Turbo Bypass

[Zack]

Ooops, Jason?!?  That flame was meant for Tom!:-)

Sorry to be a bitch about this folks, but memorizing equations and 
having insight into the physics are not the same thing.  You can't 
just look at PV = nRT in some book and start flinging it 'round and 
applying it everywhere without thinking about what's going on.
	If you want proof that Tom's explanation is wrong, just look at the 
specs for some intercoolers some time.  Cartech, for example, makes 
intercoolers for GN's with the following specs:

"The intercooler.... measures 27.5"x12"x3" and has less than 0.6 psi 
pressure drop across the core at 17 psi with an efficiency rating of 
90%"

Now, even the most spectacularly efficient turbocharger is going to 
have an outlet temperature somewhere in the vicinity of 300 degrees F
when running 17 psi of boost if the ambient air temp is 80 degrees.  
This 90% efficient intercooler will reduce that temperature back to 
102 F at it's outlet.  In absolute temperature, the inlet is at 792 
degrees Rankine and the outlet is at 594...  the absolute outlet temp 
is ~75% of the inlet temp.  Blindly apply PV=nRT to this situation, 
given that the inlet pressure (absolute) is 31.7 PSI, and you'll come 
to the conclusion that the minimum pressure drop across the 
intercooler must be 7.9 PSI.  
	That is not just a little wrong, that's -totally- wrong.  Off by a 
more than factor of ten.  QED.
	Boost pressure goes down with a better intercooler (or addition of 
an intercooler) because the density of the air charge going in the 
engine goes up, allowing the engine to pump more air through it, 
requiring a corresponding increase in the pumping capacity of the 
compressor to maintain the same manifold pressure.  The pressure drop 
is at the compressor outlet, not in the intercooler.  

Z



> Jason,
> 
> Only if volume remains constant.  Sorry, but you woulda' failed my 
> Fluid Dynamics course.
> 
> Z
> 
> 
> > As temp drops, so does pressure
> > 
> > Jason Weir wrote:
> > 
> > > ECMnut at aol.com wrote:
> > >
> > > If the intercooler doesnt create a pressure drop or act as a flow
> > > restriction why would you experience a boost drop through the
> > > intercooler?
> > >
> > > --
> > > Jason Weir
> > > 88 Wrangler - 258 Chevy TBI
> > > Fayetteville, North Carolina
> > > home.att.net/~jweir/tbi.inject.htm  --- TBI Installation Page
> > > mailto:jweir at worldnet.att.net
> > 
> > 
> > 
> > 
>