
outside the intake manifold is half of sea level atmospheric -- say 15" and
the MAP sensor reads 15" at 70F then your airflow is 0 CFM.  In reality the
MAP will always read a little more vacuum than the ambient so it may ready
14.5" but in either case,  airflow is very slow.  Compare this to 29.92"
atmospheric and 14.5" inside and you know you are sending air into the
engine.

Now you can get away without a barometric pressure sensor and a 2D table
RPM-MAP but it won't handle a trip to the mountains as well as one that
corrects for altitude.

IMHO

Cheers,

John


----- Original Message -----
From: "Tony Bryant" <brd at paradise.net.nz>
To: <diy_efi at diy-efi.org>
Sent: Saturday, January 13, 2001 5:48 PM
Subject: Re: MAP and TPS LOAD based EFI


> I have a question:
>
> Everybody knows that  as a first approximation a certain MAP & RPM will
> give a constant fueling pulse length (assuming tempertature(s) are
> constant).
>
> Everybody also knows that you need transient enrichment.
>
> Now the question is. Is it possible to get two steady state situations in
> which
> the MAP, RPM, IAT are the same,but the air flow through the engine is
> significantly different?
>
>
>
>
>
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