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   At the time I bought the IO-550-G2B engine for my first ES, Continental
were actually advertising it as the "lean burn" engine, touting the benefits
of their re-designed intake manifold in balancing air/fuel mix for running
LOP without roughness, blah-didi-blah . . .  Sure enough, that engine did
run very smoothly lean of peak, and for almost all of the 80 hours I flew
it, that's how I ran it.  The fuel burn rich of peak was about 15 to 15.5
gph with an IAS of about 192kts (around 8000' or so), whereas flipping over
to LOP operation, fuel burn ran about 12 gph with an IAS of about 183 kts.
CHT's were actually cooler running the EGT at 60 to 75 degrees LOP, and in
my book giving up 5% of cruise speed for a 20% reduction in fuel burrn is a
pretty good bargain.  When the plugs were pulled for a pre-sale inspection,
they looked just like they're supposed to look: a slightly tan gray color,
with no evidence of burning or fouling.

   The odd thing about it is that when I tried to discuss this with one of
the TCM reps at SnF last year, he actually got pretty huffy at the whole
idea, was adamant that TCM did not, had not, will not, EVER recommend lean
of peak operation, etc., etc.  Denied they had ever advertised any such
thing as a "lean burn" engine -- well, you get the idea.  So, wha happened?
Maybe some of the IV-P guys burning cylinders backfired all down through the
marketing and engineering depts?  Can't speak for the turbo'd versions, but
the non-turbo IO-550 is happy as a clam running LOP.  I should be firing up
my new IO-550-N (same engine, exactly, but a new letter and a different
stated HP.  ??) in a week or so, and when it gets flying, it'll be doing it
lean of peak most of the time.

   Gotta admit, though, there were times I wasn't quite sure what to do
with that mix knob.  Say, you're at FL140, start down, hit bumps around 6K,
and slow to something around spam can speed.  Flip over to rich now?  Or do
you just chase the peak down, easing the mix in to keep the same LOP margin?
It's one of the times that FADEC would be nice to handle such chores, but of
course, TCM's FADEC will never, ever, set things up for lean of . . . .
sigh.

Jim Cameron
N143ES

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