The CMI turbo has unfortunate safety feature that the fuel flow does not linear respond to the power lever position.
The last bit of MP change on the way up and way back between 30” and 36.5”
If the power lever is at full travel the amount of fuel increases greatly compared to the air.
If one pulls the power lever back slightly. The engine has a leaner ratio.
With that muddied up.
I strongly encourage the use of the TIT indication for proper expected air to fuel ratios.
A conforming T is 1320f -1340f while full rich at full MP. A higher TIT is a leaner ratio, single mag operation, poor timing or too rich condition which is not being consumed in the combustion chamber.(and sound like a gutter moan of a mastodon charging ).
Thank you for your reply so when I am at cruise after leaning 30.5MP or less and then reducing FF to around 16.1 to give 75% power my TIT are averaging still 1600 but usually closer to 1650. Is that normal?
He’s going to say post your data. You have to know if your mag timing is off. You have to know if your MP is calibrated. Mine is not, rather than recalibrated, I just run at 31” MP, then I lean to 1580 TIT. Today was really cold and I had FF of 16.8-17. In the summer it might be 15.7-16.
Also, when you lean, the MP tends to go down, so you have to bump it back up.
I just the data card (top MFD card slot) and put into a computer that has an SD card reader. Go to the datalog file and all your flights are there in .cvs format. That’s what we want.
The most important part is the ground full rich mag check. You should check each mag and both position for 1 minute each.
I run at 31” MP because my MP is not quite calibrated exactly. That’s not too important. The important part is to lean to 1580 no matter what your MP is.
I am surprised jo one has invited you to the main Forum. Its a great place of exceptional people and discussion. It coats a about the value of 20 gallons of 100LL.
You can select and search for lots of subjects from experts, smartypants and experienced people who learned lessons the hard way.
Its not facebook, beechtalk or “X”.
And you can upload your engine data there….
And someone will probably look at it…
And show whats not optimal and how you could make some easy changes to the engine and how you fly.
^^^this 100%. Proper procedure for the ground mag check is:
Mixture full rich
1500 RPM
Minimum 30 seconds on each mag with 30 seconds on both to let things normalize.
this will give the data that’s needed to check for timing.
The next level of timing is to do a high-altitude LOP mag check. Go up to 12,500 on a good VFR day, go LOP and then do a mag check. There’s more of a detailed procedure for that, which, as Jim mentioned above, by joining COPA you’ll be able to search for and then do that procedure by the book so that experts like Jim and others can look at the data and give you next best steps to tweak the big fan hanging off the front of the airplane.
Thanks Jim. Is the fuel/air mixture change the reverse when pulling MAP from 30.5” to lower numbers (e.g., 25”) for a descent from cruise? When I pull MAP for a descent from LOP cruise, I need to simultaneously reduce mixture to avoid a rise in TITs. I assumed this was because my fuel/air ratio would become more rich, with the MAP pull only, in this situation. (That wasn’t the case in my former plane, a 22TN.)
Take your mixture to below the blue line (as long as the engine does not run rough). if you can get it to 16 or 15.9 it will help the TIT go under 1580.
Thank you. I will try that. Annual is coming up in a month so will have mechanic look at the MP warning too.
What I was taught was once at cruise I lean. But when I clean or descend to a different altitude start the process over again. Unless a continued descent to land I keep it at its setting until under 3000AGL and then I put full mixture in.
