Turbocharger surge speed...

[MaxBoost at aol.com]

As I understand it, it is basically the fact that the turbo is trying to
force more air into the engine than the engine can consume at that given
moment based on rpm and volumetric efficency.  When this happens the air is
forced backwards through the compressor, which causes shaft whip, increased
exhaust backpressure and will try to spin the compressor nut off if it is
right hand thread.  In severe cases it can cause the compressor wheel to tag
the housing, in mild cases it shortens the life of the thrust bearing.

If you run a compressor into mild surge, its probably not a big deal.  This
usually occurs when trying to run a big compressor on a small engine at high
boost at low engine rpm.  If the turbine is sized correctly, then the turbo
will never make enough boost at low speed to drive the compressor into surge.
 This is how all the cars in the magazines these days get away with running
huge turbos on small engines.

In my case I have a 3.0 engine with a T-51 compressor and a T-4 turbine,
years ago this was unheard of, but now days its no big deal.  It is slightly
laggier than stock, but will make alot of boost and consequently power at the
higher rpms.  Testing has show its making in the neighborhood of 450 hp at 20
psi boost on a basically stock motor with the appropriate intercooler and
fueling.

Max