This is not exactly what we are looking for but there are
some clues here.

This is from SAE paper 821149 "The Effects of Turbocharger Design
and Installation on Gasoline Vehicles Transient Response" I provided
some of the instrumentation on the R&D reported in this paper.
Note the 20 HP loss in the overall steady state engine net HP out going
from a .63 to a .38 A/R. This is a T3 turbo charger. R, the radius
of the turbine, is fixed and A, the area of the nozzles, is changing.
Basically what is going on here is more back pressure and net HP loss
is being being generated by the smaller nozzle.

Just like electric motors you can get the same HP from a
turbine if you make a small one running at high RPM or a large
one running at low RPM. In this case the weight penalty is less
severe in the over all scheme of things. The larger turbine
will have the same HP loss with the same nozzle area but the
RPM will be less and the turbine torque higher. Consequently turbine
power will be nearly the same. Turbine power is the bottom line
for turbo compounding.

Paul Lamar

BTW Doug I made contact with my old friend at Garret, David Elpern (He is
still
there. Now Honeywell). See SAE paper 821149 The "Effects of Turbocharger
Design
and Installation on Gasoline Vehicles Transient Response". He is working on
gathering
HP data on the turbo chargers but don't hold your breath as that is not what
they
are really interested in. You might have to build a turbo dyno. (Not as hard
as
it sounds.)
Paul Lamar

Here is a chart from Corky Bell's book "Maximum Boost".
For a turbo compound it looks like we need the largest  A/R available for
the  TO4. Checking the 1999 Turbonetics catalog for the 13B that is 1.52
Garrett
part number 407263-0039 Tang Divided (One pipe from each exhaust port).
P-trim with a 2.544 Exducer.

For the RX8 engine with the confused side exhaust system an undivided
A/R = 1.71 should work as well. Garrett part number 407264-0039. P-trim
with a 2.544 Exducer. Big shaft in both cases.

Here too is a clarification on the A/R number. As you move around the scroll
the A/R ratio remains the same.

BTW the A/R as near as I can calculate it for the 88 89 Turbo II 13B
appears to be about .82.

Paul

Thanks for clearing up a few points. Time to search ebay. I'll test the
concept with what I have presently at hand,  the 13B.

..... So if the RX8 doesn't have a better BSFC in mid range and high range
and only gets it's increase in power from higher revs and in the high
powered version larger area of intake ports,  what advantage does it have
for turbo compounding compared to a 13B?

Doug in Japan

I don't expect much from the RX8 engine except perhaps a few hundred degrees cooler
exhaust due to slightly later exhaust port opening and the fact the exhaust is
cooled somewhat better by the cooling system. Slightly more heat lost to the cooling 
system and a little less coming out of the exhaust.

If the turbine would live the 13B peripheral exhaust is probably better
for a turbo compound or a turbo charged engine. I could be wrong. There
may be some minor advantages that will swing the balance the other way.

The main advantage of the side exhaust ports occurs down in the
idle and low power ranges of the engines. Mostly emissions.

Paul Lamar
 
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