John,
I “hope” my smiley face communicated I was trying to be funny.
Yes, I “suspect” that if you left the fuel settings LOP the TIT temps would have been good. Your CHT’s never went up, so they were not a problem.
Here are some numbers I know and logic to get to your power settings.
a.
2500 RPM and 32 inHg…..I want 17.6 to 18.7 gph FF (the fuel setting depends on OAT and altitude. In the FL’s, the turbo is working harder and inlet
temps go up thus fuel flow is reduced)
b.
2400 RPM reduces power ~4%
c.
28 inHg reduces power ~6.5%
So you would want to pull the mixture back to ~15.8 to 16.8 gph at 2400 RPM and 28 inHg. Your engine may be slightly different but I think this is a great place
to start.
I go from full rich to LOP in about 5 seconds and the TIT’s don’t have much of a chance to go up past 1640 degF. CHT’s move slowly and are never a problem during
this transition.
If you expect to see TIT’s in the low 1500 degF or below range like you do ROP, that will never happen LOP but your CHT’s will be happy never the less.
I suspect your peak TIT is around ~1725 degF (this depends on compression ratio), so 75 deg LOP is ~1650 degF. While I personally would not cruise at 1680
degF TIT, that temp is not cause for panic. The turbo is good for 1725 degF continuous. I normally find my CHT’s are below 380 degF (my personal max) if my higher TIT is around 1640 degF or a little less. The two TIT’s temps vary some due to the amount of
pressure going thru the wastegate….at least that is my theory. I have had to lean further at FL250 and ISA +35 to keep CHT’s below 380 degF.
Here is my “suggestion” on learning to run your engine LOP.
-
Climb full rich. Level off at cruise altitude.
-
Set manifold pressure to 28 inHG
-
Reduce RPM to 2400
-
Pull mixture to 16 gph and check TIT. (get to 16 gph with a nice steady pull…5 seconds or so…don’t lollygag around 18-19 gph)
-
Tweak mixture for 1640 TIT and then cruise and watch CHT’s. This time of year I would expect 340 degF at 17,000 ft in my plane. (Phoenix area)
Craig Berland
N7VG
Fair question, Craig despite the use of the perjorative term "wussy". I'm interested in running my engine fairly conservatively especially while I'm learning how to protect it from events that are detrimental to it. I may decide to continue
running in that percentage of power range or may start pushing it up a bit as I get more comfortable.
The third attempt to lean went quite a bit beyond what the engine could handle evidenced by enough engine roughness that I thought it might quit.
I did not leave the settings for more than a second due to the immediate alarms and temps I was seeing. Are you saying that if I had left the FF lean for some time those temps would start back down?
John,
Why were you running such a wussy power setting?
J
Looks like your TIT’s were high because you never leaned far enough for that power setting.
Craig Berland
N7VG
We returned home yesterday from East Coast visits following LOBO mtg in Greenville, SC.
On the way to Greenville after an intermediate stop in NE, we experienced an engine problem that I brought to the attention of anyone
at LOBO who would listen and give advice including Neil George from TCM with Allen Barrett hooked into the discussion by text and cell phone.
The short story is that when I reached my planned VFR altitude of 15,500 and levelled off I pulled back power but forgot to lean or reset prop for about ten minutes. Then when I remembered and tried to lean
the engine, TITs skyrocketed followed by hot EGT readings. See the attached link to the
Savvyanalysis graphing of the engine behavior and see if you can come up with what went wrong. When you review the graph, you’ll likely notice that I tried twice more after the initial leaning
to see if I could get lean of peak and the engine emphatically let me know it did NOT like what I was doing.
I can tell you the problem
has been resolved and we flew the airplane around the country for another week with no repeats. Now I'm interested to know what LMLers might think caused this because I was totally surprised
when I learned what the real problem was.
Some of you who were supportive at LOBO already know the answer so let’s see what others come up with. I have many people to thank for amazing help in finding
and correcting the problem so I want to go on record as one of the most appreciative people there could be for LOBO, our many vendors and for pilots around the airport in Greenville who gave advice, time, materials, loaned tools and so on.