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EGT spread for correct jetting

O

Oliver

Registered User
Breaking in a new 160 hp o320.
battling high temps, done about every trick I could come up with.
ruled out intake leaks, baffleing etc

Looking at jetting next:
egt full rich to peak temps while gradually leaning at 2000'
60deg day:

2200rpm 122deg spread. (1298-1420)
23 106. (1343-1449)
24. 80. (1362-1442)
25. 70. (1400-1470)
26. 49. (1439-1488)
 
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Nothing wrong with those numbers for a carburetor engine. While leaning does the EGT rise and then fall? It should. Are you able to cruise with your CHTs remaining below 400? Not much over 400 during full throttle climb. If so, just go burn gasoline.
 
2300 400deg level 2000' 60deg oat Cyls 2-3-4, 1 is 380
full throttle operation- 450 and off the chart if I don't pull back
 
Oliver said:
2300 400deg level 2000' 60deg oat Cyls 2-3-4, 1 is 380
full throttle operation- 450 and off the chart if I don't pull back
Click to expand...
Climb up to 5000 and check the temp spreads at full rich to peak at max (green) RPM.

My my engine is similar but not new but I can't run full throttle in level flight, At 2400-2450, I see 380-390/1360-1380 hottest down low full rich in similar conditions. Thinking about changing to Sutton exhaust to cool it better and even it up a bit more, up high, no worries.
 
One of the locals dropped by this afternoon, bragging about his new engine monitoring equipment - list price four grand before installation. He says that his IO 360 went from 10 GPH to eight, and says that GAMI will calibrate his injectors for another gph - down to seven gph on a 200 hp Lycoming!

If I start to believe that I shall convert the Super Dec.
 
Go get your engine warm and get into a stable cruise. Push to full rich and let it stabilize. Look at your Hottest EGT temp. Now lean until you get the first hint of a stumble. How different is the temp? I was taught that 100* change was bare minimum. 150* is better. If you get 150* change you aren't jetted too lean. Temp spreads between cyls are a different issue. I like more than 150* leaning authority because I fly in winter and cold temps require more fuel. I can always use mixture to reduce summer fuel flow. Talk to several guys and you'll get several opinions. I never get tired of this topic.
 
To clarify:
at 2300 rpm level flight 2000agl full rich 1343deg egt, start leaning to peak 1449.
thats a spread of 106deg, not the desired 150

higher power settings things get progressivly worse.
2600 rpm full rich 1439, peak 1488, that's a 49 Deg spread not the desired 150

im assuming I have a fuel flow issue, no? Either carb jetting or otherwise.
 
As per lycoming recommendation . "Peak power" is obtained by mixture setting 100 Deg rich of peak. (EGT)
 
Oliver, here's a photo of my Cessna's carb bowl that shows the main jet. It's the brass pipe in the middle. The slotted fixture above is the mixture adjuster. It fits into the jet inlet port and rotates to allow full flow or restrict the flow. Pretty simple, at least in the bowl end of things.
IMG_0104.jpg
 

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Do you have a fuel flow instrument? Compare gph at take-off power to Lycoming specs or to other users of similar engines. If you take off with low fuel flows your CHTs will get hot and stay hot. The take-off flow rate is an important value in this discussion.
 
Yes on ff. Still working out K factor though.
think marvel carb has an enrichening circuit
at WOT operation. Might relate, but to preserve sanity, I'm focused on what's happening
at high cruise power settings right now.
 
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