Tracy wrote "It could be argued that the exhaust energy was free anyway so
it doesn’t matter.  I don't have enough real world data to back it up but
I don't think this is true."

Back pressure rises with turbine load so you are quite right Tracy, the
energy is not free.  One of the problems that I see with venting the
compressor output is that it won't work.  Compressor maps assume that you
have more then enough power to drive the compressor.  If your compressor
is stalling at WOT you don't.

Dave, I understand your concern - you do not want to run the turbo at
150,000 rpm.  You solved that problem by putting a P trim wheel that was
designed to require a lot more exhaust gas and a bigger hot side housing
to generate shaft power.  You also improved the waste gate.  If you put a
smaller compressor up front again (not too much smaller but smaller) it
will work as desired and run at a reduced RPM.

Now if you want to try the hole in the manifold workaround, this “might”
work, I think that it has a better chance then venting to the atmosphere. Vent part of the compressor output back into the compressor inlet.  This
will force the turbo to operate at a higher rpm where it is likely a bit
more efficient.  Start with a 1/2” bypass and work up, remeber that a no
load compressor has the potential for very high rpm.  A different
compressor would still be a much better solution.

Porting the engine and building a better intake manifold could potentially
be enough to get the job done, here is a another way to do it:

In the mid 90’s I visited a fiend of mine who was the project manager on a
project yacht called Global One, it was being built to challenge the QE2
transatlantic record.  This yacht that had 2 16V92 Detroit Diesel engines
-1800HP each.  Each engine had 4 turbochargers that fed into a BIG
supercharger which blew through a HUGE air / water intercooler.  The
supercharger was needed to help the engine create sufficient exhaust
energy for the turbochargers, once the turbochargers were online and
pressurizing the intake the the supercharger was largely bypassed, the
engines where able to make more power, more boost, more rpm, the boat (90'
Aluminum) came up on plane and off you went with a 300' rooster tail
trailing along behind you.

Good Luck -- Ian
(The partial pressure experiment worked exactly as you said it would and I
hate to see you flogging this horse…)