EGT changes with MP/FF

I'm trying to understand the pattern of EGT changes in my IO360/airflow performance FM200/dual pmags engine when I reduce the throttle while maintaining altitude. Diagram attached, and I've manually added the values at "interesting" times.



When I'm flying along with full throttle all the EGTs are about the same, with only 27 degrees spread. When I reduce throttle and maintain altitude, two EGTs (3&4) start going up quickly, the other two a bit later. Continuing to reduce throttle, they all reverse, start dropping, but 3&4 stay together, and the other two change at different rates, eventually with #2 and #1 at very different EGTs. Adding throttle again gets them all together as before. Performance and smoothness are excellent. Without the engine monitor I would not suspect anything is wrong.

Does this indicate something that I can improve? I recently installed Ross's intakes as I suspected a leak, but that didn't seem to change anything. Injectors are clean. Plugs look very good. Thanks in advance for any hints or ideas.

Need MAP data as well. Also, try leaning with the mixture to see what happens (Lean over 3+ minute period); Leave throttle constant. Also, measure spacing from EGT probe to flange, looking for consistency.

Larry

Send a link to your flight.

You should be doing this with mixture (as Larry said), not throttle. Different EGTs don't matter much; what is important is that they peak at the same time.

Read the method at the following link.

https://resources.savvyaviation.com/resources/other-documents/flight-test-profile/

link

The link to the flight is below.

https://apps.savvyaviation.com/flights/4575992/e8d8460a-874c-4096-b7aa-438103a85d13

I was doing a test required which is run at full speed at a fixed altitude and reduce the speed slowly. This is to check the airspeed calibration. I ran the tests at about 0/120/240 degrees, clean, takeoff flaps, and full flaps.

Looking at the EGTs I saw the behavior that seemed unusual to me. Perhaps it's normal, not sure, but I would have expected all the EGTs to stay roughly together.

MAP graph is almost identical in shape to FF.

Happy to get your feedback and hints!

Perfectly normal.

Look at your fuel flow. At high fuel flow, nozzle diameter sets GAMI spread. At low flow, GAMI spread is a function of the flow divider; the nozzles are too large to affect flow. The transition to divider-dominated spread starts as flow drops below (ballpark) 7 GPH, which is exactly what you're seeing.

If you want to extend your very good GAMI spread to some lower fuel flow, install smaller restrictors in the nozzle bodies and re-tune for spread.

BTW, this is one area in which EFI is superior. Nozzle pressure is constant regardless of flow rate; only the injector open time changes. The GAMI spread remains relatively constant down to very low flows.

DanH said:

Perfectly normal. ...

Click to expand...

Thanks Dan, really appreciate the feedback. Makes perfect sense now. Once I get a few cross-country trips at altitude under my belt, I'll know if 7 GPH is low enough. If needed, I'll check with Don about smaller nozzles.