I did an experiment today to see what effect back pressure from a turbine
housing has on performance.  My engine is currently set up using an empty
stock turbine housing as my manifold/muffler.  First I ran the engine with
the housing and exhaust pipe in place, then I removed the housing and ran it
with just the manifold in place.  Here are the results given in static RPM:

                          MAP 20     MAP 25   MAP 28.5 (WOT)
With Turbine Housing      2700        3350      4700
With Manifold only        2790        3450      4790


The sound was notably louder without the housing (neighbor came out to see
what was going on), but not as much of a difference as I was expecting.

These results have convinced me to stick with a turbo (not as much detriment
from back pressure as I thought), still working on the installing the TO4B,
but it probably won't be done until the Fall (working too hard, and I don't
want to interrupt my IFR training schedule).

Dave Leonard