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I have a '56 PA22-150 with Lycoming O-320 A1A. I'm trying to figure out why my CHT temps. and their respective delta T's in cruise are so disparate.
Before I lean out aggressively, I typically have 60 to 70 degrees F CHT difference in temps from #1 (~315 deg F) to #4 (~385 deg F). Some say it's baffle config. Some say it's carburetor details. Some say it's both. Please reply.
Several factors are involved in the CHT difference between cylinders. Proper baffling and airflow considerations are a major part of the equation however it is seldom just one issue. Things to look at. Intake leaks, throttle position, mixture (overly lean or rich), is the carb correct for the sump, are you trying to climb out at partial throttle, leak in primer line, missing baffle plates between cylinders, Timing advance with electronic mags. The list is not complete just some things off the top of my head. Use a flashlight and look at all your baffling from the front for holes. Open the cowl doors and you should see witness marks from the baffling on the underside, any gaps is a place for air to bypass the baffle. What temps on what cylinders do you usually see in level flight at 2400 RPM full rich? What happens to them with a full throttle climb at 500 fpm? What are the temps after you lean aggressively? 1,000 ft asl? What is your fuel burn at 2400 RPM full rich. What is RPM drop with full carb heat at 2400 rpm full rich? What is EGT change for full rich to first cylinder going lean of peak? What pitch prop do you have? Lots of questions but trying to figure out a problem on a keyboard without some baseline info is hard. Post pics of the baffling.
DENNY
The O-320 has different length intake tubes so some of the temp differences is in the design. Also the baffles, we have used foil tape to partially block off the front of number 1 and 2 cylinders to even the CHTs out. The 10-5217 carburetor flows less fuel but atomizes the fuel better so all cylinders get better distribution than the old 10-3678-32. Lycoming list that carburetor in their service instruction on replacement carburetors. It has been proven on the test stand at LyCon. Similar to installing the peppered fuel nozzle in the -32 carburetor to help cool the O-340 on the Carbon Cubs.
Some of the differences between 10-3678-12 and -32 and 5-6200 carbs are addressed. I've also read SB-22 which explains replacement of the fuel nozzle to a #47-862.
Now we can add the 10-5217 carb to the mix.
First question: If it's not listed on my '56 PA22-150 TCDS, how do I find a complete list of all acceptable carburetor variants that are legal to be installed on my plane? Right now, my TC just shows the 10-3678-11, -12, -32.
Second question: Why are there so many carb variants that are acceptable to be installed? Different missions? Different intake manifold designs? Different carb airbox designs? Was Piper just experimenting back in the day?
I'm obviously looking for the most power and efficiency (low fuel burn), and low delta-CHT temperature splits, that I can reasonably achieve.
I started down this road because my I thought CHT splits were high. Talking to Tim Henderson at MSA in Gibsonville, N.C., he says 50 to 75 deg diff. on CHT's isn't a big deal. Ok, but some people get these numbers down to 20 or 30 degrees in spread. He made some good recommendations regarding looking at my primer circuit leaking, leaks in intake manifold rubber junctions and gaskets, etc.
I'm going to also evaluate my baffles and play with partially blocking off number 2 a little more, and get my carb updated.
Because of our wide temp swings I spent a year and a half working on the proper blocking tape size for the front cylinders. Once I had the working well I made ramps. I have seen the fuel nozzle used in a 32. It did help with distribution but needed to be drilled out with a number 29 drill bit to flow properly, that carb also had a polished one piece venturi and carb throat so that may have effected the need for drilling.
DENNY
The 10-5217 is the latest carb that Lycoming recommends for the O-320. The 10-3678-32 was a fix for the Apache running lean on cold weather at altitude. Lycoming approves the 10-5217 even though it is not on the Piper TCDS. Would not bother me to install it with that approved data in hand.
Because of our wide temp swings I spent a year and a half working on the proper blocking tape size for the front cylinders. Once I had the working well I made ramps. DENNY
Might you have a picture or two of what you ended up with?
I've emailed both MSA and Avstar. Their responses suggest they're fairly clueless regarding recommendations of any carb for any engine. They will sell you whatever you ask for. You have to know what you want. So, I'm wondering if I should ask Lycoming what they recommend.
After 65 years, there are no indications in my logs that the carb was ever overhauled. I have to think it must have been, but I can't find any records.
I'm inclined to go with the 10-5217 since, as Steve P. pointed out, it is Lycoming's latest recommendation for the O-320.
To recap for those that don't like to back-read strings and might just be tuning in:
I have a 10-3678-11 carb on my O-320 A1A, and it sounds great. Runs great. But my Cylinder head temp splits are somewhat large at 70 to 80 deg between 1 and 4 cylinders, before I intercede and do significant leaning. I'm looking for lower temperature differentials between cylinders, and of course anyone would like lower fuel burn rates and more power...
I'm also messing with cylinder dams/ramps on the drivers side (#2) to get more air to cool number 4.
CHT delta T's and Carb type details
Originally Posted by PACERGUY
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