>      Did you have any small leaks in the turbo intake manifold that you know
     >      about? Unlikely but that would increase the turbine RPM. Also if the compressor
     >      is undersize for the amount of engine combustion air required that too will
     >      drastically increase the turbine RPM.
     >
     >      As I said however I don't believe this is the root cause of failure.
     >
     >      Paul Lamar

     > Tracy Crook wrote:
     >      Not a significant factor in this discussion but for the discussion of any centrifugal pump (air, water, whatever) it should be remembered that the load on the pump increases with
     mass
     >      flow.  In other words, the turbo would slow down if there were a leak in the intake manifold down stream of the turbo.  Load on a centrifugal pump is at minimum when the
     backpressure is
     >      highest.  Sounds counter-intuitive, but true.
     >
     >      Tracy Crook

     I do agree that a high back pressure on the compressor such as a closed throttle would cause the
     the turbo to speed up if the HP going into the turbine was constant.

     BUT why would the back pressure be higher with a leak. I think it would be lower.
     The turbo might slow down because the turbine is getting less HP because the boost is down.
     We are working with a complex closed loop system here. Less intake pressure less HP. Less HP lower
     engine RPM. Less engine RPM less requirement for combustion air.

     Paul Lamar
     I don't know how you find the time to do the newsletter (but thanks!) but read my post a little slower.  I didn't say backpressure would be higher with a leak, I said the turbine
     speed would slow down (because of the higher mass flow) and LESS back pressure.  This was of course ignoring the factor of engine power and exhaust flow which would also go down causing an
     even further reduction in turbine speed.

     Main point is that all other factors being the same, load on a centrifugal pump goes higher with less back pressure.  Again, it's counterintuitive.

     Tracy Crook

You did say:

"Load on a centrifugal pump is at minimum when the back pressure is highest."

What you say would true  in the turbocharger case if it were not for the fact 
that the air requirement of an engine increases with the increase in engine RPM. 
At a given engine RPM if there is a leak in the intake manifold there will be 
less boost pressure and less engine HP to drive the compressor. Things are not  
simple in a turbocharged engine.

I am spending a lot of time on the newsletter because I decided to quit
commuting 65 miles each day to the hangar. I finally got she who must be obeyed
to agree to move much closer to the hangar this coming spring. I will then be able to
spend more time on building my airplane and getting my NC mill up and running. 

How is the flood going? Is the water finally going down? I'll be in Florida
next week for a few days and will try to get up to Lake City.
  
Paul Lamar
 
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