CHT on #5 3300
Posted: Mon Mar 28, 2016 9:20 pm
by kmwoody
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
Re: CHT on #5 3300
Posted: Mon Mar 28, 2016 9:42 pm
by fastj22
Open the cowl exit a bit. You’ll be amazed at how much cooler it makes everything.
Re: CHT on #5 3300
Posted: Tue Mar 29, 2016 6:48 am
by kmwoody
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
Re: CHT on #5 3300
Posted: Tue Mar 29, 2016 6:14 pm
by N111YX
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… 
Re: CHT on #5 3300
Posted: Tue Mar 29, 2016 6:41 pm
by fastj22
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.
Re: CHT on #5 3300
Posted: Tue Mar 29, 2016 7:20 pm
by DCASonex
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
Re: CHT on #5 3300
Posted: Tue Mar 29, 2016 8:47 pm
by kmwoody
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
Re: CHT on #5 3300
Posted: Wed Mar 30, 2016 7:24 am
by DCASonex
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.
Re: CHT on #5 3300
Posted: Wed Mar 30, 2016 10:17 am
by N111YX
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…
Re: CHT on #5 3300
Posted: Wed Mar 30, 2016 3:03 pm
by kmwoody
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
Re: CHT on #5 3300
Posted: Wed Mar 30, 2016 8:59 pm
by Sonex-1081
Just adding my results here…I have the Jab 3300 with an Aeroinjector and ‘under the plug ring type’ CHT sensors to an MGL iEFIS. I have clocked up 16 hours. OAT is generally 25-32deg C (damn HOT). My installation is almost exactly as per the Sonex baffle kit instruction book and I consistently have #1 as the hottest cylinder running at about 160 degC with #3 #5 both at 150degC. #'s 2,4 & 6 all run much cooler at 125-133 degC with #4 being the coolest. I tried trimming the front baffle plate on the Right Hand Side and drilling a couple of holes in it to get more direct cool air on #1 but no real result from that. I also have the nose gear version (with offset leg on Left side) and I run mine without the cover plate that wraps around where the gear leg exists the cowl…This means the LHS cowling outlet area is a fair bit larger than the RHS. I’m not sure whether this is the cause of the LH/RH side temp spread. I think I will try installing the cover plate to reduce outlet size on LHS and see what happens. Any ideas for a more even spread would be great.
Re: CHT on #5 3300
Posted: Thu Mar 31, 2016 8:20 am
by DCASonex
Sonex 1081: Your CHTs are sufficiently different from most that I would double check that your sensors are reading the cylinders you think they are.
David A. CAMit 3300 in Sonex TD
Re: CHT on #5 3300
Posted: Thu Mar 31, 2016 7:56 pm
by LarryEWaiex121
Sonex 1081,
Along the lines of what David just mentioned, I’d make darn sure your seeing what your seeing. By that I mean pull the plugs and run around the engine one plug a time with a propane torch and lightly wick each one and have someone sit in the plane and call out the cylinder# and confirm your numbering order on the sensor’s. If your 100% convinced they are correct then you have to start from there.
On my Jabiru 3300, # 2 was always the warmest over a variety of flight conditions, #1 was mostly the coolest, #5 and 6 in the rear were consistently the most stable. Number 3 and 4 in the middle normally split the difference between the front and rear holes.
I completely resisted the theory that the under plug thermocouples could be at fault but I found out different. I experimented with tighting the plug and working diligently with getting the sensor centered and it changed my readings on the high reading holes by as much as 30 degrees F and convinced me there can be significant error just in the instrumentation based on your install.
Quite honestly, getting back to your particular setup, you don’t have enough time yet to have a broken in engine. Obviously you don’t want to bake your engine but, your readings will all come down after about 30-50 hrs. It takes that long for things to settle in.
Till then I would make certain mixture is adequate(plug color), temps are in bounds and oil is at no more than mid level. Anything more then mid stick on the oil will make the whole engine hotter. Good luck.
Larry
Waiex121YX