Lean of peak in a carbureted O-360

[Ron Lee]

Today I decided to try to run lean of peak in my newly rebuilt O-360. Normally I run EGT at 1330 degrees F. At 13,500' I continued to lean it until it peaked around 1400 degrees then started dropping. Around 1340 degrees lean of peak I noticed a slight loss of power then the typical roughness.

Fuel burn at lean of peak was around 7.3 gph and 8.5 gph at 1330 degrees rich of peak.

What probably made this possible was the flow matching done by Ly Con.

[gmcjetpilot]

Lean of Peak on one jug? What where the other cylinders doing? (EGT to Peak spread for each cylinder respectively)

You say it was rough? " I noticed a slight loss of power then the typical roughness" So it sounds like you where 60F LOP? That is pretty good if you got that far before roughness.

The FI allows the spread to be tighter making LOP more practical. You can do it with a carb, its just not easy. If you can get smooth lean of peak, where all 4 cyl are LOP say 20F or more, that is great. Who said flow matching did not work.

[Ron Lee]

I still need to update to four cylinder CHT and EGT monitoring. I believe that previously to the rebuild the "lean to rough then enrichen til smooth" happened rich of peak.

[gmcjetpilot]

Originally Posted by Ron Lee

I still need to update to four cylinder CHT and EGT monitoring. I believe that previously to the rebuild the "lean to rough then enrichen til smooth" happened rich of peak.

Still if you are getting 60 F LOP before rough you are doing really well.

[petehowell]

Here is a flashback to my early testing:

http://www.vansairforce.com/communit...5&postcount=27

Here are the graphs:



Here is a picture of the Dynon EMS - It pukes data right in to my laptop. The LEAN MODE shows degF LOP.



Finally Dynon showing 30.6 mpg!:

[AlexPeterson]

Originally Posted by Ron Lee

Today I decided to try to run lean of peak in my newly rebuilt O-360. Normally I run EGT at 1330 degrees F. At 13,500' I continued to lean it until it peaked around 1400 degrees then started dropping. Around 1340 degrees lean of peak I noticed a slight loss of power then the typical roughness.

Fuel burn at lean of peak was around 7.3 gph and 8.5 gph at 1330 degrees rich of peak.

What probably made this possible was the flow matching done by Ly Con.

Ron, be sure to study what Pete has written on carb'd engines and fuel air mixture distribution, it is good stuff.

7.3 gph at 13,500' indicates that most cylinders are still quite ROP. Was your MP around 18"? It could be that, if you are monitoring only one cylinder's egt, you happen to be monitoring the one that leans first. Just for a data point, 7.3 is my fuel burn at about 22", 2350 rpm when running all four cylinders about 30 to 50 F LOP. I would expect around 6 gph at that altitude.

Monitoring all four egt's and doing work like Pete has done will pay for itself in short order with gas at 4 bucks.

[Ron Lee]

Alex, you may be right. I am seeing higher fuel flow numbers compared to before the rebuild but I now have 9.5:1 compression pistons which may account for much of the increase.

I just read Pete's link and see that he has a carb too. The difference is that I was not using carb heat although that will be tested once I get all the probes in to monitor things better.

I will have to record and plot things by hand.

[Ron Lee]

I did another test flight and recorded data. It is not as promising as the first try. Fuel flow is a real-time mental averaging since it fluctuates on my RMI unit. Looks to me that around peak EGT is best. Flight was at 13,500' using the COS altimeter setting. Density altitude not recorded.


Lean Point / EGT / CHT / Fuel flow / IAS / RPM / MPG

1 1322 335 8.9 162 2720 18.2
2 1349 335 8.5 161 2710 18.9
3 1384 336 8.2 164 2710 20
4 1411 336 7.5 162 2700 21.6
5 1405 322 6.9 157 2620 22.7
6 1358 310 6.5 148 2520 rough

[petehowell]

Hi Ron,

I assume this is at WOT. If so, try adding full carb heat and just pulling the throttle off the full open stop, and then leaning. When it gets rough, move the throttle back and forth slowly to see if you can get it to smooth out. On mine, when I get it smooth, any movement of the throttle, fore or aft will make it run really rough. This leads me to believe that the carb heat aids in vaporization of the fuel and the cracked throttle adds some turbulence to the mixture. I can find a "happy place" where it runs well LOP. I had to experiment to find it, but it is highly repeatable.

I usually run in the 7500-11000 ft range. Good luck - keep posting data.

[gmcjetpilot]

Originally Posted by petehowell

Hi Ron,

I assume this is at WOT. If so, try adding full carb heat and just pulling the throttle off the full open stop, and then leaning. When it gets rough, move the throttle back and forth slowly to see if you can get it to smooth out. On mine, when I get it smooth, any movement of the throttle, fore or aft will make it run really rough. This leads me to believe that the carb heat aids in vaporization of the fuel and the cracked throttle adds some turbulence to the mixture. I can find a "happy place" where it runs well LOP. I had to experiment to find it, but it is highly repeatable.

I usually run in the 7500-11000 ft range. Good luck - keep posting data.

I wounder if there is any "TUNING" we can do to the plenum entrance or runners to balance them? I hate the idea of loose parts bonded or bolted in the intake for obvious reasons.

You see the TV commercials for the "tornado", some magic thing you buy for a car to put in the intake, to increase gas milage. They are of course a rip-off, but wonder if there is some plate we can bolt between the Carb and plenum to produce turbulence (better fuel mixing) or vary the bias between the runners (fwd/aft cylinders) to reduce the "Gami Spread".

On another thread a Gent found after getting his cylinders flow ported by Lycon he was able to run LOP or much leaner with smooth operations. It's like LOP with FI, it is going to take some messing around to get it to balance out.