"J K" wrote in message
. 201...
good for efficiency and engine life.

From what I've read in automotive repair histories, the
turbocharged engines require more maintenance.

J K
Turbo-charging allows an engine to pack in move air and fuel, making the
engine develop the same power as a much higher displacement naturally
aspirated engine.The energy normally wasted in the exhaust is use to pump
the incoming charge above normal atmosphere pressure. If you have more air,
you can burn more fuel. The nice thing about a turbo as compared to a blower
is that the amount of boost is related to the exhaust temperature, and this
is related to the amount of fuel you are burning. In practical terms, it
runs when you need it. The bottom line is that you can make a 300 cubic inch
engine deliver the same power as a 450 cubic inch engine under full
throttle, and run as efficiently as the 300 cubic inch engine when running
at lower power settings.

In automotive applications, the throttle lag means that the engine may take
a little longer to come to full power, and you have to use a "waste gate" to
prevent the turbo from stalling when you close the throttle quickly - like
in a gear shift. In most boating application these performance issues are
simply not an issue.

Properly maintained and used, a turbo is a very long life item. There is one
moving part - a single shaft with turbine and compressor fans. A turbo spins
a very high speeds - 60 to 80 thousand RPM is not uncommon. The bearings are
simple oil film in most cases. The oil provides both lubrication and
cooling. The cooling thing can be very important because the turbine is
driven by the exhaust. These bearings are the failure mechanism in
automotive application. These bearings have to get oil when the engine
starts up. In some engines the pressure builds rather slowly on startup. If
the engine is revved before the turbo is properly lubricated, a bearing
failure is in the cards. Another popular source of failure is during
shutdown. Frequently, the driver will roar up to a stop and shut the engine
off without letting the turbo bleed off the heat in the cooling oil. The
heat soaks through the housing; the oil left in the turbo breaks down and
cokes up the bearings. Sooner or later the one moving part of the turbo
quits moving because the bearings are gummed up.

Another common problem with turbos - if you build a big fire in a little
furnace, the little furnace burns up. An engine has to be build to withstand
the power developed during boost. A little known fact is that the old Dodge
slant six was originally built as a race engine. Richard Petty wanted and
engine built for turbo charging. If you look at one of these, you will
notice that the intake and exhaust all come together with a turbo would be
mounted. The other salient features was a very long stroke to extract all
the power generated, and *very* heavy main bearings. When there were using
in a naturally aspirated engine, they were not working very hard. The racing
rules of the day required that a certain number of the engines had to be in
productions automobiles to be allowed on the racetrack. The American public
got a great deal out of this - these engines have a well deserved reputation
as being unbreakable - they would keep running when they sounded like a
shaken fruit jar full of marbles. These engines are still being run in
industrial application like Lull lifts. The only reason they are not used in
automobiles today is that the design could not be tamed to burn fuel without
polluting. Rats.

Mark Browne