Maximum EGT, or Turbine inlet temp, for turbocharged engines depends a lot
on the hardware that includes turbine wheel and exhaust valves as well as
valve seats. The parts I have been using in the turbo motor were Inconnel
exh valves and turbine wheel. I ultimately found that 1800 degrees f was not
damaging. My latest cyl head includes copper beryllium valve seats, which
completely replicate the materials that Roush successfully ran in the SCCA
GTO cars. My discussions with some key people both then and now reveal that
they ran up to 1800 deg f for qualifying and races with very good
reliability.
BUT we need to be very careful of the turbine wheel alloy. Inconnel wheels
can be identified by a tri lobe balance pad at the center. Part of this pad
will be of course ground off for balance. If the pad is a hexagonal shape
the material is likely GMR 235 material and will not survive at the
temperatures I have quoted. I tried and found out the hard way. As Dave D
has said in the past, we need to test enough to know how our calibration
changes will affect EGT and turbine inlet temps. In lieu of complete engine
dyno tests, chassis dynos can be helpful but temperature soaks of most
testing will not replicate BVille.
For measuring turbine inlet temp, one 1/8" type k thermocouple mounted just
before/or at the bolted turbo flange. Make the t/c tip project just a
little into the airstream as temp and velocity will/can cause a failure of
the couple and blade damage can occur. I took a nick out of one when very
early on we tried to measure temps in the center of the airflow. If you are
compelled toward absolute accuracy, use 4 t/c's, one at each side of the
runner, and average the temperatures. It might be interesting to see the
delta t. The air is just screaming thru there and I don't think many of us
understand how much turbulence is present or how the temperature varies.
For now though I'll just worry about the N/A motor and Ti valves.
Turbo is going back to work in a couple of years.....
Rick Byrnes
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