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Date: Tue, 07 Jul 2009 08:02:05 -0400
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From: "Robert Pastusek" <rpastusek@htii.com>
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Subject: RE: [LML] Engine settings - TSIO-550
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John Barrett wrote:

The TCM guidelines are clear and that is probably fine to go with (?) but is
there any reason to modify this with a Performance Engines engine with one
Lightspeed ignition and one mag?

John,
I originally set up my Performance Engines TSIO-550 (2 mags) to flow 43 GPH
at 2700 RPM and 38.5" MP on takeoff. My technique is to advance the throttle
all the way over about 3-5 seconds to minimize rudder/braking and prop
damage at the start of the roll, and I get to those numbers at about 10
seconds after reaching full throttle on TO.

I climb at full rich, 2500 RPM, approx 32" MP and 160 kts after the airplane
is cleaned up. This requires periodic throttle adjustment to maintain 32" MP
as I climb, and results in a fuel flow of about 30 GPH and very cool running
engine. Over the winter, I noticed that the fuel flow was slowly decreasing
during both TO and climb...to about 38 GPH and 27 GPH respectively. Also, as
the weather got warmer this spring, I saw cylinder temps (#3) reach 380
degrees for the first time ever (at about 200 hours TT engine & airframe). 

During the condition inspection in May (250 hrs TT), I boosted the fuel flow
back to 43 GPH on TO with the above MP and RPM settings. This returned my
cylinder temps to below 380 until today, when I hit 380 passing 15,000' in
the climb on #3. This was over New Mexico, with surface temps above 100 and
the ISA deviation at 15,000 at +40 degrees. I leveled at cruise altitude of
16,000 and the cylinder temp quickly dropped back to its normal 340 or so.
This was an unusually hot day and the cylinders never got near the 420
recommended as max continuous, so I'm thinking the fuel flow and technique
are still OK.

The new Continental specs call for a fuel flow of 38 GPH at the above (TO)
settings. The old spec was 44 GPH. I don't know why they changed...perhaps
because the engine will quit if fed too much fuel and they wanted to
introduce a safety margin? My engine quits at about 48 GPH on TO roll on an
approximately standard day (ask me how I know). 38 GPH is not enough fuel
flow to keep my cylinders cool during less than full-power climb (32" MP @
2500 RPM). It might be OK at full throttle/2700, but I have never run the
engine that hard for the extended time it takes to climb to altitude, and
don't intend to. So for me, 43-44 GPH seems to be a good TO fuel flow
setting for my engine.

BTW, as noted in a recent post, turning the boost pump on high on TO will
run the fuel flow to about 48-50 GPH and stall the engine... It will also
stall the engine if turned on high at idle. Some run the fuel pump on low
continuously from engine start. I set my engine up to the above figures with
the boost pump off. My rationale is that the engine runs fine without it; if
the engine pump fails, the boost pump will keep it going, at least at
partial power. If the engine is set up to run optimally with both
engine-driven and electric boost pumps on, a failure of either pump will
cause a problem. At the minimum, the engine won't develop full power, will
over heat, and may stall.

This is all from reading several sources that disagree slightly, and my own
testing/experience. I'd welcome the views of others, and any better
sources/rationale!

Bob