Cessna 340 High Altitude Operations (Please Help)

On 1/30/11 4:58 PM, UIO Spotter wrote:
/snip/
NOW, on the 340, I was reading the manuals and the takeoff procedures
say MIXTURE RICH. Now. I have some doubt. As we are taking off from 9
thousand feet I find it hard to believe the mixture needs to be rich!
And based on my experience thats not right. The books don't say
anything regarding high altitude takeoffs so Im lost. Is it correct to
take this plane off with the mixtures rich regardless of the altitude?
In the MAXIMUM CLIMB checklist you see the following

1. Power 2700 Full Throttle Below 20,000FT
2. Airspeed 108
3. *Mixtures FULL RICH BELOW 20,000FT
LEAN AS REQUIRED ABOVE 20,000FT*
.......

This is the only LIST or thing I could see regarding Maximum Climbs etc,
but I will keep on looking. So, whats your take on this guys? I
believe id be killing my performance with the engines at that rate of
fuel flow. But thats why I am asking. We used to take it off like
that, we had a long takeoff roll, but it had a good rational climb. But
tell me what you think
/snip/

Stefano,

The big difference here is that the 340's engines are turbocharged, and
have altitude compensated fuel injection pumps. The engine in the 172XP
you flew did *not* have either of those features. To make a long story
short, Cessna's published leaning procedures are correct, i.e full rich
below 20,000 ft., for full power takeoffs and climb. This is because the
turbochargers will provide the engines with Sea Level manifold pressures
up in to the 12-15,000 ft. range, and the injection pumps will
automatically lean for best full rich performance above those altitudes.

Happy Flying!
Scott Skylane