Posted for George Braly <gwbraly@gami.com>:


Doug,

Try setting up your engine, just as you describe below.

THEN, nudge the MP from 27.8" up to about 30-31" - - you should stay lean of
peak and have all of your original HP back.

With that engine,  when you are, in fact, LOP,  then you can calculate the
HP rather accurately, by the following:

Hp = FF(gph) X  14.2 And, yes, before you point out that I have used 14.9 for other engines and
13.9 for still other engines, it is also true that the TSIO-520BE and
TSIO550B engines are a bit peculiar.  While they share the 7.5:1 compression
ratio of the engines that normally end up with a 13.9 number, they are
"different" in that the timing is often set to 24d BTDC which improves the
efficiency in cruise, a bit.

However,  that 24d BTDC timing comes with  a serious price.  That serious
price is that the engine suffers very high peak cylinder pressures during
full power operation - -   UNLESS  --- BIG UNLESS - -  you make darned
(darnded as in DAMMIT get it right!) sure that the fuel flow on take off is
really really rich as it really should be.

Regards,  George

PS.  There is no magic for this.   Look up the book BSFC(min) for your
engine in the TCM manual.  Across a broad range of LOP mixture settings it
will be around 0.41 lbs/Hp/hr.   If fuel is 5.82 gal/hr then      5.82/0.41
= 14.195 or  14.2Hp/GPH.  In the case of my IO-550 with 8.5: compression and 22d spark advance,  the
BSFC(min) is around 0.385.   I use 0.39 as an average across a broad range
of LOP mixture settings, and thus,   5.82/0.39 = 14.9 Hp/GPH.