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Hi Mark,

The weight can’t rotate because the nut end of the bolts is part way inside the prop flange holes. It could possibly shift slightly, but not enough to matter. I’m of course going to keep a close eye on it.

I flew about 2 hours ago and it was very smooth.

CO/EGT and Hush Pipes

https://youtu.be/hl8BgYhRW9o

Hi Paul, thanks for posting the video, that's an effective way to find leaks! I have the same
baffle setup as you on my 3300. My chts are all between 135C and 155C, except for number 5
(Right rear) which is 155C to 175C. This is while doing touch and goes on a 22 deg C day.
My chts were all higher before I taped off part of the oil cooler air intake on the cowl. It seems
there was too much air getting into the lower cowl, preventing the air over the heads from
exiting the cowl.
I'm curious what your chts are and if mine are in the ballpark.

Thanks!
Rick
C-GRIX

Hi Rick,

My CHTs vary a lot. Basically, the left side of my engine is cool/rich, and the right side is hot ( yet in the green).

I’m should try to rotate the carb counter clockwise to see if I can get more fuel to the right side of the engine.

Last flight during cruise, #1 was 338F and #6 was 188F. Pretty extreme. It’s not usually that bad though.

That does sound like a very large spread. Tilting the cab, assuming a Bing Carb, will affect the EGT's much more than CHTs. How do your EGTs look ? The Jab engines originally had a stream lined flow divider in the intake manifold, later ones had two round rods that produced more turbulence and more even EGTs and also lessened the effect of tipping the carb. Unless your EGTs are as wildly divergent, I suspect you have a cooling air flow problem, but first would check to make sure your readings are correct. Might try swapping a pair of sensors from one side to the other, keeping leads intact for each.

David A.

Hi David,

My EGT temps have a similar pattern at cruise, although cylinder 3 is the hottest. Again #6 is coolest.

See pic:

https://1drv.ms/u/s!Aqvegj5EiW7apjoYm_lKXX5t-tpv

I have an aeroinjector with a flow straightener upstream.

Hi Paul,

Looking at your screen shot and comparing your cht's and egt's to anything I've ever seen in operating my Sonex, I have a couple of observations. First, regarding your flow straightener.........your egt spread is greater than I would typically see without having a flow straightener. Are you confident your straightener is accomplishing anything? And, second, your cht readings are literally night and day different to anything I've seen in operating my Sonex. Are you confident that you have the cht cylinder numbers assigned properly? Typically, my coolest cylinder is always #1 and the back 2 (5 & 6) tend to be hottest in a climb while the middle 2 (3 & 4) tend to be hottest in cruise.

Hope this helps,

Art,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,,,Jabiru 3300 #261

Thanks for the feedback Art. Next time I get out to the hanger I’ll check, and possibly remove the flow straightener.

I’m blocking a lot of air from cylinders 1 and 2. Something seems to have changed though, as CHT1 was always cooler than it is now. Definitely worth doing some investigating.

I trimmed the silicone bafflingly and attached it to the out of the aluminum housing. I also trimmed some of the aluminum that I have in front of cylinder 1. As you can see in the picture, cylinder #1 is much cooler.

I also attempted to block some of the air going to cylinder #6, but it’s still running cooler.

I also removed my air straightener, and the EGTs are fine at cruise, but #5 EGT went over 1400F and #3 CHT went over 356F on takeoff. I throttled back slightly and the EGT immediately dropped to the upper 1200s. #3 CHT took a little longer to come down, but a minute or so later it was around 330F.

I sure wish the fuel was atomized just a little bit better. Maybe an aero injector with 2 needles?...

https://1drv.ms/u/s!Aqvegj5EiW7apjvZzdaUaYXTulgd

Paul,

I share your wish to have more even fuel distribution to all 6 cylinders, but with the stock Jab manifold, this just isn't likely to happen, despite the carb. You temps actually look pretty good, and certainly in the ballpark of other Jab Sonex I've seen.

Remember, with the AeroInjector that last little bit of throttle movement gives a slug of fuel and almost no additional air to go with it. If you throttle back say 1-2 mm from WOT and the EGTs get lower, you may actually be burning too much fuel at WOT and excess (unburned) fuel is still burning in the exhaust manifold which is what's causing your high EGTs. You might try this at altitude in conjunction with the mixture knob and see if that's happening. (It's unnerving to do this, but at WOT try leaning just slightly and see if the EGTs drop slightly - that will tell you for sure.)

Jeff