[Frank N821BF]

I have a O-320, D3G in a 9A with dual Light speed ign and a GRT EIS with 4 EGTand 4 CHT. I have been running ROP. Can I safely run LOP or at peak EGT.
Frank

 

[aadamson]

Lop

Funny you should ask as I just posted an information message in the RV10 Speeds thread.

It's harder with a carb'd engine, but it can be done. If you also have fuel flow (and I think you do with the GRT), go to www.gami.com and read the "lean test" section.

Go try it and see what your results are. Most who fly LOP in a Carb'd engine have to use lots of carb heat to get the engine to run LOP.

If you are below 65% power, you should cause no harm.... But please don't take any ones word for it, go read up on LOP (avweb has lots of info), read all the deakin articles (also on gami.com) and learn how to do it.... As a reference point, go get the free "leaning guide" or whatever they call it at www.buy-ei.com and study that.

Good luck and let us know what you find. Those that use it, love it and it's much better for your engine if used correctly.

 

[Kyle Boatright]

Why would running carb heat make an engine run better LOP?

It may richen the mixture because there is less air in the mix at a given throttle and mixture lever setting, but I can't imagine why an engine would run better at, say a 1:14 fuel:air ratio when the air is warm vs when the air is at ambient temp.

 

[aadamson]

I honestly don't know, but it seems to work

I've only messed with LOP in an FI engine, but those that have tried it in a Carb'd engine claim that they can get it to work, if they use "judicious amounts of carb heat".

YMMV

 

[Captain Avgas]

Lean of Peak operations and GRT EIS

Why would running carb heat make an engine run better LOP?

It may richen the mixture because there is less air in the mix at a given throttle and mixture lever setting, but I can't imagine why an engine would run better at, say a 1:14 fuel:air ratio when the air is warm vs when the air is at ambient temp.

It might be because at the higher induction temperature the fuel is more evenly atomised in the intake air and thus more evenly distributed to the cylinders. This would reduce the fuel flow range between the first and last cylinders to reach peak EGT which is desirable.

Personally I don't like the idea of burbling around with degrees of carby heat on...other problems there.

I've heard of people running LOP with carbies but I think it must be nigh on impossible to achieve. Even with fuel injection the injectors need to be very well balanced for LOP.

Incidentally on another Forum recently some-one suggested that the GRT EIS leaning fuctions were only good for leaning Rich of Peak and not satisfactory for Lean of Peak operations. Considering that GRT claims on their website to have "Comprehensive leaning functions - the best at any price" I find this amazing. Is it true. Are the GRT EIS leaning functions not entirely adequate for LOP operations.

 

[dan]

Why would running carb heat make an engine run better LOP?

Here's what I read on the topic of LOP with carbs:

Carbureted engines and lean-of-peak mixtures

Many pilots assume that any engine-operating message coming out of Ada contains little information for pilots flying behind carbureted engines. Attendees at APS learn that the OWT that lean-of-peak mixture settings are the exclusive province of fuel-injected engines has also been popped. Because of uneven fuel distribution to the cylinders caused by rudimentary induction systems, carbureted engines usually won't run smoothly when the mixture is pulled past the peak EGT into the LOP range. Although this practice doesn't work on all carbureted engines, many pilots flying carburetor-equipped aircraft can take advantage of the benefits of LOP mixtures by adding partial carburetor heat during cruise flight.

Heating the fuel-air mixture in this way increases the molecular activity, resulting in a more evenly mixed and distributed fuel-air mixture. Atkinson flies a Beech 18 equipped with two carbureted Pratt & Whitney 450-horsepower R-985 engines. He has been successfully running his 985s LOP because of this carburetor-heat hint. Heating the inlet air causes a small drop-off in power, but the benefits of being able to run a carbureted engine lean of peak more than offset the loss of power. Benefits include reduced fuel consumption; an engine that's cleaner internally because of markedly fewer deposits on the valves, spark plugs, and combustion chambers; and drastically reduced levels of carbon monoxide in the exhaust gases.

Now, whether this practice translates to your O-320, ya got me!

 

[penguin]

My experience is that EI (e-mag in my case) makes running LOP much easier. It was not really possible with mags but now I can do it reliably. The problem is the split in the peaks due to poor fuel distribution (not much you can do about it with a carb). You will not have a problem at any mixture setting as long as you are below 65%, or maybe 75%. At higher power sttings don't run at peak EGT. If you can't get all the cylinders to run lop (and wot-lop is best) then you will have to run rop - otherwise you are in danger of detonation - look for rapidly increasing CHTs and decresing EGTs - if you see that throttle back or richen the mixture immediately. I have never experienced it, although I kept a good eye on the temps the first few times I ran lop.

With a standard carb heater (feeding directly into the bottom of the carb), the theory is that it channges the induction airflow engough to equal out the fuel distribution somewhat, making lop running easier. The Van's airboxes don't work like that, I have found no difference in using carb heat lop, so run cold air all the time.

The articles Alan quoted are an excellent source and a great place to start reading.

Pete

PS I use a GRT EIS-4000 and use the EGT page to get lop, once you are past peak it shows how many degrees cool of peak you are on each cylinder.

 

[aadamson]

Curious

My experience is that EI (e-mag in my case) makes running LOP much easier. It was not really possible with mags but now I can do it reliably. The problem is the split in the peaks due to poor fuel distribution (not much you can do about it with a carb). You will not have a problem at any mixture setting as long as you are below 65%, or maybe 75%. At higher power sttings don't run at peak EGT. If you can't get all the cylinders to run lop (and wot-lop is best) then you will have to run rop - otherwise you are in danger of detonation - look for rapidly increasing CHTs and decresing EGTs - if you see that throttle back or richen the mixture immediately. I have never experienced it, although I kept a good eye on the temps the first few times I ran lop.

With a standard carb heater (feeding directly into the bottom of the carb), the theory is that it channges the induction airflow engough to equal out the fuel distribution somewhat, making lop running easier. The Van's airboxes don't work like that, I have found no difference in using carb heat lop, so run cold air all the time.

The articles Alan quoted are an excellent source and a great place to start reading.

Pete

Hey Pete, got a question... I read on here sometime in the last 30-60 days that perhaps Carb heat on the RV's doesn't really work. I don't know all the details but it seemed that perhaps carb heat was actually acting more like bypass than actually creating heated intake. Could that be why it shows not difference?

 

[Ironflight]

Incidentally on another Forum recently some-one suggested that the GRT EIS leaning fuctions were only good for leaning Rich of Peak and not satisfactory for Lean of Peak operations. Considering that GRT claims on their website to have "Comprehensive leaning functions - the best at any price" I find this amazing. Is it true. Are the GRT EIS leaning functions not entirely adequate for LOP operations.

With my GRT EFIS/EIS, the systems page seems more than adequate for leaning, either ROP or LOP. The neat part is the real-time graph of all four EGT's, so you can see all of the cylinders, and where they are peaking. The digitals are equally easy, with the deltas from peak (for each cylinder) being displayed. You can go ROP or LOP - becaue the graph shows you the peak. I have to admit, although I've owned and operated aircraft for decades, I've usually been a "lean to roughness, then push in two clicks" kind of guy, because I never had instrumentation like this before. It all seems very intuitive to me. YMMV, but I'd urge folks to try it before they put too much stock into "I heard from a friend's brother-in-law's second cousin that..." kind of stories.

 

[aadamson]

Very good info

PS I use a GRT EIS-4000 and use the EGT page to get lop, once you are past peak it shows how many degrees cool of peak you are on each cylinder.

That's good info. Also remember if not sure about your engine monitor...be careful. You don't want to go 50 dLOP based upon the first cylinder to peak, you want to do it based upon the LAST. The former will have you running part LOP and part ROP - not a good solution.

I know that EI monitors and JPI monitors provide LOP specific features. For the others I have no idea, but make sure you understand your instrument before you wander off into this territory. While it a great place to go, education is KING about it.

 

[penguin]

That's good info. Also remember if not sure about your engine monitor...be careful. You don't want to go 50 dLOP based upon the first cylinder to peak, you want to do it based upon the LAST. The former will have you running part LOP and part ROP - not a good solution.

I know that EI monitors and JPI monitors provide LOP specific features. For the others I have no idea, but make sure you understand your instrument before you wander off into this territory. While it a great place to go, education is KING about it.

Absolutely agree, my leanest clyinder is usually 40 or 50 F cooler than the richest. I usually get the hottest around 20F lean at 8000'ish. Which cylinder depends on throttle setting. The EI allows me to run smoothly quite far past peak - could never do that with mags.

The carb heat on an RV heats the air going into the filter, so does not act like most certified systems that provide unfiltered hot air directly to the carb throat via a flapper valve at the base of the carb. We're not comparing apples to apples tho'!

Pete