More interesting info from Vee's for Victory.
     This is supercharger HP consumption verses pressure ratio
     or
     boost looking at it another way. Allison also strangely
     plotted
     altitude on here which threw me at first. Then I realize
     they
     were talking about a flat rated engine. Constant HP as
     altitude
     increased. I think that is possible with a fixed gear
     ratio super
     charger by controlling the throttle opening.

     The several lines plotted are supercharger efficiency
     which is
     unlikely to
     exceed 80%. Never the less the bottom line is 100%
     efficiency and is a
     law
     of physics having to do with what happens when you
     compress a gas. No
     way around that.

     The left vertical axis is pounds of air per second. At a
     fuel burn
     of 10 gallons and hour you are using 60 pounds of fuel per
     hour.
     One pound per minute and .0166 pounds per second.
     At a mixture ratio of 12:1 (air to fuel) you are burning
     .2 pounds
     of air per second.

     So the chart is for 35 HP per pound of air per second at
     60% eff.
     So the supercharger HP consumed for our purposes with a
     fuel burn
     of 10 gallons an hour and a boost pressure of 1.5
     atmospheres or
     7.5 PSI would be about .2 times 35 HP or 7 HP if I am
     doing this
     right.

     10 gallons an hour fuel burn at a BSFC of .5 would be
     about 120 gross
     HP
     or 113 HP net less the supercharger HP consumed. That
     should increase
     the BSFC (fuel burn) to about .53 as I see it.

     Is this about what you are seeing Jon?

     Paul Lamar


Yeah, I think its pretty close. I'll have to check when I get to the
office tomorrow. We use an Eaton supercharger... at our max RPM and
max power, and a pressure ratio of about 1.5, Eaton publishes
supercharger power of about 20hp. That would scale down pretty close
to 7 hp at 113 bhp for the enigne (at approximately 3600 rpm). I
think we're seeing a little better BSFC at that speed / power. .53
is probably what we see at rated power. I'll have to check to be
sure.

Jon

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