Hg"/Prop RPM ?Curious

[BudG]

I'm new at flying a fuel injected IO-54O W1A5D and a Maule. I've got about 80hrs on my M-5 now and just added a JPM-EDM-700 and GAMI injectors and vortex gens with 6.5X6.0 tires. I have been cruising at about 21-22"MP and @2150-2250RPM showing 135mph-140mph air speed at 11-11.5Gal fuel flow at about 8000ft.. My question pertains to the Is this the optimum cruise setup. I can dial it back to 120mph at 21square and get 9.5-10 gal/hr. at 8000ft at 20-25deg.lean of Peak. Am I setting it up properly for faster cruise? I have been playing around with it don't seem to get more than 135-140mph even with the higher fuel flow. I read the stats on an M-5 and understood that the Lunar Rocket got 150mph cruise. Even before the vortex gens I was getting about the same mph.Anyone with thoughts on that and takeoff power settings of 29"hgMP and 2450RPM. I was tought that one doesnt want to run too much MP over RPM.
Tailwinds 2U
BudG

[maules.com]

If your outside air temp at 8000msl is 31deg F which is standard, and the barometer 29.92, then 135- 140mph indicated is 156-162mph TAS and 11.5gph is excellent. You would expect an EGT spread of about 70deg before Gami modification.
Given a no wind situation (never happens) your mpg is 13.5-14 at the faster speed and 13.9-14.6 at the lower speed and as drag increases with speed, you would expect less mpg at higher power settings.
The best mpg will usually be achieved at a 55% power setting taken from your Lyc operaters manual graphs.

[a64pilot]

You can run a Lyc seriously "oversquare" without hurting it. Check your engine manual. You will see a small increase in fuel mileage at lower RPM and higher manifold press due to slightly less friction losses in the engine and slightly less drag on the prop. I run either 2200 or 2300 on mine. It's smoothest at 2300. At above 7000 or so I'm firewalled and usually 2300 if I'm travelling.
Above 5000 or so I don't think you can "oversquare" it by much, you just can't get enough manifold pressure.
Of course don't do anything not approved in the manual, like running LOP
If your getting 140 kts true, then your around 5 kts. faster than my old M-6 and I think from what I've seen about 10 kts. faster than a new Maule. Not bad for an old airplane is it?

[BudG]

Thanks for the info! The egt/cht's when running lean of peak with the new Gami's are about 20-30deg. cooler and my cylinder heat temps are down from 370deg @ to the 340 range and oil is 178-181deg. The Gami web site has some really interesting information on running an engine lean of peak with the proper injectors. Once again Thanks. I guess when I was using my whiz wheel for the TAS I left something out.
TAILWINDS 2U
BUDG

[maules.com]

BudG, I'm wondering what your EGT spread is between all 6 cylinders when l.o.p. and when 25 r.o.p. ?
Which cylinder is proving the hottest?

[BudG]

In cruise it seems to be about 50deg spread on the egt and about 20 on the cht. #3 seems to be the cylinder that the JPI finds to be the leanest and I dial it according to that cylinder. I can't remember which cylinder is hottest at r.o.p. I'll have to go fly and do the rich of peak. I'll be honest. Since its a new piece of equipment I haven't gotten precise on the rop yet but I will check it out. I ran it at 11.5 g/hr then just richen it until I see the drop on the JPI then lean it to the highest temp, push the Lean Find button and it searches for the leanest cylinder, #3 then I just dial it down to about 30-50deg on that cylinder. My baffling is a little old so I'm going to replace that, and there is a cooling duct on my plenium that goes nowwhere and it could be plugged. Just so happens that it is adjacent to the #3 cylinder???which might be the reason for the temp spread on that cylinder. I'll keep you informed and thanks for your time.
Bud
Tailwinds2U

[a64pilot]

When running LOP, you want to be X number of degrees of the richest cylinder, not leanest. When ROP, you want to be X number of degrees from the leanest cyl. Lycoming is very much against LOP. I have had the Gami's and an analyzer on both the aircraft I usually fly. The Cessna with the Conti loves LOP, but my Lyc even though it runs smooth LOP, it loses so much power it doesn't seem worth it, that along with Lyc being so much against it, keeps me ROP. Specifically the part that I worry about LOP is the valves, especially the exh. Time will tell, I guess.
Lyc. suggests running at peak for economy cruise, something I just can't understand either, but suggests ROP for greater engine longevity.

[Maule 9V]

When leaning with a JPI-700, the last cylinder to peak is the one referenced when going LOP, and the first to peak is referenced when going ROP. When lean of peak, the difference in fuel flow (if fuel flow is installed) between the first and last cylinders to peak is a measure of how evenly matched the fuel flow are between all the injectors. This is assuming the engine has GAMIs.

[maules.com]

I would agree with A64, I have found that LOP on the Lyc produces such a power/thus/speed loss that little if anything is gained. You will find me at ROP or at low power settings, i.e. higher altitudes close to but still ROP and I've never failed a valve or cylinder in 33years.

[BudG]

Thank you all, for the experienced touch to this confusing matter. I was wondering, If the cylinder head temperature is running cooler at LOP how is a valve going to get burned? I would think that it has more of a chance of fouling from not being hot enough. Is it because of the reduced amount of lead that lubricates the valve?
BudG
Tailwinds2U

[maules.com]

The more likely problem running LOP is detonation damage as the flame front changes which is equivalent to timing advance.
Lead nodule fouling from too cool a burn will become hotspots and cause pre-ignition, which is damaging but not as dramatic as detonation, which can destroy an engine very quickly, starting with the pistons and then the babbit shells.
The difficulty with an aircraft engine is that you cannot normally hear the detonation death rattle taking place.

[a64pilot]

Thank you all, for the experienced touch to this confusing matter. I was wondering, If the cylinder head temperature is running cooler at LOP how is a valve going to get burned? I would think that it has more of a chance of fouling from not being hot enough. Is it because of the reduced amount of lead that lubricates the valve?
BudG
Tailwinds2U

The cyl head temp is I believe directly porportional to the power out put more than egt's. The power output of an engine is much lower 25 degrees LOP than it is say 50 deg ROP. Max power I think is around 100 ROP or so. Any way I fear the exhaust valve because usually the EGT is higher LOP, and it's EGT that the exhaust valve "sees". It would be highest at peak, which Lycoming recommends for economy cruise. That is what confuses me. If peak isn't bad, then why is LOP?
If you have an accurate fuel flow that will read in decimals try running at several power settings and LOP and ROP and recording both the fuel flow and GPS ground speeds so you can compute MPG. My tests initally showed about 20% decrease in fuel consumption between ROP and LOP. I was happy, it justified the Gami's, but when I reduced the power when I was ROP to obtain the same speed as when I was LOP most all of the fuel savings evaporated. It was apparently the lower speed that LOP produced that was the majority of the fuel savings. The difference between fuel consumption LOP and ROP, or for that matter at the Lycoming recommended peak is negligable if you eliminate the variable of speed. So I came around full circle and now at power settings less than 75%, I run 50 deg. ROP again.

[Walter Atkinson]

Gentlemen:

Some thoughts on this discussion:

**In cruise it seems to be about 50deg spread on the egt and about 20 on the cht. **

EGT spread is meaningless. What's important is that they all reach peak EGT at the same FF. That means they are balanced. The raw EGT values are pretty meaningless. The CHT's being close is meaningful in that you can be assured that if the FF balance is correct that the baffles are good and the cooling is balanced.


**my Lyc even though it runs smooth LOP, it loses so much power it doesn't seem worth it, that along with Lyc being so much against it, keeps me ROP. **

1) that is a strong indication that you are not operating optimally LOP. The difference between best power and optimal LOP mixture in most cruise configurations at altitude is 3 knots but 2.5-3 gph fuel savings. I've demonstrated that in many, many different aircraft--which only serve to confirm the laws of physics!

2) Lycoming's position is curious. It does not agree with their OWN data. Even in their "Experts are Everywhere" document, they say that LOP is OK, it works and is in harmony with the laws of physics but that YOU, the PILOTS are too stupid to do it right. That's encouraging. I disagree with that view.

**Specifically the part that I worry about LOP is the valves, especially the exh. Time will tell, I guess. **

No, time will not tell. The DATA will tell. The mixture that results in the hottest exhaust valve temperatures is 25dF ROP.... right where many OEMs recommend that we run the mixture. Go figure?

**Lyc. suggests running at peak for economy cruise, something I just can't understand either**

It makes sense once you realize that Lycoming's engines as delivered have such poor F:A ratio balance that they will not run smoothly LOP. Who wants their customer service lines ringing off the hook? <g>

**You will find me at ROP or at low power settings, i.e. higher altitudes close to but still ROP and I've never failed a valve or cylinder in 33years.**

When you are low power settings, you can run the mixture anywhere and not hurt the engine. Your engine will prefer being 10dF LOP, though, as it will run MUCH cleaner. Plugs, rings and the oil will all stay a lot cleaner. That's better.

** the reduced amount of lead that lubricates the valve? **

Lead as it exists during the combustion event is a salt of bromide. Salts are abrasives. Abrasives make crummy lubricants. Lead is NOT in the fuel to lubricate ANYTHING. The purpose of the lead is for ONE reason ONLY. It widens the detonation margin. Period.

**The more likely problem running LOP is detonation damage as the flame front changes which is equivalent to timing advance.**

No. The detonation margin is MUCH wider when LOP. It is virtually impossible to initiate detonation LOP--the folks at the Carl Goulet Engine Memorial Engine Test Facility have tried and failed miserably. The MOST detonation-prone mixture setting is 40dF ROP--according to all known scieintific sources and the physics.

**Lead nodule fouling from too cool a burn will become hotspots and cause pre-ignition, which is damaging but not as dramatic as detonation, which can destroy an engine very quickly, starting with the pistons and then the babbit shells. **

Whoa! There is no known reference for that.

1) The combustion temperature is between 3500 and 4000 degrees F. Any notion that 3500 degrees is cool is curious.

2) Pre-ignition is most frequently caused by a bad spark plug, secondarily by a helicoil tang and rarely by anything else, although a piece of glowing carbon is blamed often, there is no data to suggest that that happens. Lead is NOT the cause because it MELTS at a temperature low enough to not glow red!!!!

3) Pre-ignition is VERY destructive. Although detonation is often blamed as being destructive, it really is far less so. We have run an engine under 20 hours of light detonation; 3-4 hours of medium detonation; and 30 minutes of heavy detonation and afetr tear-down by an independent expert was pronounced as normal in appearance with no visible damage whatsoever.

**The difficulty with an aircraft engine is that you cannot normally hear the detonation death rattle taking place.**

That is true.

**The cyl head temp is I believe directly porportional to the power out put more than egt's.**

CHT is a result of heat IN and heat OUT. It gets waaay to complicated to discuss in this thread.

**The power output of an engine is much lower 25 degrees LOP than it is say 50 deg ROP. **

Not so--necessarily. You can produce more power at 25dF LOP than at 50dF ROP, but the MP and RPM will be different.

** Any way I fear the exhaust valve because usually the EGT is higher LOP, and it's EGT that the exhaust valve "sees". It would be highest at peak, which Lycoming recommends for economy cruise. That is what confuses me. If peak isn't bad, then why is LOP? **

LOL! Yep.

EGT is NOT what affects exhaust valve temp. As the EGT rises from 25dF ROP to peak EGT, the exhaust valve gets cooler.

One should remember that 25dF ROP is the EXACT same temperature as 25dF LOP!

**If you have an accurate fuel flow that will read in decimals try running at several power settings and LOP and ROP and recording both the fuel flow and GPS ground speeds so you can compute MPG. My tests initally showed about 20% decrease in fuel consumption between ROP and LOP. I was happy, it justified the Gami's, but when I reduced the power when I was ROP to obtain the same speed as when I was LOP most all of the fuel savings evaporated. It was apparently the lower speed that LOP produced that was the majority of the fuel savings. The difference between fuel consumption LOP and ROP, or for that matter at the Lycoming recommended peak is negligable if you eliminate the variable of speed. So I came around full circle and now at power settings less than 75%, I run 50 deg. ROP again.**

Your test was flawed.

You can run at EXACTLY the SAME power setting ROP and LOP and the airspeed WILL be identical--but the FF will be MUCH lower LOP.

(consider the TNIO-550 in a TN Bonanza) If I produce 75% power (225HP) ROP at 18 gph, I will be going exactly the same speed as 75% power (225HP) LOP on 15 gph.

There's a lot of confusion about some of these issues being discussed here. The above notes are a few places to start the process of wading through them.

[John-Paul at GAMI]

Hello all,

Please let me introduce myself. My name is John-Paul Townsend and I work for General Aviation Modifications, Inc. better known as GAMI. I have been here 12 years, am a student pilot, and have a bachelors degree in Physics. My primary job functions are data analysis, product support, and sales. I sell GAMIjectors, but I'm not on this forum to push my wares. GAMIjectors basically sell themselves, I just write down the credit card numbers.

I received a call yesterday from a concerned Maule owner who believed there were some heavy Old Wives Tales (OWTs) circulating on around this post and asked if I could help dispel some of those misconceptions.

I received my account activation this morning and found that Walter Atkinson has already addressed most of those issues. Many thanks!

For those unfamiliar with Walter, he and a few friends put on a most excellent seminar about twice a year in person and year-round on the internet called the Advanced Pilot Seminars (www.advancedpilot.com). It is the ONLY seminar of its kind that teaches by SHOWING YOU THE DATA.

Having said that, I get NOT A PENNY from APS. I want to only illustrate that Walter has authoritative data on the subject.

Walter mentioned the Carl Goulet Memorial engine test facility. That is a fixture at GAMI. It is most likely the most technologically advanced aircraft piston engine test facility in the world. And though it is named after the former VP of Engineering at Continental, the most time has been logged on turbocharged Lycoming engines, notably the TIO-540-J2BD from a Piper Navajo Chieftain. We have literally spent hundreds of thousands of dollars (if not a million or more) researching and verifying the DATA in the TCM and Lycoming engine manuals as well as those from Curtis-Wright and NACA. Not surprisingly, between those entities the data is essentially identical. Funny thing about physics . . . it's the same worldwide.

We probably will never make a dollar on that research, but that was never the idea. The idea was to help the aviation community understand piston engine operation from a physical standpoint and leave OWTs behind. To do that we need to KNOW that when we say "This is how it is" that we can PROVE IT. We've made a lot of progress, but there are miles to go yet.

Textron Lycoming is one of the few remaining strongholds of misinformation existing for airplane owners. Frankly, they have their heads buried in the sand. Like Walter said, their own data conflicts with their recommendations. They are not yet willing to look at the data and be intellectually honest with themselves about the physics of the matter, however their are factions within that are trying to change that as company policy. We've seen a lot of that in the past at TCM as well as most of the major engine shops in the country. There are people within the company who know the score, but changing a COMPANY MINDSET is something that takes a lot of work from the top down and back up again.
Most of them have come around, but they have to be willing to look at the data. There are a few still remaining that say "We know what we know, and we don't want to know otherwise." That is not being intellectually honest with themselves or their customers. Walter has gone so far as to offer some of these folks free admission to the Advanced Pilot Seminar. They politely said "Not interested, thanks."

[flyer]

I have a question about this information. Do all of the tests and results apply also to those of us who use auto fuel? Do auto fuel mixtures work exactly the same when LOP or ROP? I assume that the laws of physics also apply to auto fuel.

flyer