[Diy_efi] RE: Banjo Dis. Pic

[Grant Beaty]

> Notice how I never mentioned wastegate.  This could be a squirrel cage
fan,
> or any system that compresses air.  PV=nRT applies universally.  If you
want
> your intake manifold air temperature to be as low as it can be in order to
> achieve maximum air density, then you treat your intake air with kid
gloves
> so as not to heat it up.

Or you get a big fooking IC :) Most people record intake temps as low as
10-20F of ambient in street conditions and a large IC, with boost pressures
as high as 28 psi. Not sure what it gets heat-soaked to on the road course
though.

I know about the compressor effeciency stuff - that was my main argument
against the idea, especially because of surge...

Grant Beaty

----- Original Message -----
From: "Brian Michalk" <michalk at awpi.com>
To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
Sent: Wednesday, January 15, 2003 4:31 PM
Subject: RE: [Diy_efi] RE: Banjo Dis. Pic


> > > Regulating either a draw through OR a blow through throttle in
> > this manner
> > > would, however, create a situation where the compressor was
> > being run at a
> > > higher pressure ratio than otherwise necessary at times, thus
> > raising the
> > > IAT, and obviously , therefore, lowering efficiency. And, in
> > the case of a
> > > blow through, pushing the compressor closer to, if not into, surge.
> >
> > Wouldn't the IAC lower as the pressure dropped across the throttle
plate?
> >
> > Grant Beaty
> >
>
> Yes, the ideal gas law applies to the pressure drop across the throttle,
but
> you have to take the throttle/compressor as a complete unit.  Making the
> compressor run at a higher ratio heats the air to a higher temperature.  A
> compressor may be 85% efficient at it's sweet spot.  Running at a higher
> pressure ratio implies more power into the compressor.  Let's assume 14psi
> goes into the throttle, and 7psi comes out of the throttle.  Let's assume
> the turbo compresses this air to 21PSI.  Say we put 10 horsepower(it's a
lot
> of air) into the compressor at this higher pressure ratio, and it's 85%
> efficient.  That means that 1.5 horsepower went into heat whipping up the
> air.  Take compressed, hot air and expand it through an expansion valve
> (thus allowing adiabatic cooling)to the ambient room pressure.  If you put
a
> temperature probe in the stream, it will read hotter than the surrounding
> air temperature because of that 1.5hp in heat, and the other unavoidable
> heat penalties.
>
> Now, assume a compressor with a wide open throttle.  Assume the room is at
> 14PSI, and after the throttle the pressure still near 14PSI.  We want a
deck
> pressure identical to above at 21 PSI, so the pressure ratio is half of
the
> above example.  Assume that the compressor is still 85% efficient and we
> only deliver five horsepower to the compressor.  The pressure ratio across
> the compressor is lower, but the MAP is the same as the first case.  .85 *
5
> horsepower now comes out to .75 horsepower that went into heat.
>
> Notice how I never mentioned wastegate.  This could be a squirrel cage
fan,
> or any system that compresses air.  PV=nRT applies universally.  If you
want
> your intake manifold air temperature to be as low as it can be in order to
> achieve maximum air density, then you treat your intake air with kid
gloves
> so as not to heat it up.
>
>
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://www.diy-efi.org/mailman/listinfo/diy_efi


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