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Steve Brown

Well Known Member
Running LOP with O-320

I have an RV9A with an O-320, high compression pistons, and electronics ignitions (E-Mag/P-Mag). Fixed pitch prop. I have a switched 4 potion EGT & CHT.

I seem to have a peak EGT of about 1350 during cruise. I've been leaning to about 1300, but my fuel flow seems a lot higher, near 9 gal per flight hour, than what I have seen others bragging about.


I've read all (I think) the posts on this site about leaning. One that stuck out was apparently a lycoming recommendation to lean until engine rough, then enrich until smooth.

I tried it a little on my last flight with interesting result:
-The engine never did run very rough, until it was ready to die. I attribute this to the electronic ignition. I had to pay close attention to find the spot.
-When I performed this procedure, the highest EGT was about 1275, and was LOP. I didn't check to see if all EGTs LOP, but I think not.
-EGTs were grouped closer than they ever have been before.
-CHTs were all below 350.

I don't know the fuel flow, because I don't have a gauge and it was a short flight. It was a cold day and I was running ~65% power.

Anyway, I'm curious if anyone else uses this procedure and what results they have had.

My thinking is that if the EGTs are relatively low and the CHTs are low, it must not be hurting the motor.

Am I missing something?
 
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Steve Brown said:
I have an RV9A with an O-320, high compression pistons, and electronics ignitions (E-Mag/P-Mag). Fixed pitch prop. I have a switched 4 potion EGT & CHT.

I seem to have a peak EGT of about 1350 during cruise. I've been leaning to about 1300, but my fuel flow seems a lot higher, near 9 gal per flight hour, than what I have seen others bragging about.


I've read all (I think) the posts on this site about leaning. One that stuck out was apparently a lycoming recommendation to lean until engine rough, then enrich until smooth.

I tried it a little on my last flight with interesting result:
-The engine never did run very rough, until it was ready to die. I attribute this to the electronic ignition. I had to pay close attention to find the spot.
-When I performed this procedure, the highest EGT was about 1275, and was LOP. I didn't check to see if all EGTs LOP, but I think not.
-EGTs were grouped closer than they ever have been before.
-CHTs were all below 350.

I don't know the fuel flow, because I don't have a gauge and it was a short flight. It was a cold day and I was running ~65% power.

Anyway, I'm curious if anyone else uses this procedure and what results they have had.

My thinking is that if the EGTs are relatively low and the CHTs are low, it must not be hurting the motor.

Am I missing something?
Click to expand...


High Compression .... as in 8.5, 9.0, 10.0?

9 gph ff based on used over time ? Not much use. Need ff gauge.

Without a ff gauge, Alt, temp, MP, Rpm, and a power chart it would be difficult for anyone to answer your question.
 
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More info

Since this technique was intended for those who typically don't have fuel flow or MP, I'm not sure why it can't be answered without those. Two questions:

-Have you done it, if so, what happened?
-Can you harm the motor with leaning even though EGTs and CHTs are low?

Here's the details I have:

9:1 compression.

I try not to run the engine continuously above about 75% original horsepower, which I assume to be about 70% of current HP. I have a MP & OAT gauge which I use in conjunction with RPM to set power. Its fixed pitch, so these all vary significantly depending on altitude & temperatures.

Lacking one from the "factory", I made up my own power schedule. It assumes 100% power at 29.92 MP, 2700RPM, 15C. HP proportional to RPM and MP, and inversely proportional to OAT in Kelvins. This assumes flat torque over a range or 2500-2700 RPM, which I'm guessing is close enough to true.

At above about 10k, I tend to run full throttle, unless the OAT is below standard. Below that I set power for about 70%.

The fuel burns I'm seeing are over 2-3 hour flights at probably 65%-70% original HP. Ya, it includes climb, etc, but takeoff-to-touchdown fuel burn is what I am concerned about anyway.

A fuel flow gauge is one of the things on my buy list, but it hasn't happened yet.
 
IMHO you are right in your assumption that EGT's @ 1275F, and cool CHT's below 300 will not hurt your engine. I believe you were running LOP at that setting, and you were burning considerably less than 9 GPH. LOP is a good place to be for fuel economy and engine longevity, but you'll need to bone up on the proper techneques and theories behind it.

You are lucky. It is uncommon that a carburated 4 cylinder is balanced enough to run LOP correctly. My 0-360 Slicks X2 would never run LOP right. I think the mags are helping you alot in this situation.

As a rule of thumb, your EGT's should all be within 100 degrees F. CHT's within 50F. Your EGT's should be 50 degrees lower than your highest peak EGT. But keep an eye on them all!

***************

Good luck. Keep us posted. Only a FF gage will confirm the economy, but I'm sure you would be surprised.

Here is some great info on Leaning. ROP, LOP, it has it all. Fill out the form and they will mail you a hard copy, or down load the PDF and keep it for future reference on your puter.

http://www.buy-ei.com/The_Pilots_Manual_by_EI.htm

Here is a link to an "inexpensive" FF guage. I know you can find your own, but I just happened to be looking at them for a plane I'm working on. I'm leaning towards the Dynon 20 EMS, but it is alot more.

http://www.aircraftspruce.com/catalog/inpages/fuelmizer.php
 
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Steve,

My set up is similar to your's, but on an RV-6A and with only one E-mag. My average fuel burn when running WOT at 8K ish is around 9 gph. You really need an FF gauge to make any sense of that reading. Comparing EGT numbers is always difficult as its tricky to calibrate the installation and distance of the probes from the exhaust port is a factor (and that is a builder decision). I'm assuming that you have an analog gauge that you switch between pots? Difficult to assess when one pots has gone past peak and to assess is you are running LOP. The EGT numbers seem low - I can see up to 1420F, but I can also see wide variations (200F) between pots - but absolute numbers don't always mean that much. I just about always run WOT above 6K - why not, gas is not that expensive. I can run LOP but only do it on long trips and it is difficult to get all cylinders past peak, yet the engine still running smoothly - I'm assuming the leanest is getting too lean and running a bit roughly. I agree that EI is a great help in getting a carbed engine to run LOP.

When you lean do you get an rpm rise? Try leaning from full rich until the engine dies from 2000' up to 10000' and note the behaviour. Many O-320s run too lean when installed in RVs and need a larger main jet, at low level you should see a 200F rise in EGT as you lean.

I fitted a Grand Rapids EIS 4000 and am very glad I did. Probably doesn't matter exactly what you go for, but a good engine monitor with fuel flow is a real asset. I had a JPI EDM in a certified airplane and really like that also.

I don't think you will be hurting the motor by leaning at the conditions you mention. If I'm not running WOT I lean aggressively at any altitude. At lower alts, especially when its bumpy or I'm on a short trip, I just lean until first sign of rough running then richen slightly.

Pete
 
Low EGT peaks

"The EGT numbers seem low - I can see up to 1420F, but I can also see wide variations (200F) between pots"

I think the low peak EGT (~1350) are due to the HC pistons. When I put HC pistons in my Mooney, EGTs dropped about 100F.

Another post I read on this site indicated that the power produced by the engine is proportional to the difference between peak combustion temperature and exhaust gas temperature. That makes intuitive sense to me. Since higher compression results in more efficient power production, I'm assuming that is driving the EGT difference between lower and higher compression.

I could be wrong on the cause, so that is my explanation to myself rather than a strong assertion.
 
Some more LOP data points for O320

Recently I had noticed I can routinely run LOP with no problems at lower altitudes at about 22" MP.

Last weekend I did a trip down to SMX from PAO and back. Down at 7500, back at 8500.

On the way there at 7500 I ran 22" MP, which was about 1" below full throttle. TAS about 158. Perfectly smooth. EGTs reasonably well balanced with highest at 1300. CHT's well balanced with top at about 360.

I tried it on the way back at 8500 at 22" which was full throttle. This did not work out well at all. I had a real hard time finding what I thought was the right operating point. By the time I did, my max EGT was 1300, but the min was under 1200. The cooler cylinders were running so lean I could hear them periodically cutting out. CHTs were low, but not well balanced

I backed off 1" MP and used the same procedure I have been using and everything was ok. EGTs, CHTs, and TAS similar to the 7500 operating point. I ran the rest of the way home like that.

As stated by several on VAF in the past, my conclusion (so far) is that running partial throttle causes some turbulence resulting in better balance between cylinders. If this is the case, I'm thinking I can run LOP at any higher altitude, as long as I back off from full throttle a bit. Maybe it will take less than 1" at higher altitudes????

I have vans gauges with a switch, so it is possible that I just screwed up the procedure at 8500. I've got a couple of 4 channel temp gauges on order from MGL and I'm hoping that helps me make better sense of settings.

Round trip fuel burn was 8GPH using GPS flight time.
 
Steve Brown said:
I tried it on the way back at 8500 at 22" which was full throttle. This did not work out well at all.
Click to expand...

Hey Steve,
Try a little carb heat at full throttle and see if that helps with the leaning. Some people reported that using a little carb heat evened out the temps on their planes.
 
LOP with Carb

Steve,

Here are some of my results from an old post. Now that Dynon TAS is working, I see see 150KTAS on about 6GPH - that is instantaneous, not overall for the flight. I run a CS prop so that will be diff from you.

Good luck - LOP is worth chasing.
 
Given the design of Van's FAB, I'm doubting that partial carb heat will do anything for you. In a Cessna 150/172/182 box, it will work a bit better, because there is less resistance in the path of the Carb heat air, but being that both heat and cool air are filtered in the Van's box, the path of least resistance would be the cool air, and the heat really doesn't do anything until it's full on.

My 2?
 
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