Re: S.P.E.A.R.C.O.intercooler guys?? -Reply

[Robert Myers <rmyers@inetone.net>]

Gross,

I'd wager that your turbo is able to provide about all the compressed air
your car can use.  Better cooling might be the way to get more power more
effectively.  

A different turbo might, however, spool up more quickly and produce
significant boost sooner than the existing turbo.  This is definitely a
consideration.

You also need to be concerned about running excessively lean at max boost.
If your turbo/IC is capable of providing more air than the fuel system is
able to provide fuel for then your combustion temperatures will be elevated
and you will be in danger of burning metal where you should ought to be
burning metal (valves, cylinders, etc.).

Really, Gross, the effects of pressure and temperature (absolute not F or
C) are pretty much equal (but opposite directions, of course)  A 10%
increase in absolute pressure will have about the same effect as a 10%
decrease in absolute temperature.  The sticking point is that a 10%
decrease in absolute temperature is a lot larger temperature change than
most people commonly would think.  It must be the absolute temperature that
is considered.  

As an example, a 10% decrease in temperature for air at 150 degrees
Fahrenheit would be a 61 degree drop not a 15 degree drop.  You'd have to
cool the air charge from 150F to 89F to get the same effect as increasing
the boost from 8 pounds of boost to 10.3 pounds of boost.

I didn't show the math here but I converted deg F to the Rankin scale and
treated the absolute manifold pressure as one standard atmosphere (14.7
psia) plus the boost figures.

At 10:49 AM 6/16/97 -0700, you wrote:
>Bob,  very informative post!  Excellent point about temperature scales,
absolute
>vs relative and their relative heat content... easy to overlook those
things. 
>Long dormant synapses came to life while reading it... those classes were
a long
>time ago.
>
>For the purposes of this list, however, there is one critical relationship
that
>remains unsaid.  Your derivation left me with the impression that pressure
and
>temperature have equal, although opposite, influences on density.  As I
recall
>their influences are not equal.  
>
>For instance, for long range effeciency aircraft need to fly in the least
dense
>air mass they can reach.  Usually this is around 34-37k feet where the
>tropopause occurs.  Air mass temperature decreases from a high at sea
level to
>the tropopause where it stays essentially constant into exoatmospheric
space. 
>Pressure, however, decreases from a high at sea level to a low some numerous
>miles in space, well above the tropopause.  Apparently temperature has a
greater
>effect on density than does pressure.
>
>If one has to address a trade off in a turbo/intercooler application, ie,
do you
>go for more pressure or more cool, which way is most productive?  I
realize this
>is not quite an apples-to-apples swap in terms of efficiency and cost, but
which
>factor has the greatest influence?
>
>Do I spend my money on a bigger turbo, or do I try to find better ways to
cool
>the air mass that I've already compressed?
>
>Again, excellent info!
>
>Regards, Gross
>
>
>
>
___
   Bob
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