Not to butt in but...well ok, I'm butting in. He's right, Ted. But so are you
in the sense that the energy is coming from the engine either way. The
difference is that the turbo is using energy the engine generates but normally
dissipates against back pressure in the exhaust restrictions. The exhaust
system normally absorbs this energy via turbulence and friction.
The turbo ideally takes the place of this source of back pressure thereby using
previously 'wasted' energy. 'Wasted' in the sense that it was not ending up at
the wheels anyway. And seeing as how the engine needs back pressure anyway to
run right we might as well use the energy the source of back pressure is
absorbing, right?
That's very simplistic since a turbo actually does load the engine more than
normal back pressure, but the important thing is that a significant portion of a
turbo's input power does consist of this 'free' energy and a super charger's
does not.
Another way of looking at it is to think about the fact that the pistons work by
capturing the energy of the expansion of hot gases. But these gases don't
just drift out of the exhaust valve, nor are they just pushed out by the piston,
they in a real sense they are still expanding when the valve opens and literally
expand down through the exhaust system. A turbo impellor can be seen as
capturing the tail end of the expansion curve that the pistons were just going
to throw up against the static back pressure anyway.
I've heard about a related 'recapture' principle being used in some newer
vehicle(s) that use the power steering pump to drive the engine fan (saw this
posted on this list if i recall right (audi? saab?). Because the steering fluid
has to be kept up to a certain pressure at all times, the pump is always
working, but when you aren't turning the steering wheel the pressure is not
needed so it is bled back into the low pressure side of the loop; kind of like
diggin holes and filling them up again on the off chance a dire and immediate
need for a freshly dug hole arises. The fan is driven off this pressure
bleeding action. I've wondered if the same could be done with the EFI pressure
bleed of fuel.
The main waste of energy in the good old internal combustion mill is heat. It
doesn't take a rocket scientist to realize that the average set of headers puts
off more heat than a Weber Gas Grill. And
I can't remember the numbers but its an eye-opener when you first realize how
little of the stored energy in a teaspoon of gas-air mix actually gets to the
wheels. And I'm just talking normal chemical reactions here. No fission,
fusion, cold or otherwise, ha ha. Anybody remember that percentage?
Later,
Marty
TEDSDAKOTA@aol.com wrote:
> In a message dated 5/13/2000 8:59:42 AM Pacific Daylight Time,
> townsend@ainet.com writes:
>
> << Horsepower losses from a belt driven supercharger are much greater than
> from
> the impeller on the exhaust side of a turbo. I am not saying that there are
> no losses from driving a turbo, but it is much lower than a belt. >>
>
> Sho me the money ( some data )...Then I'll believe
>
> Ted O.
> 99 SLT + 4X4, 318 ci, Powerdyne SC'er, Leach headers, Gibson stainless
> catback, TransGo shift kit, R&D TB, K&N, Taylor wires, Autolite 3923's,
> 4.10's front and rear, Hoosier Drag slicks, Msd Boost retard ignition, Auto
> meter Boost gauge, Beer cooler...1.7 roller rockers...24# injectors...M1
> intake manifold, Soon electric fans, then Nitrous...
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