MoGas Long Term Test: 5000 gallons and counting...

Jay Honeck wrote:

Huh??? On my 230 hp O-470, I cruise at 23-squared, without any fancy
engine monitors. Using the "pull-until-it-feels-about-right" method of
leaning, I get 12 gph.


I can lean to that fuel flow without any undue engine sounds, too. But my
EGTs go well over 1500 degrees, and my CHTs push 350 when I do.

EGT is irrelavant and 350 is not hot.

In rec.aviation.owning Newps wrote:
: I can lean to that fuel flow without any undue engine sounds, too. But my
: EGTs go well over 1500 degrees, and my CHTs push 350 when I do.

: EGT is irrelavant and 350 is not hot.

Exactly. The absolute value of EGT does not matter... almost all of the
cooling of the exhaust valves is done through the valve seat (and stem in Lycoming).
Thus, the "cold sink" is the cylinder, and CHT is what's important. Lycoming redlines
CHT at 500, recommends 450 as a max, and general wisedom dictates anything under
375-400 in cruise is fine.

Also remember that EGT and CHT probes are often uncompensated thermocouples.
That means they read the difference between the "hot" thing, and the temperature of
the "cold" (where the J thermocouple wires connect to the copper wires going to the
meter, etc). They're generally set to be accurate at about 70 degrees F. If it's 0
F, the temp will read 70 degrees hotter than it actually is. Wintertime temps read
higher for that reason.

I don't know about the fancy JPI, etc, by my dumb gauges definately do this.

-Cory



--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

On Tue, 10 May 2005 20:43:34 +0000 (UTC),
wrote:

Exactly. The absolute value of EGT does not matter... almost all of the
cooling of the exhaust valves is done through the valve seat (and stem in Lycoming).
Thus, the "cold sink" is the cylinder, and CHT is what's important. Lycoming redlines
CHT at 500, recommends 450 as a max, and general wisedom dictates anything under
375-400 in cruise is fine.

Deakin posts a chart from Pratt and Whitney in his "Mixture Magic"
column which verifies this precisely. In the chart is a line
depicting the loss of strength of the aluminum alloy used for cylinder
heads. It starts dipping LONG before 400 degrees is reached and is
plummeting at 450 degrees.

See: http://www.avweb.com/news/columns/182084-1.html

He recommends running at 400 degrees or under for cruise.

Corky Scott

: Deakin posts a chart from Pratt and Whitney in his "Mixture Magic"
: column which verifies this precisely. In the chart is a line
: depicting the loss of strength of the aluminum alloy used for cylinder
: heads. It starts dipping LONG before 400 degrees is reached and is
: plummeting at 450 degrees.

: See: http://www.avweb.com/news/columns/182084-1.html

: He recommends running at 400 degrees or under for cruise.

I knew I'd read it somewhere and suspected it was a Deakin article.

-Cory

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

: He recommends running at 400 degrees or under for cruise.

I knew I'd read it somewhere and suspected it was a Deakin article.

Actually, Lycoming says this, too. (It's on their website.)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"