Just wondering about others experience with LOP operations on carburated engines? I've been operating LOP in cruise power settings @ 65% power or less above 3000' altitude/DA for the last 900 hours with no problems. On takeoff full rich or leaned for altitude/DA, and climb at 100+ ROP. Normally don't climb much, and after takeoff level off around 500' AGL and pull back to around 22"/2400RPM and lean to around 10.5 GPH. If climbing higher than 500-1000' AGL I stay ROP until cruise altitude.

The temperatures @ LOP are CHT's in the 285-360 range and EGT's in the 1300-1450 range. The fuel burn is around 10.5 gph at 65% power instead of around 12-13 gph ROP. The temps ROP at 65% and 75% power are CHT's 350-385, and EGT's 1250-1450. The difference in speed @ 65% is about 2-3 mph less at LOP vs. ROP. On real hot days like lately, it seems that 100' ROP or more is necessary to keep cylinders nice and cool, LOP provides much cooler CHT's on hot days. Cowl flap extenders also help alot!

IMO running LOP on a carburated engine at higher power settings than 65% and altitudes/DA's lower than 3000' is where most of the burning up valves and all the bad mouthing about LOP come from. What is your experience, for sure YMMV?

I know I am not the only one out there operating this way or wondering why so many are so against LOP operations??? Heat is the enemy of engines and my temps are way WAY better operating LOP. Fuel burn is significantly less, and lead fouling of plugs is much less.

-Skalywag

P.S. 900 hrs X 2 (gph) = 1800 gallons X $5 (per gallon) = $9,000!!!!!!!
My new engine is 2500 TBO if I run that way for 2000 hours that's 4000 gallons of fuel saved = 4000 X $5 = $20,000

This guy runs 100° rich of peak now. On my third exhaust and a $30,000 engine. I'm not even saying you shouldn't do what you are doing, I'm just saying what I do.

Cheers

I run the O-360 Lyc in my Husky LOP. In fact at around half power, 1950 rpm and 21" (my airport is 4750' and summer hot) the CHT's and EGT's are all straight line even on the engine monitor. This is not the case at full throttle, so I'm guessing the butterfly in the carb adds enough turbulence to help even out the fuel distribution. That power setting nets about 105 knots and burns 6 gph . The MT prop seems very efficient when turning slow.

Pouring the coals to it burns more than 10 gph and gets 117 knots at 7,000 feet with 26" tires - - hardly worth the added fuel cost.

bumper

As soon as one of my cylinders goes lean of peak, the engine runs too rough to continue leaning--that's at 21" and 2400 rpm. I have an Insight G-1. The cylinders all peak at different amounts of leaning. So I can't run LOP at all.

Cary

Cary, I flew an 0-470 once that did something similar to what you are describing. The temps were cool and stable ROP, although running richer than it should have to run smooth, like 150-200 ROP and 15-16gph at 75%. However, when attempting to run LOP it exhibited the same symptoms you describe, the engine would only go to peak on a couple cylinders and then run rough if leaned any further. So checked the timing and it was at 20 instead of 24. Re-set the timing and voila, ran great at LOP and ROP burning substantially less fuel ROP as well, 1-2gph less depending on power setting. Just an idea, 0-320 and 0-360's should run LOP like Bumper described.

I've just had my IA change the timing from 25 BTDC to 20 BTDC, because of an overheating problem with the back 2 cylinders--advice received from Mike Busch of EAA engine guru fame. The overheating problem was materially reduced by doing that--they still run warmer than the front ones, but not nearly as hot. But I couldn't do LOP before, and it reacts almost exactly the same now.

I'll be heading off to OSH at the end of the month, and whilst cruising along, I'll fiddle with it some more at different power settings and see what it'll do, but normally LOP ops aren't too successful with most carb'd engines due to uneven fuel distribution. With mine, the intake system is a modified Mooney system, as the conversion engine originally came from a Mooney. When it threw a rod through the top of the case some 8 1/2 years ago, the engine was completely redone, but the intake and exhaust and oil cooler were about all that was salvaged.

Cary

This guy runs 100° rich of peak now. On my third exhaust and a $30,000 engine. I'm not even saying you shouldn't do what you are doing, I'm just saying what I do.

Let's see $30,000 engine with fuel at $6.00/ gal. works out to 5,000 gallons of fuel.

How may GPH will LOP save you? You can do the calculations and see if the risk/reward ratio works out for you.

TD

Caveat - I'm replaying stuff I've read here, not stuff I've learned the hard way:

The modern thinking seems to be there's nothing but benefits for the engine running LOP - IF you know what you're doing. Mike Busch's seminars on "advanced leaning technique" can be watched online and tell you enough to understand basically what's happening to the engine as you work the controls. It sounds like you're doing all the right things and making all the right noises already.

The O-470 is supposed to be the hardest engine to run LOP because of the uneven nature of the fuel-air mix. They say cocking the throttle slightly will help.

I have tried running an IO-470 with GAMI injection LOP, never had any rough running or unusual temps etc. Seems to do nothing bad, just saves fuel.

LOP risk comes from running richer than 50 DEG. F and leaner than 100 deg. F. or more at high power settings,on any cylinder, it’s not the lean cylinder that burns up it’s the one 50-100 ROP making the highest power/heat, heat IS the enemy, the highest heat occurs at the highest power settings and 50 to 100deg F. ROP. CHT temps are the critical ones. Use an engine analyzer and chase away the boogey man, the engine analyzer tells you how far you can push it without damaging the engine, set your CHT alarms 30Deg. below max operating temp and keep your engine cool, the engine will last longer and cost less to operate. There is my two cents worth.

Cary wrote:As soon as one of my cylinders goes lean of peak, the engine runs too rough to continue leaning--that's at 21" and 2400 rpm. I have an Insight G-1. The cylinders all peak at different amounts of leaning. So I can't run LOP at all.

Cary

Have you tried Bumper’s power settings?

Oh yeah, the other thing to think about is manufacturer's max CHT limits are ridiculously high for continuious operations. Subtract 50*F and then set you mental (or instrumented) alarm level another 30*F lower again if you want to be extra safe when LOP in cruise. So in a Lyc -540, manufacturer's 450*F max CHT becomes 370*F alarm level - the point you take action to cool it down.... lean/enrich away from peak, open cowl flaps, increaase airspeed, reduce power). That may not be possible in climb which is why nobody tends to climb LOP...

Remember that damage can be done really fast at high power settings with a lean mixture and/or lower RPM, and the CHT has a slow response time compared to when the damage starts.

Have you tried Bumper’s power settings?

No, I rarely have run less than 2200 rpm except in the pattern as I'm coming in to land. As I said, I'll do some experimenting on the way to OSH--it's 8 hours of flying anyway, so a few minutes longer won't make much difference, and it'll give me something to do across Nebraska!

Cary

If you are having trouble running LOP with a Carb... try a little Carb Heat and see if that helps (it does in big radials).

By the way, its not running Lean that damages the engine.... its not running rich enough.... someone said it already- Heat is the enemy. You want to stay out of the zone 30 deg LOP to 100 deg ROP. The heat is the result of high Internal Cylinder Pressures... stay away from peak EGT and you'll be fine. I do not suggest you try this without an Engine Monitor.

gunny

Watch your descents too. Supercooling the engine will kill it just as fast as hot cruise temps.

Thanks for the input guys, this is a subject that I just can't seem to beat up enough. Realized very early on that about everyone I talked to had a different opinion on how a carburated aircraft engine should be operated. Actually kind of drove me nuts in the beginning, having that much invested in an aircraft I couldn't stand the thought that I might be screwing up the engine.

Gunny, I wonder why carb heat helps the big radials run LOP better, interesting? That brings up another benefit of LOP, much less risk of carb ice.

This is the first I have heard of the range of less than 100 ROP and more than 30 LOP. Makes alot of sense and seems very straightforward.

I know a guy who has flown a crazy amount of different aircraft over a 40+ year career. This guy runs 50 ROP for "best power" and runs hard, took many a motor past TBO and without any fancy gauges this way. If we were still in the days of $1 per gallon avgas and $20,000 cherry 180's I would probly run hard at best power too, while chewin a cigar and flying like I stole it

Found this excerpt from Texas Skyways to be interesting, this is directly from Texas Skyways website and is Jack's directions on how to run your TS motor. Does not say it here but he told me never run LOP, but its ok to run at peak while at lower power settings.

Quoted from Texas Skyways:
Leaning Procedure: A good rule of thumb, "lean it until it gets rough, then richen it until it gets smooth, then just a little bit more". If you do this at 8500', full throttle, 2400 RPM, the engine will be using about 14 GPH. I won't argue with 13-15. Most 520 and 550 engines will be in this area of fuel burn.

Most of us have heard that we should run the EGT 100° Rich of Peak. That is true in some instances, but not all. If you are operating the engine at low power settings, as in high altitude, and peak EGT is only 1200°F, you would then be operating at 1100°F EGT.

It is not "Peak" that burns up a cylinder. It is "High Temperature". The manufacturer says to not exceed 1600°F EGT. We have set the carburetor very rich and probably you can't get to 1600°.

If you have a six probe EGT system, lean the engine and watch for the EGT's to stop increasing and start to decrease. You have found "Peak". If peak is only 1400°F, you probably should stay there. Remember1600 is maximum. Normally the engine should be operated at 1475°F or below. At higher altitude, the temperature will not be that high. Run closer to peak or at peak.

Descending: When descending for prolonged periods of time, keep the engine pulling by decreasing RPM. Reduce throttle to control speed, richen the mixture to maintain proper EGT. Close the cowl flaps to maintain proper CHT and oil temp. Do not fail to richen the mixture. With the reduced throttle setting and increased air to the engine at lower altitude, the engine may stop running. Richen the mixture for restart."

-Ok enough BS, goin flyin its 72 deg in July what a day!!!

Gunny wrote:If you are having trouble running LOP with a Carb... try a little Carb Heat and see if that helps (it does in big radials).

By the way, its not running Lean that damages the engine.... its not running rich enough.... someone said it already- Heat is the enemy. You want to stay out of the zone 30 deg LOP to 100 deg ROP. The heat is the result of high Internal Cylinder Pressures... stay away from peak EGT and you'll be fine. I do not suggest you try this without an Engine Monitor.

gunny

And, the blue ribbon goes to Gunny

The key to running carbureted engines lean of peak is use of partial or full carb heat. I personally will never run any engine lean of peak unless it's equipped with an engine monitoring system.

My #2 cylinder runs waaaaay hotter than the other three, but when I apply partial carb heat in flight, those bars on the EDM 700 smooth out pretty as you please. Looks like a fuel injected engine. THEN, lean it to the peak side.

Is there any harm to running carb heat in flight? Not really. Unfiltered air of course, but there really shouldn't be much particulate up there in any case, unless you're operating downstream from an erupting volcano. In that event.....run ROP.

MTV

I will add the carb heat into "the mixture" My Insight analyzer has a carb temp readout, too, so all this will be interesting.

Cary

If memory serves then some of that stuff from the Skyways site is baloney. I dont think EGT matters a hoot in terms of directly damaging the engine because of the hot combustion - provided the cylinders themselves dont actually overheat. I think the EGT is really just a proxy for the stiochometry of the combustion event. The combustion temp inside the cylinder goes WAY in excess of measured EGT prior to the gases being exhausted.

Skalywag-

Carb heat adds a little swirl and improves the fuel-air mixture in the intake system (if you can envision a 'lumpy' mix normally.... it is not very uniform in any intake system).

For Fuel Injected engines the nozzle injects the fuel directly into the cylinder and GAMI in Ada, OK has perfected those nozzles, adjusting the flow through each nozzle for each Cylinder in the engine (each cylinder requires a different amount of fuel to have an even fuel-air mix). George Braly, GAMI chief engineer and a really smart guy, has led the LOP charge for years. GAMI has a test stand to develop actual data about how an engine operates... they have thousands of hours of test data and that Red Box area 30deg LOP to 100Deg ROP is from their data. 50deg ROP is where 'Best Power' is... for sure... but not the best place to operate your engine... emphasis 'your'.... if you pay the bills stay out of the Red Box. An Engine Monitor is worth its weight in gold.... number 1 upgrade recommendation.

There is a caveat.... in a normally aspirated engine power will drop off with altitude and you can run your engine at Peak EGT all day long if you are below 65% power. LOP will save you gas, it won't give you speed. This LOP discussion started heavily in the mid-90's and in the Fuel Injected GA world these days LOP is largely accepted. It received vehement opposition from believers in old wives tales.... real data cuts the BS.

The LOP/ROP issue is a personal choice... you spend the money, you make the choice. But real DATA, from running engines (as opposed to anecdotal 'data') shows that if you run ROP you should be better than 100 deg ROP to avoid that red box... where you will burn valves. LOP doesn't kill engines... running ROP, but not rich enough does. I could go in to a discussion as to the why's and whats really happening... but thats a better discussion for chairs at the hangar in the shade rather than this over long post.

My two cents,
gunny

Battson wrote:If memory serves then some of that stuff from the Skyways site is baloney. I dont think EGT matters a hoot in terms of directly damaging the engine because of the hot combustion - provided the cylinders themselves dont actually overheat. I think the EGT is really just a proxy for the stiochometry of the combustion event. The combustion temp inside the cylinder goes WAY in excess of measured EGT prior to the gases being exhausted.

Battson pretty well said... I love that word Stoichiometric..... but the key issue in the cylinder is not the combustion temp (the temperature of combustion is nearly constant, the speed of the flame front is a function of the fuel-air mix ) it is the Internal Cylinder Pressure as a result of the combustion event. The speed of the flame front impacts when the cylinder reaches peak pressure.... and where that occurs during the piston compression cycle. What you don't want is for the peak compression to occur in conjunction as the flame front progression. If that happens the peak pressure can be WAY higher than the cylinder can handle. Peak power occurs at a 'perfectly' balanced fuel-air mix.

There is some BS and a large amount of vagueness there in that quote. EGT is an indicator of what is going on in the engine... a trend indicator, pay attention to it, but it is not controlling.... CHT is controlling. The EGT numbers cited pertain to the ductility of the exhaust metal..... stay below 1600 deg to avoid trashing your exhaust is a good observation. I actually use a lower number myself.

The interesting thing about the leaning advice (lean it until it stumbles and then enrichen just a little---- what I was taught when I first learned to fly as well).... if you have an engine monitor this profile usually results in LOP operations.... from my observations for a smooth engine (with a little carb heat) it results in about 100deg LOP.

Your milage may vary.

gunny