Power setting table and best economy/best power...

"xerj" wrote in message
...
For example, for the same MP/RPM settings on my Lycoming IO-360, bhp will
be less at best economy vs best power.

That's what my original understanding was, and why I was confused by the
presentation of the power setting table I linked to.

You can prove it simply by leaving the prop and throttle where they are,
and moving the mixture in between best econ and best power. At best econ,
you will be slower than best power. Slower = less power being produced.

However, as Jose pointed out, RPM and/or MP will not remain constant as you
adjust the mixture. Just because the controls have not moved, that does not
mean that the power setting hasn't changed.

If you actually could just get the same power at a lesser fuel flow
without adjusting MP and RPM, putting aside CHT considerations for the
moment, there'd never be a reason to run at best power. It'd just be
burning more fuel for the same result.

Well, that's a matter of current debate, as it happens. The primary
argument in favor of a product like the GAMI fuel injectors is that you CAN
get the same power at a significantly lower fuel flow. In that argument,
you ARE just "burning more fuel for the same result" by using the "best
power, rich of peak" mixture settings suggested by engine operating manuals.

I find the argument compelling. The proponents explain that the
rich-of-peak, "best power" mixture settings exist to provide enough excess
fuel to ensure that no cylinder is actually running at peak EGT (since in
most engines, the actual mixture from one cylinder to another varies by a
significant amount), and to provide cooling for all cylinders to compensate
for the high power setting used.

They go on to explain that if the fuel mixture is actually well-matched from
one cylinder to another, one can accomplish the same effect by running the
engine lean-of-peak, ensuring that all of the fuel in the air/fuel mixture
is burned (rather than some of it being used to cool the engine), but still
keeping the EGT low enough in each cylinder to avoid heat-related problems.

Whether all of that is correct, I do not know. I'm not the expert. But it
does makes sense to me, and yet is still consistent with operating the
engine rich-of-peak for engines that aren't designed to ensure evenly
matched fuel/air mixtures for each cylinder.

Pete