Variable Compression, Variable Displacement you decide

[Tony Cooper]

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. 

> 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...

> 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...

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

-- 
Sent By Tony Cooper.
email: tony.cooper at virgin.net
Allow at least 10 working minutes for reply. ;)