Variable Compression, Variable Displacement you decide

Roger Heflin rah at horizon.hit.net
Wed Feb 18 13:27:59 GMT 1998


> 
> Roger Heflin wrote:
> 
> > I will disagree what what you said.  Having seen a small engine with large
> > boost compared to a large engine, the engines have vastly different
> > torque corves, therefore they aren't equivalent.
> 
> True.
> 
> > Also the number of
> > compression stages and the number of expansions stages has nothing
> > to do with the efficiency.  Thermodynamics says more stages don't
> > increase efficiency.  The reason a supercharge is generally
> > less efficient is that they compress more air than is needed, and substantially
> > increase the pressure in the intake more than is necessary.  If there
> 
> False. 
> 
You say false.  Lets hear your argument and reasons.  And why anyone
should believe your false.


> > were a way to make the boost constant over rpm things would be better.
> > The way a turbo handles this is when a certain pressure is reached
> > some of the exhaust bypasses the turbo keeping the pressure lower.  This
> > allows a turbo to have high boost at lower rpm where a superchargers
> > boost curve goes up with rpm until at close to redline it is at
> > close to the detonation limit.  With real world examples if you look
> > both a turbo and super engines, same displacement, and same boost
> > makes close to the same peak power.  The curves are somewhat different
> > because of the boost characteristics of each, but fuel efficiency
> > is very close.   
> 
> Very false...
> 
Again same as above.  The auto books I have read say the biggest problem
with a supercharger is how much power the use at high rpms.  This they
say is the only disadvantage of a supercharger over a turbo.

> > The power the turbo uses is not free.  If a super
> > engine dumps its exaust at x psi into the exhaust, and the turbo
> > dumps it at the same x psi into the exhaust (after the turbo), they
> > can have the same efficiency if they are both designed correctly.
> > 
> 
> Sorry, but that last bit is pure rubbish as well...
> 
Again why is it rubbish?  Because you say so?  Lets hear reasons.  If
it was rubbish there should be not production superchargers in vehicles
requiring fuel efficiency, yet there are so the above statement most
almost certainly be true.   Lets hear your reasons...


> I am sorry to be so curt, but have had flu since Sat morn, can still
> only just walk - will reply in MUCH detailt when I can type again.
> Tony

For that matter, lets hear what training allows you to be such an 
"expert".  

Sorry to be so curt.

			Roger



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