CKeller
Premium Member
- Joined
- Aug 18, 2006
- Messages
- 268
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- 25
Hello everyone ~
I put an engine monitor (JPI EDM 700) into my Skybolt (O-360A1A fuel injected) earlier in the year and I now understand the expression "Ignorance is Bliss". The monitor revealed high CHTs on climbout (and in cruise) on the rear cylinders (#s 3 and 4)...they will pass 420 degrees before I am out of the downwind if I do not reduce RPM, enrichen the mixture, and shallow my climb. Unacceptable.
The EGTs are normal, so I do not suspect a lean cylinder. I checked the fuel flow nonetheless and looked for leaks...nada. Checked timing, borescoped, plugged holes in the baffling. Nothing helped. Swapped probes...well, you get the picture.
This weekend I fabricated a dam out of sheet aluminum to block airflow hitting the forward cylinders and to deflect the airflow up and over to the rear cylinders. It made a big difference in the temps of the front cylinders, and brought down the rear cylinders' temps a bit...now they are all around 400 degF in the downwind. Hmmm.
The aircraft has a plenum over the top of the engine to create the high pressure area. I am beginning to wonder if the volume within this area is not big enough to pass enough air through the cylinders. The exit area on the lower cowl is big, so I think that is ok. Has anyone had similar issues where they had to do modifications to their front cowl to admit more air or create higher pressure on the top of the engine? I am about to spend some time building silicone baffling to seal against the top cowl, to see if a bigger area wold make a difference. This is going to take a bit of time to fit, so before I begin, I am open to suggestions.
Here's a shot of the front area of the cowl...you can see cylinders 1 and 2 blocking most of the surface area. I do not have a pic of the modification I just tried.
Thanks!
>Colleen
I put an engine monitor (JPI EDM 700) into my Skybolt (O-360A1A fuel injected) earlier in the year and I now understand the expression "Ignorance is Bliss". The monitor revealed high CHTs on climbout (and in cruise) on the rear cylinders (#s 3 and 4)...they will pass 420 degrees before I am out of the downwind if I do not reduce RPM, enrichen the mixture, and shallow my climb. Unacceptable.
The EGTs are normal, so I do not suspect a lean cylinder. I checked the fuel flow nonetheless and looked for leaks...nada. Checked timing, borescoped, plugged holes in the baffling. Nothing helped. Swapped probes...well, you get the picture.
This weekend I fabricated a dam out of sheet aluminum to block airflow hitting the forward cylinders and to deflect the airflow up and over to the rear cylinders. It made a big difference in the temps of the front cylinders, and brought down the rear cylinders' temps a bit...now they are all around 400 degF in the downwind. Hmmm.
The aircraft has a plenum over the top of the engine to create the high pressure area. I am beginning to wonder if the volume within this area is not big enough to pass enough air through the cylinders. The exit area on the lower cowl is big, so I think that is ok. Has anyone had similar issues where they had to do modifications to their front cowl to admit more air or create higher pressure on the top of the engine? I am about to spend some time building silicone baffling to seal against the top cowl, to see if a bigger area wold make a difference. This is going to take a bit of time to fit, so before I begin, I am open to suggestions.
Here's a shot of the front area of the cowl...you can see cylinders 1 and 2 blocking most of the surface area. I do not have a pic of the modification I just tried.
Thanks!
>Colleen
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