LOP in Carbureted Engines

Over the years, we have had difficulty operating carbed engines LOP for only one reason--they historically have poor F:A ratio balance. Even TCM and Lycoming have said that Cabred engines can't be run LOP. That is true if one assumes that you cannot balance the F:A ratios. However, as Conusious say, "Do not tell man something impossible when he already do it!"

I have personally run many carbed engines LOP with excellent success and repeatability. I know of several hundred others who are having the same success. Here is the issue.

A carburetor atomizes the fuel into small, medium, and large droplets. These droplets weight differing amounts and take different paths in the induction system. This results in varied F:A ratios among the cylinders. If one can get the fuel droplets VAPORIZED early in their progression, the F:A ratios will be quite even between the cylinders and the cylinders will have the same F:A ratio and therefore the same Hp output and will run smooth along the entire mixture spectrum.

One method to improve this vaporization has been to **** the throttle plate slightly to induce some turbulent airflow into the induction. This has been successful in some applications and not so successful in others. As it turns out, each engine and installation has an optimum carb temp which results in maximum vaporization and minimum heat required. Once that is discovered, simply setting that Carb Temp will result in maximum vaporization and optimum F:A ratios. As soon as that is accomplished the engine will run smoothly LOP.

How to find the optimum carb temp:
1) Set the engine monitor to the DIF function.
2) Add carb heat until the DIF is the lowest number you can get with the least amoutn of carb heat.
3) Note the Carb Temp. This same temp can now be set, winter, or summer, high or low to achieve the optimum fuel vaporization.

In a C-182, this is 10dC (50dF). In a Cherokee 180, it is 40dF. In my Twin Beech, it's 35dF. Each is different, but once you find it, you have it.

If it will not run smooth LOP, you have other problems like induction leaks or weak spark plugs or other ignition issues. ANY conforming engine with good F:A ratios and a good ignition system will run smoothly LOP--or it is not conforming.

Walter Atkinson
Advanced Pilot Seminars

LOP carburated engines

Walter,

The "bad word filter" got one of your words, and it seems to be an important one.

One method to improve this vaporization has been to **** the throttle plate slightly to induce some turbulent airflow into the induction.

Click to expand...

Was that "crack"?

You also wrote:

Set the engine monitor to the DIF function.

Click to expand...

I take it this means without an engine monitor, LOP will be tricky. BTW, what is the DIF function?

Thanks!

Hot stuff

I noticed no RV numbers or examples (Cherokee and C182).

From my experience the Carb is cooking in a RV's tight cowl bolted to a hot sump of oil. Also the "standard" carb heat to the air box, even though the valve is closed, "spill-out" all over the front of the air box and front of the carb (externally). Carb temps of 80F (or more) all the time. May be at low power in the winter? The idea or running carb heat makes the mixture richer. I don't buy the temp thing, at least in a RV. C180/182 which has a cold carb? may be.

Throttle plate? I hear this for Contenentals but not Lycs. I guess the theory is the partial closure of the butterfly mixes it up better, as you say. However I KNOW it will add to "pumping loss". Meaning you will lose MAP and cause the engine to work (suck) against this restriction. The acronym TANSTAAFL comes to mind. Also you will now forward basis the fuel into the plenum towards the fwd Jugs. If the aft cylinders are lean you are SOL, the throttle plate "don't bend that way bro". The throttle plate tends to be like a hose and the BEST "balance" you can do is have it go straight (WOT), notwithstanding your MIX IT UP theory of the partially closed butterfly. I always thought of putting in some guides or vortex generator in the sump (intake plenum) just above the carb to bias the flow as needed, but the idea of parts bonded in the sump is a bad one. It just is not worth it to me. If I wanted FI I would have bought it for the extra $3,000 retro fit ($2100 if bought new from scratch).

I hear the theory and the words. " I know of several hundred others who are having the same success." 100's! I don't even know a 100 pilots, much less any running carb'ed engines LOP; not sure who these folks are, but I am not one of them Why me, why me, it's always me.

I don't worry about it, at all. I go for 75-100 ROP and try and fly closer to 55% than 75% power.

Don't take my rejection or surrendering further LOP attempts as not appreciating your excellent write up. We can talk about fuel molecules dancing in the induction and all kind of wonderful things, but the engine is not "stochiometrically" balanced any way from a hardware (mechanical) stand point. In fact it's the ability of fuel injection to provide (precision) unbalanced F:A to each cylinder to make up for these inherent shortcomings, such as exhaust. If balancing a FI was easy they would balance the injectors in the shop and be done. However with Lycs at least you have to "adjust" each based on what they are doing on the engine.

Although the classic Lycoming cross-over is pretty good at producing fairly low exhaust restriction with moderate savaging, it's far from balanced. Just measure the pipe lengths, primary and collector for each jug. Also, each cylinder has differnt cooling, compression and induction path lengths. Thus the mixture (F:A) and power is different between each cylinder. Fuel trim between jugs to balance these hardware based issues is key.

I find from my experience and your description the effort is a bit hit-N-miss with a dash of luck. Some carb engines no matter how you "crack" the throttle or cook the carb will NEVER run smooth LOP. I find your comment that if you can't get LOP operation there is something else wrong. That is a bold statement and think you would have a hard time convincing me that this is true. I think you can have a normal, healthy Lyc that can not run LOP.

My latest creation, is a RV-7 with a O-360-A1A. I'll give LOP a shot again like a true optimist, but I fully expect it to run rough before I can get all the cylinders at least 40F LOP. I'll try the throttle bump and carb heat methods, but I am lazy and it sounds like too much work.

As AC/DC said, "For those about to rock, we salute you". I say, "For those about to run LOP with Carbs, I salute you". One day the fuel atomization angels may shine upon my induction and bless me with smooth LOP operations on my Carburetor Lyc. I LOVE MY CARB IT IS STATE OF THE ART TRACTOR TECHNOLOGY. Yea Verily!

Mickey:

Yes, the word was either "crack" or "c.o.c.k" the throttle plate. It is the less desirable approach. The hot-running lycs may not need this carb heat trick until the dead of winter.

Walter

gmcjetpilot:

You didn't sign your post and I doubt that's your real name, so I don't know who to politely adderss this to, but here gos! <g>

**I noticed no RV numbers or examples (Cherokee and C182). **

There are many of those carbed engines working right. I've personally flown two different RVs and have been successful with these technics. I do not recall the optimum carb temp, so I did not post it.

**I guess the theory is the butterfly as you say mixes it all up better. However I KNOW it will add to "pumping loss". Meaning you will lose MAP and cause the engine to work (suck) against this restriction. **

If you see ANY MP change, you've moved the throttle further than necessary in my experience.

**Also you will now forward basis the fuel into the plenum towards the fwd Jugs. If the aft cylinders are lean you are SOL, the throttle plate "don't bend that way bro". **

See above!

The cylinder SUCK in what they can, unless you are supercharged, the assumed airflow in the induction is not a factor.

**I hear the theory and the words. " I know of several hundred others who are having the same success." 100's! I don't even know a 100 pilots, much less any running carb'ed engines LOP; not sure who these folks are, but I am not one of them Why me, why me, it's always me. **

Well, I visit eight other forums almost daily and have personally trained over 1000 pilots in the details of engine management. The number of a hundred is low.

**I don't worry about it, at all. I go for 75-100 ROP and try and fly closer to 55% than 75% power. **

Then these issues are not something for you to worry about. Others may have a different approach where this information is of value to them.

** the engine is not "stochiometrically" balanced any way from a hardware (mechanical) stand point. In fact it's the ability of fuel injection to provide (precision) unbalanced F:A to each cylinder to make up for these inherent shortcomings, such as exhaust. If balancing a FI was easy they would balance the injectors in the shop and be done. However with Lycs at least you have to "adjust" each based on what they are doing on the engine.**

Nope. You're confusing volumetric efficiency with F:A balance. They are not the same and are not addressed the same way. It is quite possible to balnce the F:A ratios in a poorlyvolumetirically balnced engine. It's done all of the time--regularly. Again, one should not tell another that something is impossible when he's already doing it! <g>

**I find from my experience and your description the effort is a bit hit-N-miss with a dash of luck.**

That's true if one does not have an engine monitor. Once the optimum temp is found, it's pretty consistent.

**Some carb engines no matter how you "crack" the throttle or cook the carb will NEVER run smooth LOP. I find your comment that if you can't get LOP operation there is something else wrong. That is a bold statement and think you would have a hard time convincing me that this is true. I think you can have a normal, healthy Lyc that can not run LOP. **

Could be, but so far, that's not been the case. We find LOTS of engines have insidious induction leaks that cause problems and even more have ignition issues which don't show up ROP that are a problem LOP. We've done an awful lot of research on Lycomings which seem to work fine. I can't address your particular engine.

** I fully expect it to run rough before I can get all the cylinders at least 40F LOP. **

Ah, HA! There's the problem. Why so far LOP? That's waaaay further than you need to be for anything below 75% power. At lower power settings that far LOP you will be feeling the normal cycle to cycle variability in the combustion event as roughness. Heck ,that'd be normal! At, say, 65%, I would be 15-20dF LOP at the MOST. Probably 10-15dF LOP will be good. 40dF LOP at lower power settings is leaner than BSFC(min) and there is no advantage to being that lean. There is rarely any time in cruise where these carbed engines need to be more that 20dF LOP. Being further is counter-productive.

Good luck.

Walter

I wonder if "cowflop" gets through the filter?

When your engine is at less than 75% power pull the mixture until the engine misses a little and shove it in 1/4"... then relax!

cl

Chickenlips said:

I wonder if "cowflop" gets through the filter?

When your engine is at less than 75% power pull the mixture until the engine misses a little and shove it in 1/4"... then relax!

cl

Click to expand...

Ya know....as much as I am a high-tech rocket engineer, I find that more often than not, if I do the EGT and Fuel Flow dance with all my fancy instrumentation, I end up just about at the same spot as if I did it this way.....

Lean to roughness and then smooth it out. My fuel flow then ends up within .2 gph of the "Minimum Fuel FLow" lin on Lycoming's graph, and I'm happy with that!

Still like to play with all the fancy toys when I am bored though...

I concur, so far...

So Walter?. I have an O-320, 160hp and when I am running at 10,500 or 11,500ft I ever so slightly play with the throttle to even up EGTs as close as possible. I can bring EGTs on cylinder 1 & 2 down and 3 & 4 up to within 50f of each other. Then I lean until the first cylinder peaks and that is where I run the engine.
So? if I play with the carb heat a bit it may be possible to run LOP? I was at 12,500 one day while flying off my 25hrs and I guess the conditions were just right because I was able to run LOP with no noticeable roughness and was burning about 1 GPH less. I haven?t been able to obtain that again.
Interesting post. No argument here and will let you know my results when I get a chance.


And CL & Paul you are both right on...I was lleaning the other day like I use to (by ear) and I ended up very close to the "exact intrumentation" lean.

Just having fun!!!

Roger:

At those altitudes being about 10-15dF LOP is an optimal mixture for the balance between speed and economy. As a general rule, a DIF of 50dF in a carbed engine will be adequate to work well. Each engine will be a bit different.

Walter

Almost there...

As you can see I can get EGTs pretty even when adjusting the position of the throttle plate just ever so slightly. The 1322 temp is 1 degree rich of peak the other cylinders are all running considerably more rich of peak.

I'll give it a try, We shall all see

Walter Atkinson, WROTE:

gmcjetpilot:You didn't sign your post and I doubt that's your real name, so I don't know who to politely address this to, but here gos! <g>

(Sorry it is George, I forgot)


There are many of those carbed engines working right. I've personally flown two different RVs and have been successful with these technics. I do not recall the optimum carb temp, so I did not post it.


(Look here is my going in position. LET'S SEE. It sounds like it has possibility.
Lets test it out. It will sink or fly.

Of "those carbed engines", I assume we are talking O320/O360 lyc's not 6
cylinder Continental? 6-Cyl's are inherently more suitable for LOP operations.
Past LOP small changes in mixture equal large power change. 6-cylinder
engines are more tolerant to variations between cylinders, so it has the
ability to maintain reasonable smoothness, even with small "Hiccups".)


If you see ANY MP change, you've moved the throttle further than necessary in my experience.


(Yes I know, now we both know we both know. However any
restriction, even though you don't see it on the MAP gauge is a loss.)


See above! The cylinder SUCK in what they can, unless you are supercharged, the assumed airflow in the induction is not a factor.


(Makes no sense, sorry, its a non-sequitur, supercharged and volumetric
efficency? On 200 mph RVs with very low restriction induction we are seeing
1" more than a typical Cessna or Piper design, in part due to speed. However
again it's not really relevant, except possibly for the air box.

The airbox design determines the air flow going into the Carb's venturi. Van's
standard airbox's FAB-320 and FAB-360 are pretty good. However there will
always be some turbulence going into the Carb. This can play a little havoc
with F:A balance. Just a thought.)



Well, I visit eight other forums almost daily and have personally trained over 1000 pilots in the details of engine management. The number of a hundred is low.


(Wow that is impressive, really I believe you; Where do you teach all these
pilots? That is a lot. What are the other forums where folks are reporting LOP
Ops in 4-cylinder Lycs with Carbs? I hate to focus just on 4-cyl Lycs, but
that is all I care about. Forget C182's, sorry. I would like to read there
experience. )


**I don't worry about it, at all. I go for 75-100 ROP and try and fly closer to 55% than 75% power. **

Then these issues are not something for you to worry about. Others may have a different approach where this information is of value to them.


(The whole POINT of LOP operations is fuel economy. Right? So there are
easy and reliable ways to achieve fuel economy without LOP. Just my
opinion, and I am not trying to steal your thunder, and it is not a WORRY to
me. I am passing on what I think is valuable useful information others can use
from 12,000 hours of flight time. It's just a statement of my "philosophy" and
opinon about engine management. This DOES not mean I don't think your
comments have value. In fact I want to try them. However I KNOW what I
suggest WILL WORK 100% OF THE TIME ON 100% OF AIRCRAFT, requiring no
special skills, instrumentation or technique. In the end I can approach the
same MPG. With a little O320/360, LOP savings are not what they would be in
a IO540.

I am not trying to distract others from the enjoyment about the information
you provided. We are all big boys and girls and can make up our minds.
When "we" start getting 100's of post HERE from RV'ers saying "HEY IT
WORKED, I GOT LOP WITH HEAT AND A CRACK", we will all know. Than
everything I say is MOOT. This is simple procedure to test, so lets test it.)



Nope. You're confusing volumetric efficiency with F:A balance. They are not the same and are not addressed the same way. It is quite possible to balnce the F:A ratios in a poorly volumetirically balnced engine. It's done all of the time--regularly. Again, one should not tell another that something is impossible when he's already doing it! <g>


(Nope I am not confuse at all. You brought up volumetric efficiency (VE). I
am taking about EVEN power pulse from all cylinders, REGARDLESS OF VE or
MIXTURE. Lets focus on the balance alone and keep it simple. Really a
O320/360 Lyc is like 4 single cylinder engines that happen to share a crank,
accessory case and carb. That is a simplification but you get my point. A 4-
cylinder engine is already at the edge of reasonable smoothness. With LOP,
once you go past peak a small change in F:A mixture makes a big differnce in
power. That MEANS there is a very narrow EGT spread. Reading the other
post 50F EGT delta is not going to hack it. To get LOP carb is possible, and
you say so, but I have not tried the CRACK / HEAT method.)


**I find from my experience and your description the effort is a bit hit-N-miss with a dash of luck.**

That's true if one does not have an engine monitor. Once the optimum temp is found, it's pretty consistent.


(I'll try it, but I have to be honest, I sincerely don't think it will make a
differnce because the temp is already hot. However may be adding the heat
a little up stream, as you suggest will help. I am a GOT TO SEE IT TO
BELIEVE IT Guy. One thing for sure, you will lose more power due to less air
density. Also despite your claim there will be no loss on MAP, I say there will
be, it just may be small. This brings me back to just fly at low power settings
and lean 75F ROP, no special technique or instruments needed.)



**Some carb engines no matter how you "crack" the throttle or cook the carb will NEVER run smooth LOP. I find your comment that if you can't get LOP operation there is something else wrong. That is a bold statement and think you would have a hard time convincing me that this is true. I think you can have a normal, healthy Lyc that can not run LOP. **

Could be, but so far, that's not been the case. We find LOTS of engines have insidious induction leaks that cause problems and even more have ignition issues which don't show up ROP that are a problem LOP. We've done an awful lot of research on Lycomings which seem to work fine. I can't address your particular engine.


(Well I have to try it. I have an open mind and admit I never went thru
the "procedure" you suggest. I don't think it can hurt as long as the engine is
accurately instrumented and well below 75% power. BTW, who is the "WE" in
this Lycoming reseach think tank? Sounds like fun. Is this a school or
government funded organization. May be Cafe foundation ORG should look
into this? )



** I fully expect it to run rough before I can get all the cylinders at least 40F LOP. **

Ah, HA! There's the problem. Why so far LOP? That's waaaay further than you need to be for anything below 75% power. At lower power settings that far LOP you will be feeling the normal cycle to cycle variability in the combustion event as roughness. Heck ,that'd be normal! At, say, 65%, I would be 15-20dF LOP at the MOST. Probably 10-15dF LOP will be good. 40dF LOP at lower power settings is leaner than BSFC(min) and there is no advantage to being that lean. There is rarely any time in cruise where these carbed engines need to be more that 20dF LOP. Being further is counter-productive.


(Ah HA! The EGT spread is too great to get them all LOP without severe
misfire and roughness. Ah, HA! back at you. The 40F LOP I mentioned is
optimal or max, however with EGT spread, one or more cylinders will be at
40F LOP (or more) wheather you want it or not. 10-15F LOP, however is
HOT. I would like 20F LOP or more. I know on the LOP side is way cooler than
the equivalent EGT spread to peak on the ROP side, however that is why I
run 75F ROP and not peek, but I'll give the carb heat and throttle "CRACK" a
try. I just don't run engines at or near peak on either side. Sorry I'll burn a
little more gas first. No actually I take that back, I will just fly at lower power
and save gas. LOP does make less power and speed. TANSTAAFL.


BOTTOM LINE LOP IS NOT SUITABLE FOR ALL ENGINES, AND IT IS NOT A
MAINTENANCE PROBLEM.)

Walter

Cheers George

gmcjetpilot said:

Also despite your claim there will be no loss on MAP, I say there will be, it just may be small.

Click to expand...

George, even if there's a 0.2" MAP loss by using the c.o.c.k-the-throttle method (I'm not suggesting that there would be, just making the point that perhaps you personally would see a measurable drop in MAP), would you rather have that 0.2" of MAP back and run unbalanced, or lose that tiny bit of power and run balanced? Regardless of ROP vs. LOP, wouldn't you agree that even F:A distribution is somewhat important to your engine's wear & tear?

Pass the popcorn

Mike

I'll take mine with butter

Gosh, I almost really hate to get involved in these posts any more. Can?t we have differences in opinions without step by step rebuttals?
Instead of bla bla bla, go out and fly and get the numbers.
I have over a 1000 hrs and have been in the business over 30 years and I?m always open to new opinions. That?s what is so neat about these threads. If you like it go try it if you don?t like it?then don?t try it. I just can hardly bring myself to read these; I said? you said?that?s not what I said?I?m smarter and more eloquent than you overindulgent ramblings anymore. WHO CARES?
And that?s my opinion for what it?s worth.

And Dan

Even fuel distribution is important and I can not see any difference in map with the slight throttle movement necessary to even up EGTs. Even running at peak this way is best practice. If you can get LOP then more power to you, (or less power to you).

Free Consulting

Walter

My ignition advances to about 40 BTDC under low manifold pressure. How would you guess that would affect the optimum lean of peak position - say at 55-65 %. That is, if I were to run at something more than slightly LOP (say 50 degrees), might I see yet lower specific fuel consumption. Intuitively, it seems to me that I could optimally run further LOP with more advance available. Thought your experience with your version of the FADEC (PRISM?) might allow you to answer that question.

With two Jeff Rose ignition systems, I can easily run smoothly, though at greatly diminished power, to 100 or more degrees LOP. I had a fuel filter slowly clog on a flight and noticed that I was down to 5 gph wide open throttle at 8000 feet. Still smooth. Great units. A ton of energy, big plug gaps, and long spark "dwell". I carry two batteries though.

Big LOP fan. Balanced injectors. In part for fuel savings, in part because it actually runs smoother LOP, in part to avoid plug fouling, and in part because my belly stays cleaner!


Duane Zavadil
RV 6A
IO-320

Roger,
I'm building a -9 in Fountain Hills. Could I look at your plane one of these days?

John Ragozzino
602-826-0710

Walter teaches these principles at the Advanced Pilots Seminars. Been there, learned a TON of info. Mike S., do you like Bar-B-Que? They put the feed bag on at Ada hehe..

GAMI Man

Walter Atkinson works for/with GAMI. Here is an interesting article.

http://www.sx300group.org/engine_care.htm

But yet you do and no

R.P.Ping said:

Gosh, I almost really hate to get involved in these posts any more. Can?t we have differences in opinions without step by step rebuttals?

Click to expand...

AND YET you get involved and go blaa blaa blaa lol To answer your question, NO. I do agree lets fly it, try it.

If it does not work, as the one gent said, lean to rough and (slowly) push it in about 1/4 inch**. Imperfect mixture distribution is a challenge for LOP ops with Carbs. Clearly the heat/crack procedure is not suitable for a rental fleet, with renters in planes that have no or one EGT gauge. That I think is without dispute. In our experimental lets experiment. Why not. George

PS:
Dan, thanks for pointing out the other advantage, I appreciate you keeping me straight. I did not think of that. I see that. I know any engine leaned properly, even during taxi benefits from leaning. Engines run excessively rich have problems.

Yukon: Thanks, intereresting, I'll read it.

** Lycomings info on leaning http://www.lycoming.textron.com/mai...ons/keyReprints/operation/leaningEngines.html

Lycoming says........

Taken from Lycoming Leaning Instructions......

"When leaned, engine roughness is caused by misfiring due to a lean fuel-air mixture which will not support combustion. Roughness is eliminated by enriching slightly until the engine is smooth."

Several posts have explained the roughness as the imbalance of power pulses, ie the rich cylinders are producing more power than the lean ones
Lycoming seems to be saying here that the lean cylinders are not running at all......and interesting contradiction.

Lycoming's statement is misleading. An engine with poor mixture distribution will run rough due to the power imbalance between cylinders long before it actually reaches the point of lean misfire.

Walter,

I have a simple RV with O-320 F/P, CH temp for 4 cylinders & a single probe EGT. The engine runs smooth LOP. If I climb to cruise altitude & set power at 75% or less, what is the best way to lean this engine for cruise?

BOB

Walter: Thanks for bringing a little science to the party. Real data is rare and precious. Now a question: I recall, many years ago, that we were advised not to run LOP because the excess oxygen in the exhaust gasses created an oxidizing flame that would erode the valve stems/faces/seats and create $$$ trouble. The analogy was to welding with an oxy-acetylene torch and the necessity of avoiding the oxidizing condition (unless you were cutting metal). What happened while I slept? Do we no longer consider the excess oxygen in the exhaust gasses to be harmful? Just curious. I am looking forward to finishing my RV7A with a 180/carbureted Lyc and learning from the engine monitor, including running LOP if I can. Now, here is a little non-RV story that I offer apropos nothing at all. I used to own a Cessna 195 with a Shakey Jake 300hp carbureted normally aspirated engine. Absolutely wonderful old airplane, man I miss it terribly. Anyway, the word was, to expunge the shake from the Jake, just run about 80-100F carb temp and the shake would go away. It worked. Leaning was easy, too. Just watch the bolt on top of the cowling while slowly (no, slower than that) backing out the red knob. When the bolt began shaking almost imperceptibly, (1) stop right there, and (2) turn the red knob back in a wee bit. That was all there was to it. The engine ran as smooth as this frozen concoction I have here and no cylinder distress in many hundred hours. Was it peak, LOP, ROP? No EGT so I couldn't say. I lean my Lyc 0-290D in my PA-12 the same way, only I feel the shake in the rudder pedals and sweeten up the mixture to make the shake go away. Seems to work fine. So Walter, bring on the science, I want to learn more. Steve

Real Numbers

On my Saturday morning breakfast flight with the boys the destination airport was far enough away to allow for some high altitude experimentation with LOP operation. I had a passenger to record the data and I also took pictures of the EFIS. I forgot to take a picture of the initial set up so I will give you the data. You can see the data for the other two conditions.

Density altitude for all was 12,980ft. EGT and CHT are shown left to right as: front left, front right, rear left, rear right.

First set up is WOT leaned to the first cylinder to peak EGT.
MAP: 20.3?, FF: 7.3 gph, EGT: 1359, 1320, 1246, 1255

Second set up was throttle plate positioned ever so slightly to distribute air/fuel mixture more evenly to the cylinders. This brings 1 & 2 down and 3 & 4 up and alows for much more leaning before the first cylinder peaks. Here?s the number even though you can see them.
MAP: 20.2 FF: 6.5 gph, EGT: 1365, 1319, 1346, 1351

Third set up was the same as set up # 2 but LOP
MAP: 20.2, FF: 6.3 EGT: 1375, 1364, 1349, 1345. ( cyl 4 is 8d LOP, 1 & 2 are at peak & 3 is 12d ROP

Conclusion: Slight repositioning of the throttle plate to obtain the best fuel/air mixture to all cylinders allows for the most amount of leaning before the first cylinder peaks. The loss of 0.1 ? of MAP seems negligible compared to the much more even combustion in all cylinders. Running LOP from this point did offer a slight increase in efficiency.


Note: The difference in true airspeed from 158kts to 154kts may or may not be attributed to engine operation and could be attributed to piloting skills. (I?ll have to test some more on a cross country flight). Also, these are the readings taken at one specific point in time. The more time spent fine tuning and waiting for temps to stabilize can affect these numbers.

Yukon said:

Walter Atkinson works for/with GAMI. Here is an interesting article.

http://www.sx300group.org/engine_care.htm

Click to expand...

So what's your point here John?

Worried walter is here trying to make big bucks selling GAMI injectors to pilots with Carbs?

The thought maybe occur to you he is just pitching in with a wealth of info and experience about the subject at hand?

I don't think GAMIs sales are going to go thru the roof because he took the time to offer info to a group that has no use for GAMIs.

Milt:

A little house-keeping just attaching to your last post.

1) Lean misfire, in the context Lycoming is using does not exist. The roughness is as explained above--the Hp differences. We can prove this on the engine test stand and do, regularly to those who wish to watch it. The *misfiring* cylnders are still running--clearly.

TRUE Lean misfire is the same phenomenon as rich misfire. The F:A ratio is not appropriate to burn.

2) An exhaustive search of the literature concerning exhaust errosion from oxygen rich exhaust has revealed not one, single report of this being a probelm over the course of over 400 million hours of LOP operation. One would think that if it were a problem there would have been ONE case at least! There is no blow-torch effect. I liken this to the effect of standing in 1/4 inch of water or 3/8 inch of water. Neither are a threat to drowning!! I have a graph of the O2 contents of LOP and ROP exhausts. The difference is underwhelming.

The BIG exhaust issue is CO. There is no measurable CO in LOP exhaust. We all know that an exhaust leak can kill you when ROP.

Walter

Walter, I think that was you in Cessna (Spam-can) Association that talked about LOP Ops? We have a few carbed 182's here that operate successfully LOP with a full engine monitor. Using Trottle/Carb heat to balance everything out at 7,500 or higher cruse. We have one craft here that gets down to 9.5 GPH at low MP setting and likes the economy and cooler temps(even at lower altitudes)- For my old 182D though- The EGT's(the five that work) spread is so touchy- Only at one T/CH position where I can get the balance right- about a 45 deg spread. We where thinking a induction leak/old jugs/uncoordinated pilot were to blame-Whatever- The 182's are good family haulers, but I can't wait for the efficiency of my -6

Brad
RV-6A Firewall forward

Air Box Magic for LOP?

BOBM and R.P.Ping, that is good info. I am encouraged that you got LOP with carbs. BOBM you have a basic set up. I find it interesting you are doing LOP with one EGT. I guess if you are running smooth, under 70-75% power why not. How lean of peak are you running. Question to both? Are you using Carb heat?

AZtailwind said:

Walter, I think that was you in Cessna (Spam-can) Association that talked about LOP Ops?Brad RV-6A Firewall forward

Click to expand...

Brad now that you and Walter mention it, I recall the C182 trick. I was giving a biannual flight review to a guy in his own C182; he tried to show me the technique but could not get it right on that flight.

Comments about Carb Heat and Throttle manipulation has me thinking about Van's air box, which is way differnt than a C182 airbox (I recall).

LOP is about balancing the power or getting the EGT "peaks" to be closer together. So the throttle plate allows some "trim" between cylinders.

The Carb heat as Walter says aids in atomization. I think another reason Carb heat works on a C-182 to aid LOP operations, besides the heat itself (atomization), is the C-182 airbox/carb heat valve is near the throat of the Carb. That valve could contribute to redirecting the balance to the cylinders? This gives me an idea.

Carb heat on Van's air box is marginal. It's just a flap on the front of the box, well away from the Carb and outside the air filter. It really just shuts the outside off to the airbox and opens a very small restricted opening into the cowl area.

http://www.vansaircraft.com/cgi-bin...58-336-39&browse=engines&product=fab-vertical

The idea is a small "GUIDE" in the bottom of Van's airbox, right under the Carb throat**, so airflow can be redirected? The idea is to send a little more or less F:A down one of the four induction tubes.

** This location is where Van now has the optional ALT AIR door, that's cable operated. That alt air door could act to help balance the A:F distribution? Hey they don't call it experimental for nothing.

Cheers George

Basic Lop

"I find it interesting you are doing LOP with one EGT"

You don't need an EGT with a F/P prop, the prop works like a torque meter or BMEP gauge. Set the RPM 100 above what you plan to cruise at, then lean until RPM drops the desired amount & stop. The big drop in CHT on all 4 cylinders (& greatly reduced fuel burn when you fill up) confirms you have it.

Ignition's affect on LOP

While there has been mention of EI in this thread, I believe its affect on LOP is dramatic, whether carb or FI. I have about 750 hours of LOP operation, typically at 22", 2300, 7.1 to 7.3gph in my O360 with balanced (.2gph) Airflow Performance. All of these hours have been with a Lasar system providing the ignition. Typically, I would run at about 20 to 50F LOP with the above settings. Generally, I could not dial the fuel flow down below about 6.8 gph or so without some roughness (not that I necessarily wanted to for power loss' sake, but it does provide an interesting data point).

I recently replaced the Lasar system with dual Lightspeed ignition systems, and the ability to run LOP is dramatically different. While I only have one flight as of now, I was able to run smoothly down to 5.5 gph with the same MAP and RPM as above. I will get more data, obviously, but this result was startling. I was told to expect that, but I really didn't believe it would be that large of a change! There were other interesting, positive changes, but I need to get more flights and hours to confirm.

In the next couple months, I will post comparative data between the Lasar and the Lightspeed systems.