SonexBuilders.net

Hi all,

I have finished installing my CAMit in Sonex 959. I have flown it several times and it is a powerhouse compared to the Aerovee. It almost pulled me off the runway on the first flight. I was quite prepared to use right rudder instead of left but I underestimated the torque of the 3300 engines.

I am having issues getting cylinder #5 under 300F in cruise. The left bank has always been under 300F. On the right bank #3 was my hottest until I added an additional 3/16" on top of the 3/4 " I started with and the temp on came down 60F. Go figure? Maybe it came down so much because the 3/4" was a taper and the 3/16" was 90 degrees to the airflow.

I have been able to get #5 down to 320F but no matter what combination of deflectors I try, I cannot get the temp lower.

If anyone has a tip or trick that worked for them, please let me know.

I have figured out through my many decowlings that with the leg farings off my CHTs go up 15F and the insulated CHT covers from CAMit add 20F to the readings.

Ken W
Sonex 959
CAMit 3300

Open the cowl exit a bit. You'll be amazed at how much cooler it makes everything.

I tested my cowl outlet by blocking off all but 2 square inches of the oil cooler opening and the CHTs stayed the same. I would think that indicates the exit area is large enough. Am I missing something?

Ken W
Sonex 959

I gave up trying to balance cylinders after noting significant changes every time I re-installed the cowling. One question you may ask is are you reading the temperature of the cylinder, or the temperature of the sensor? I have the "around-the-plug" type so I'm probably off to a bad start anyway.

I just turned over 606 hours of engine time and all cylinders make good compression and the oil analysis is clean. My trick is to use slow throttle changes, monitor all six EGT's and keep all cylinders happy by watching the temps, and not worrying much about CHT balance. It's worked so far.

Now if I could just pin down the high-running #6 EGT the world would be perfect... :)

Kip,
I've tamed the hot #6 (EGT) a bit using an air straightener and Rotec throttle body. 5 and 6 EGT still are the hottest in climb but not spiking like they did with the Aerocarb. In cruise, they balance out nicely.

My nickel theory and worth every penny....
The hot 5/6 is probably due to insufficient atomization of the fuel to the closest cylinders. The further away boys get better atomization. I think the Rotec does a better job at atomization due to the fine spray bar vs, the tapered needle of the aerocarb. And the pre-carb air straightener helps keep turbulence down.

One thing I have done that seems to help. Look down on the cylinder head fins and you will see that there is more fin extending on one side of each head than the other. On # 5 cylinder the solid area around the head bolt on the aft most side almost contacts the back side of the intake plenum, while on #6 the fins extend enough to leave space for airflow. I cut a couple of small rectangular holes in the back side of the intake plenum behind #5 just above that bolt so as to get airflow through the fins. Total area of the two holes only about 1 square inch, but that knocked off a few degrees and my CHTs are all quite close. No drawing or photo at this time.

David A. CAMit 3300 # 0004 in Sonex TD #1327

N111YX wrote:I gave up trying to balance cylinders after noting significant changes every time I re-installed the cowling. One question you may ask is are you reading the temperature of the cylinder, or the temperature of the sensor? I have the "around-the-plug" type so I'm probably off to a bad start anyway.

Kip, what is your range of CHT temps? Mine are 250 #6 to 320 #5 measured with the sensor between the spark plugs and covered with an insulator. I switched 3 and 5 to test the accuracy, they were reading properly.

DCASonex wrote:On # 5 cylinder the solid area around the head bolt on the aft most side almost contacts the back side of the intake plenum

David, not sure if I understand what you are explaining. On #5 the cylinder sticks out farther than the head, so I have a 3/16" gap between the head and the plenum. At one point I attempted to block that gap because I figured the air was bypassing #5 altogether and flowing to the back of the plenum and out.

I am wondering about the cowl intake openings. I figured I would have to modify the openings after I removed a counterclockwise rotating engine and installed a clockwise rotating engine. From what I see, they are set up the same for the Aerovee or the Jabiru.

Ken W

Ken,

The fins of the CAMit cylinders do push the back wall of the Sonex plenum out a bit allowing an air gap for flow through the head fins. It may be that mine is mashed around enough to be a bit tighter to the head than yours such that adding the holes made an improvement. Or might be that adding the holes aids cooling by just getting more air flowing through there ?

The comment about the varying CHT readings may be yet another confirmation of the value of removing at least one variable from the system by insulating the leads of the thermocouples to keep those from draining off heat in a manner that will vary with airflow around the wires rather than through the fins of the heads. Your noting that those read about 20 degrees F higher with the insulation is in line with my findings but is a variable. The relatively long exposed neck on the under-the-plug ring terminals also adds a variable in that the actual point of the thermocouple is father from the heat source intended to be measured and thus somewhere along the gradient between source and much cooler wires out in the air stream, that insulated thermocouples on the center hole minimizes.

David A.

kmwoody wrote:

N111YX wrote:I gave up trying to balance cylinders after noting significant changes every time I re-installed the cowling. One question you may ask is are you reading the temperature of the cylinder, or the temperature of the sensor? I have the "around-the-plug" type so I'm probably off to a bad start anyway.

Kip, what is your range of CHT temps? Mine are 250 #6 to 320 #5 measured with the sensor between the spark plugs and covered with an insulator. I switched 3 and 5 to test the accuracy, they were reading properly.

DCASonex wrote:On # 5 cylinder the solid area around the head bolt on the aft most side almost contacts the back side of the intake plenum

Ken W

Ken, I run from 220 (#1) to about 310 (#5). That #1 always runs cold. I think the ram air blows right on the sensor. #2 runs about 60 degrees warmer. Like I said, I don't worry about it. If the hottest cylinder is below the maximum and the coolest is above the minimum, I'm content....

N111YX wrote:Ken, I run from 220 (#1) to about 310 (#5). That #1 always runs cold. I think the ram air blows right on the sensor. #2 runs about 60 degrees warmer. Like I said, I don't worry about it. If the hottest cylinder is below the maximum and the coolest is above the minimum, I'm content....

Well that makes me feel better about my temps. Without the insulated covers that add 20F my temps would be 230 to 300. I have not attempted any balancing of the temps. I have concentrated on getting the hottest cylinders under 300. I will work on balancing, but good to know my attempts might be futile. I'm sure my temps will come down slightly as the engine gets fully broke in.

Thanks everyone for your help.

Ken W