Horsepower for Weight.

[Snowbirdxx]

Another interesting fact is that the Lyouming oilpaan, where the bell type carbinlet ends, is a flat plate. The Superior pan has a conical bump there which should help the upstram carblow to be routed into the cylinger needing fuel. I have the Superior pan on my spare engine.

 

[Clifford]

Genuine question…does your conclusion (not designed to cruise WOT) really follow the premise regarding the enrichment circuit? How does the red knob play into this?
My plane is FI and I’ve forgotten.

Hi Jeb,
The enrichment circuit / WOT thing is what I read in a description of the carb. As I recall it was an attempt to "help out the pilot". I found a couple (or few?) articles on the carb and don't remember which one put it in these terms.

 

[Clifford]

Why are you stressing over EGT instead of CHT?

Hi Jack,
First off, yes, our airplanes work as-is. But I like fiddling with things when I think I see something better.

I see an EGT delta of between 150 - 200 degrees. In my mind that's a ton. Further, #1 EGT is always the hottest by somewhere between 75 - 125 degrees. And with 400 hours on the engine #1 cylinder compression test is already down compared to all the others. For me all of this points to the prospect that something could be better. That's all.

 

[JACK]

Clifford,
Do you have a 4 probe CHT? If so how much spread between them? I guess my question is "isn't CHT a better gauge than EGT?"

 

[dogday]

Jack,

In simplified terms, CHT is a function of both the internal engine combustion process as well as the cylinder head's external cooling effectiveness. If cooling air flow around the cylinders was balanced with perfect symmetry, then the variability in CHTs between cylinders could be a good reference/indicator to look at the variability in the combustion process between cylinders.

Provided EGT probes are positioned correctly, external factors under the cowl have a small effect when looking at EGTs to determine internal combustion variability between cylinders.

 

[JACK]

Understand, Thanks for the explaination.

 

[belloypilot]

Jack,

In simplified terms, CHT is a function of both the internal engine combustion process as well as the cylinder head's external cooling effectiveness. If cooling air flow around the cylinders was balanced with perfect symmetry, then the variability in CHTs between cylinders could be a good reference/indicator to look at the variability in the combustion process between cylinders.

Provided EGT probes are positioned correctly, external factors under the cowl have a small effect when looking at EGTs to determine internal combustion variability between cylinders.

Isn’t it more reliable to determine the fuel flows where each cylinder reaches peak EGT and work to reduce the spread (GAMI spread, as some call it) rather than trying to balance the measured EGTs? If, hypothetically, all cylinders were reaching peak at nearly the same fuel flow at a given MP and RPM wouldn’t that tend to indicate balanced F/A ratios regardless of what actual measured EGT values were?

 

[Clifford]

Dogday, Jack, and Belloypilot ..... Hi !
I've checked EGT probes (thermocouples) for relative position and calibration. Agree totally that EGT is not an accurate metric in absolute terms but in relative terms I see it as an indicator. My CHT's are relatively even and stable with roughly a 40-50 degree delta between them. I'd like better but they do also follow the EGTs.
Belloypilot, you make a good point and no I've never followed which cylinder peaks first etc. In actuality I rarely lean because I'm trying to manage the one EGT to stay below 1400 and don't have the bandwidth to lean.
A while back Thomas suggested the pushrod lengths on the hot cylinder could be too long. I would never have come up with this on my own and am in the middle of checking it now (we have a week or two of lousy WX so no flying). I'm doing the "dry tappet check" and have gaskets and retainers on order so it will all go back together with new pieces. I'll post results of the clearances when I have them.
If I find a "smoking gun" with this I can move on. If not I'm back to the airbox

 

[belloypilot]

I think the GAMI lean test is useful in any case. It should tell you if you have an imbalance in f/a ratios and that might be a different problem to solve versus an imbalance in total fuel+air charge going to each cylinder. Bonanzas, for example, have a significant flaw in the induction system that results in less air reaching cylinders 5 and 6 than 1-4. Tuned fuel injectors can solve the problem of imbalanced f/a ratios but can’t change the fact 5 and 6 make less power because they receive less air. I know an O360 in a Husky is a totally different beast but I’d think narrowing down the nature of the problem is still useful. Thanks for sharing this story with us. It helps everyone.

 

[Clifford]

Update:
I checked the "dry tappet clearance" on the offending hot cylinder (#1) and all is nicely in the middle of the spec tolerance.

So now I'm back focused on the airbox.

 

[bcone1381]

Post #49 is right on. When power is less than about 65% power, lean it and watch the EGT's peak. The first cylinder to peak is your leanest running cylinder. Wright down the FF when it peaks, then continue leaning. When the second cylinder peaks, write that FF down, then do the same for the 3rd and 4th. The Gami Spread is the spread fuel flow reading spread between when the leanest and richest cylinder reached Peak EGT. Note, EGT's are notorious unequal but the Fuel Flow when the peak is a reliable reference point.

If you mess with your throttle plate position and your Carb Heat, you can discover a spot where the spread is minimized and that means each cylinder's mixture is close to each other. A near zero spread is ideal.....a good gami spread is when you can achieve less than 0.5 gallons per hour.

 

[Ian Sage]

. . . checked EGT probes (thermocouples) for relative position and calibration. . .

If the installer left enough service loop length in the thermocouples you can also try swapping probes between cylinders 2-4 and 1-3, then running the lean test again. Record the results and compare them to the original test (keeping in mind that the gauge is representing #2 as #4 and so on). As an example, if switching the probes caused #2 to instantly display 50° hotter and #4 to display 50° cooler than the previous test then you have identified a 100° indication difference between the probes. This is a "fairly" simple way to identify any variance in the calibration of the probes themselves or their position, thus eliminating unexpected indication error from the troubleshooting process.

 

[dogday]

I saw an interesting discussion on carbs where their points made regarding the booster could put someone on the path to help correct the uneven mixture delivery between the front and rear cylinders on the o-360.

Marvel -Schebler may have already optimized their booster, but I suspect that there is a bit of room for improvement.