engine/turbo theory question

[Ameer Antar]

i've tried to stay away from this topic, but I can't....I've talked to 
turbo guys and this what I've picked up...

turbo is the best type of forced induction b/c it has the lowest power 
losses, but there is a loss. Nature and engines follow the laws of physics, 
and physics says you can't get something from nothing. Power is required to 
turn the turbo, but the difference is similar to having a stock exhaust vs. 
a free-flow one. You only lose a few hp, when you put on the restricted 
exhaust, just like putting on a turbo. But the gains are tremendous, b/c 
the compressor side has big blades and can push lot's of air down the 
throat of yer engine.

turbo operating temp, is normal engine temp. no turbo manuf. will want you 
to make it glow red. Heat doesn't make a turbo work better, in fact heat is 
dangerous for turbos, as the oil [the only thing in contact w/ the 
bearings] breakdown and harden, causing the turbo to seize. You can put a 
turbo in an oven at 1000F, but it's not gonna start spinning and it will 
perform worse than a turbo at normal temp. The reason why some people 
connect heat and power is that the hotter the exhaust, the more expansion 
of the gases is occurring. In fact it is expansion, not heat is what drives 
the turbo. But again, more heat=more expansion. On the cold side, the 
opposite is occurring, the air is not expanded, but compressed. There are 
some that will torture their engine till the turbo is red hot to get every 
last drop of hp out of it. This is only for people who race and repair 
their equipment on a regular basis. I have never seen my turbo glow red and 
plan to keep it that way. Your turbo is at operating temp, as long as the 
oil is warm and lubricating the bearings...good luck...other comments welcome.

-ameer

At 12:46 PM 10/12/00, you wrote:
> >       i was discussing turbocharges with a friend - well,
> >       explaning them, actually.  he raised a question that
> >       i never thought of:
> >
> >       is there any overall power loss that comes from the
> >       pressure (backpressure?) required to turn the turbo?
>
>
>The increased pressure in the exhaust manifold over the pressure on a n/a
>car cost some power, a fraction of the power needed to drive the most
>efficient centrifugal superchargers.
>
>Super charger is driven by power that the engine has to _produce_ while the
>turbo _prevents_ the engine from producing a few hp.
>
>A properly setup turbo also produces power from just above idle, that is not
>the case with a centrifugal supercharger. The lysholm screw superchargers
>(not roots type) can produce boost at idle to maximum rpm but they need more
>power to operate.
>
>To get a turbo quick spooling the exhaust turbine has to be pretty small,
>the exhaust runners also have to be small to keep maximum exhaust energy to
>drive the turbo. The pulsing of the exhaust is important to keep, the
>exhaust pulses should 'mix' as little as possible, this is also for
>minimizing the spool up time. Remember that most turbos never reach
>operating temperature in city traffic. A turbo charger is not at operating
>temp until it glows bright red.
>
>All of these design rules adds to backpressure and prevents the engine from
>producing maximum power.
>
>For racing maximum power is more important then drivability of idle, this
>makes it possible to stretch the design rules a bit, the first measure
>usually are to make the runners and the exhaust turbine larger. By
>sacrifising the turbo spoolup when the car is not driven hard the exhaust
>backpressure can be lowered a lot, the car is still responsive when driven
>hard.
>
>
>Jorgen Karlsson
>Gothenburg, Sweden