Eric,

A number of comments to your long post.

I said:
<< ... a TIO-540 has a BSFC min of around 0.415, NOT .59.

...a BSFC as low as 0.385 which is typical of a 300 HP IO-550. >>

You said:

>>Well, we have to separate flying fact from engine company fiction here.<<

To which I respond:

Yes.  But we also have to keep in mind the hard science of thermodynamics.
The fuel that is excess to the BSFC(min) fuel flow is not "inefficiency"
that contributes to increased heat rejection into the cooling system.  It is
just excess fuel that ends up going out the exhaust system as unburned  CO
(carbon monoxide) (primarily) rather than CO2 (CO that is further oxidized
to CO2).  The measure of the fundamental Carnot efficiency that is at issue
in your heat-rejection argument must - - to have any validity  - - use the
BSFCmin as the starting point.  

So to summarize, once again,  the efficiency as a measure of heat rejection
issue is, primarily,  NOT a function of where the pilot actually sets the
red knob.  Rather, it is a function of  the efficiency of the engine at the
BSFC(min) operating condition - - regardless of where the pilot actually
sets the red knob in his normal flight operations.

These comments cover all of the following paragraphs you wrote, and quoted
again below between the rows of asterisks.

I insert some more comments to the remainder of your message further below.

**************************************

>>The TIO-540U2A (note the dash number please) is used in the Aerostar 700
and
has a cruise fuel flow of over 25 GPH/side at FL250 and 75% power, running
~100F ROP for a BSFC of .59.  If you try to lean any farther at FL250, they
overheat.  The TIO-540A2 in the Mirage is about the same;  we have one in
the
shop right now for a new engine.  The TIO-540S1AD updraft engine runs 50F
ROP
at 75% at a fuel flow of 19 to 22 depending highly on the age of the engine.

The updraft engine runs a lower cooling load because it is not exchanging as

much exhaust heat from the pipes to the intake manifold since they are on
opposite sides of the cylinders, as is the arrangement of the downdraft
cooled TSIO-550N.  The factory recommended engine for the Lancair IV
(TSIO-550N) runs at 18.5 to 20 GPH at factory recommended ROP settings for a

BSFC of between .42 and .46.  BSFC min is irrelevant, since all these
numbers
represent max cruise where most people tend to fly their airplanes.  <<

>>BSFC min is measured at the engine's most efficient point, which is
typically
40 to 55% power and LOP for the above engines.  Cruise altitude,
turbochargers and specific configurations change the fuel burn numbers quite

a bit within an engine family.  We cannot take the BSFC min of one dash
number and expect that every other dash number in the family has that same
BSFC at all altitudes, power and mixture settings.<<

**************************************


You go on to say:

>>Yes, people do in fact run these bathtub-chambered,
constant-flow-injection,
wet-fuel-unburned-out-the-pipe engines LOP at max cruise MAP for fuel burns
in the case of the Lycoming of 20 to 22 GPH and as low as 17 GPH for the
Continental.  Yes, there are effects of LOP that are relevant to the issue
of
BSFC and cooling load.

>>First, power is not a constant at a given MAP and RPM.  Higher engine
temperatures, specifically inlet temperature (at the cylinder port) has a
large negative effect on volumetric efficiency, and therefore, power.  Power

also falls off by several percent when the engine is leaned beyond peak EGT.

So calculating BSFC based on a fuel flow running LOP and a MAP/RPM
combination that the factory lists as a given power ROP is cheating.<<


>>LOP does reduce the amount of fuel that burns late in the power stroke,
during the exhaust stroke, and in the exhaust pipe.  This reduces EGT and
with it all of the heat in that radiates and conducts to the rest of the
engine.  However, since power is also reduced, the net gain of reduced
cooling requirements is less than we would hope for.  Dyno testing here is
not as applicable as we would hope, since the cooling and heat transfer
dynamics change dramatically when we get into the rarefied atmosphere of
pressurized cruise altitudes.

Stick the dyno in an altitude chamber and things start to get
interesting...<<

Yes. and I have done that.  And guess what? It doesn't get interesting. The
fundamental laws of physics are everywhere the same.  The
altitude/efficiency/heat rejection issue that you are arguing remain exactly
the same at 17,000' as they do at sea level.

Further, the HARD DATA - - the OEM's HARD DATA - - as well as the data that
I collect almost every day - - is very consistent and conclusive.  Your loss
of horsepower at LOP mixture settings argument is not correct.   HOLDING THE
HP AND RPM CONSTANT  - - the engine making 250 Hp 25 TO 100F ROP will
operate with CHTs about 30 to 40F hotter than the same engine making 250Hp
operating 40 to 70F LOP.  Again, that is not my data, but TCM's data.  It
happens to be correct and true of all  S-I engines - - for reasons that have
almost nothing to do with the arguments about the relative heat rejection of
diesels and S-I engines which started this discussion.


>>Of course LOP may lead to a visit from Captain Detano, so weigh the cost
of
your top end carefully against your fuel bill before you lean too far!  <<

Why do you think that an engine operating 70F LOP is more likely to have a
visit from Capt. Detano than an engine operating 25F ROP at the same HP?
If you think that is true, please provide some data.  

At 25F ROP, the peak cylinder pressures will be hotter and the CHTs will be
30-40F hotter than at the same HP and 70F LOP.  I have never heard anybody
argue that lower CHTs and lower peak cylinder pressures cause increased
detonation risks.

I can run this test on the test stand any time.  Your understanding of this
issue is simply inconsistent with everyday measurements.  It is specifically
inconsistent with, for example,  the published data from the C-W company
concerning the most widely used LOP engine in the history of the world,  the
CW 3350. You can order on original re-print from John Deakin.

..Obviously, an injector set (like GAMI) that gets all of the cylinders to
peak
at the same point is preferable to a set which allows one cylinder to go LOP

while others are ROP.  Better still would be a better engine that doesn't
have unbalanced cylinders to begin with!<<

The problem is not the cylinders.  Rather, the induction system.


>>Most engines run best if they are run quite lean at combinations of high
RPM
and low MAP;<<

Would you like to define "best"?  If you mean "efficient" then that is not
an accurate proposition.

>>  around stoichiometric where RPM and MAP lead to slightly higher
cylinder pressures;  <<

Actually,  stoichiometric will produce LOWER peak cylinder pressures than
will 25, 50, 75, 100, 125, or 150F ROP.  As a matter of fact.

>>... and rich at high MAP vs. RPM which lead to the highest
pressures and temperatures.  Takeoff and maximum continuos power settings of

most aircraft engines fall in the latter category.  Timing should be pushed
to the point of detonation and retarded as little as reliability allows.<<

Ah... no.  That is not really a good criteria and is not the one that is
traditionally used by aircraft OEMs.  

Timing should NOT be " ... pushed to the point of detonation (as reliability
allows)"  under the takeoff condition.  Rather,  timing should be pushed to
the point where the max cylinder pressures are happening at about 15 degrees
after TDC, *OR* to the point where peak cylinder pressures do not exceed
about 1050 PSI whichever happens first.  Once this is done, the engine
should be checked to make sure that routine errors in fuel flow do not
induce detonation.  This would include the standard FAA requirement to check
the engine at WOT with the mixture leaned about 12% from the full rich
specification.


>>As far as heat rejection of diesels and the higher efficiency, I have to
ask
what myth allows such high efficiency to exist at compression ratios of up
to
20:1, yet in the same breath talks about 6:1 open chamber gas engines being
nearly as efficient?<<

It is the "myth" of the hard - - published (for more than 30 years) - - and
verified data.  

>>Caveat Emptor on those fuel burn vs. power ratings.  Unless we mate a real

time torque sensor to the engine in flight at altitude, power cannot be
measured accurately.<<

Well... yes, it can be measured accurately.  But it is no big deal to obtain
in-flight torque data.  Having done so, as recently as  Monday of this week
using a 350 Hp Lycoming engine - -  it correlates rather well with the
previous engine test stand test data for the same engine.

Regards,  George