Folks,
  Few bits on turbos:

  - All turbine wheels made in at least the last 30 years will be cast
  Inconel unless otherwise stated, regardless of manufacturer. No
  worries on melting stuff!

  - Most automotive turbine housings are cast iron (obviously), though
  some are made of higher temp stuff than others. The good higher temp
  ones are high sil. moly or D5 Ni-resist, assume low grade D3 for
  off-the-shelf after market. For some Garrett turbos after market
  automotive companies have made stainless turbine housings of various
  A/Rs, this is the way to go for a high duty cycle rotary IMO. Don't use
  V-bands if you can help it, they are difficult to seal and are
  expensive. Do use high temp bolts (B16 is terrific stuff!)

  - First thing to worry about when matching is the compressor, it is
  the most performance sensitive (turbines are like big paddle wheels
  compared to compressors). Special consideration will have to be taken
  for the high Pressure Ratios (PR) experienced at altitude however, so
  you're going to have to choose where you want efficiency (take-off or
  cruise)

  - Rotaries are good at spooling turbos, but don't assume they are TOO
  good when choosing a turbine A/R (you will end up with a supercharger
  like boost curve. The Hitachi turbos used on s5 RX7s do use the
  waste gate like any proper match, just after torque peak. All matching
  work is validated on engine, so expect to try a few A/Rs before getting
  it dialed in where you want (I agree with wanting a large AR for
  pressure equalizing, you will have plenty of turbine power with the
  expansion ratios you can get up there! Especially if you are not
  concerned with take off power)

  - After market waste-gates are not terribly reliable, using an
  adjustable built-in is the way to go for A/C, but a standard one may
  be difficult to keep closed at altitude unless you install a higher
  rate spring (you can build an adjustable pressure actuator with a
  turnbuckle and some clamp plates, I'll try to find a link to an
  example)

  - TEST YOUR LUBE SYSTEM!!! Make 100% sure it flows oil quickly and at
  the rate specified by the manufacturer, poor oil supply (& dirty oil)
  is a major killer of turbos. Return lines should be above the sump!

  - Water cooling is mostly chosen in non-A/C applications to prevent
  oil coking during a hot-shutdown, but I agree that it should be
  considered mandatory for a high duty cycle application (with tight
  packaging). Return lines should be as high as possible in the cooling
  system to aide thermal siphoning

  - Typically ball bearings are only chosen when transient performance
  is crucial, as journal bearings will get you 80% of the performance
  with better steady state efficiency, but ball bearings are better with
  low oil conditions and can handle higher loads. IMO unless you have
  the $$ burning a hole in your pocket standard bearings will do just
  fine, and they have MANY more hours of design history behind them.
  (eg. To my knowledge no production engine uses a ball bearing turbo
  except the Garrett on the new Ford Scorpion engine.)

  I saw someone ask about cooling system additives. Redline Water Wetter
  is well thought of.
  FWIW unused oil has a thermal conductivity of around 0.1 W/(m-K),
  water is around 0.6, ethylene glycol around 0.2

  Cheers,
  Zach K
  Guy that works in the industry

  Thanks Zach. Some of the best info we have received so far.

  Paul Lamar

  Thanks Zach,

  I learned a few new things. What part of the industry are you involved in?

  Doug in Japan


  No problem, turbos are a tricky device and real information is very
  sparse in the aftermarket world.

  Fundamentals of Turbocharging by Dr. Nicholas C. Baines is an
  excellent text for turbo knowledge.
  http://www.conceptsnrec.com/Education/Engineering-Textbooks.aspx

  Near the bottom of the page is a picture of an actuator with
  replaceable spring where the 2 halves of the actuator are held together
  using clamp-plates.
  http://powerenterpriseusa.net/products/turbo/list_spec/index.htm

  I do applications and development for a turbo OEM.

  Cheers,
  Zach


 Zach,

 Is there significant performance difference from a TE04E turbine
 housing with a tangential inlet compared to a more centrally located inlet?
 In the size I want, the tangential turbine is not offered with
 a split inlet, however the central housing is.  The central
 housing (like the old Raja turbines) has some advantages to get a close fit.
 The sales rep. says I can order the unit with Inconel shaft and
 turbine (extra) as well as ceramic bearings.    I am considering
 P trim and 1:15 turbine AR,  Compressor 50 which  I assume is
 the nominal size.   Not sure which size turbine to get.  Several options.

 Housing unfortunately is ductile cast iron and having the housing
 cast in Ni resist  may not be possible.  Only a few of the GT 28
 series used that alloy.  E-85 will help cool the inlet charge as
 well as a log type exhaust manifold.   Good news is this size of
 turbine is in the 15lb range.
 External waste gate is   necessary.

 Doug in Japan

 http://tinyurl.com/26zwdgf

Doug,
The tangential inlet will provide slightly better performance, more so
with a pulse tuned exahust, as opposed to constant pressure method
which would be less sensitive to center/tangential (peripheral exhaust
rotaries are so perfect for pulse tuned turbocharging it's like Dr.
Wankel and Mazda intended it). Though as you have found central inlet
is often easier to package.
In the end, being able to properly match the turbo is MUCH more
important than tangential/center, twin-entry/single entry. Choose the
option that gives you the AR you want first, the other stuff is fine
tuning. Even with a single entry turbine it would still be worthwhile
to design the manifold such that the turbine inlet runners are equal
length and blend together nicely. (w/ as small an manifold volume as
possible).

Lower grade cast iron will work, it just may not last as long before
cracking, and not allow as of high turbine inlet temps, steady state,
before creep becomes a worry (TIT, thermal cycles, vibration,
mechanical loading and time are the levers for durability outside of
turbine housing design). IMO aircraft turbos should be Magnafluxed &
inspected as often as an exhaust (will need to torn down to properly
inspect the turbine). The place cracks usually first appear is in the
tongue of the volute. (see attachment, not my image) The divider
between volutes in a twin entry is also one to inspect.

Without running numbers the 1.15 you mentions sounds in the ballpark
(perhaps even larger at altitude), though AR is also very dependent on
the turbine. Hot side matching is still as much an art as science, and
typically requires a couple iterations to get things right where you
want. (less so if you have VGT) Aircraft would seem to be a bit easier
if you are mostly concerned with cruise (1 operating point), and in
the aftermarket you really only have AR as a lever for tuning.

I am surprised by them not having Inconel turbine wheels standard. The
turbine should be Inconel and the shaft some other steel, do they mean
the "upgraded" option also has an Inconel shaft? That is unnecessary.
Though if the aftermarket turbines are not Inconel the extra cost is
worth it for many reasons (the only reason not to have it Inconel is
cost).

http://www.tialsport.com
Is a good quality source of aftermarket turbo bits for Garrett (they
even have water cooled wastegates! Durability enhancer).
http://www.turblown.net/home.html
Are fabricators of fantastic quality (the cost reflects this)
made-to-design tubular manifolds, and rotary savvy, ask for Elliot.
From my memory they also have an ex-Garrett engineer that consults.

FWIW, I don't work for Honeywell but they have the most options for aftermarket.
Also, apologies for the long winded response, there is a lot to consider.

Cheers,
Zach