: The other indirect reading of fuel flow will be the EGT. How much lower than
: high-power cruise peak is it on full-rich takeoff?

: Less than the 200?? you mention. Peak EGTs while leaning are perhaps
: 200?? above climb-out EGTs, but I have been advised to run 125?? rich
: of peak by my mechanic. At 50?? lean of peak the exhaust pipe has a
: light grey appearance that suggests a too-lean mixture.

One universal truth in aviation seems to be that there are more untruths than
can be counted. Lots of old-wives-tales, especially regarding leaning. Reading
Deakin's articles on AvWeb should be required reading. Bottom line is that the engine
cannot be harmed with the mixture knob at 65% (or 70%) power so long as CHT doesn't
get too hot. Light grey exhaust pipe to me indicates a correct mixture where there's
not an abundance of either fuel or air, and the lead is being scavanged nicely. 125
rich is burning a lot of extra fuel, depositing lots of carbon on the pistons, valves,
and valve guides.

: Probably not getting more than 5-10hp out of it. Of course, all that assumes
: the tuned exhaust actually works... ;-)

: Well, all I can say is that I noticed the difference after installing
: it. But to be fair, it wasn't a very scientific experiment because I
: also installed an O-360 and a c/s prop at the same time. Those three
: items conspire together to make it a real hot rod, among elderly C-172s
: at least. Too bad the aerodynamics resemble that of a 1978 Volvo 240DL.

That's a whole 'nother kettle of fish. The CS will let you actually *make*
rated HP at sea level. Putting a CS prop on a fixed-gear bird will not get you any
appreciable speed. It might give you a bit better economy if you can run it
over-squared. The only thing it buys you is takeoff/climb performance, and unlikely
to have increased your legal gross weight any.

-Cory

--

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