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Date: Mon, 26 Sep 2011 09:15:05 -0500
From: Dave <david.staten@gmail.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Boost
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On 9/26/2011 9:02 AM, stevei@carey.asn.au wrote:
> Hi Guys
> Could you educate me here.
>
> Q1. If Dave is boosting to 45"Hg then am I right that that is ~22psi.(now I take it that is referenced to static at whatever altitude Dave quoted)
  45" mmHg ~ 22 PSI... if both have a common zero point.. I dont do 
cars, so I dont know what the motorheads use for zero - ambient or true 
vacuum. But your numbers are correct presuming 0" = 0 psi.


>
> Q2. Now lets say a 13B with a wonderful intake has 100%VE and makes x horsepower at 6K RPM.
> If we boost that same 13B at 14.7psi after a really nice intercooler and spray bar that drops the temp to ambient (hypothetically speaking).
> Will this then double the charge mass and therefore the potential energy and so produce 2x horsepower at 6K RPM?
If you increase the intake charge pressure from 14.7 psi/30" mmHg 
(ambient sea level pressure) and double it to almost 30 psi/60" mmhg, 
(and for theory sake, have a hypothetically perfect intake and 
intercooler, with no losses) and add fuel proportional to the mass of 
the air (which in this case is doubled) then your HP would be 2x.  You 
seem to grasp the academic concept.

Now.. reality check time....
And you will make twice as much heat that needs to be rejected out of 
the cooling system, but twice the hp wont give you twice the speed. 
Twice the fuel cost - at a minimum... you likely will have to run rich 
to avoid detonation in a real world installation, and intake charge 
temps may be close to 200 degrees after the intercooler. Drag increases 
in an exponential fashion, so you will make twice as much heat (linear), 
generate more power (linear), Generate more drag (logarithmic), and get 
decreasing amounts of speed for every increased unit of power generated 
(negative logarithm)


>
> If this is really dumb thinking. My apologies.
> I deeply appreciate the great minds and practice on this list.
>
> Cheers
>
> Steve Izett

Dave