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Lean of Peak Operation

rv6ejguy

Well Known Member
I'll start this out with a good video link on the subject: https://www.youtube.com/watch?v=h3bATVXMHQg

Our own testing on Les Kearney's RV-10 show similar gains in fuel economy as demonstrated here- about 8-10% at the same speed.

Background info on LOP:

Basic idea developed in WW2 to extend range.

Extensively used on radial powered airliners in the '50s and '60s, especially on the R3350 turbo compound engines. Was found to extend life of these engines which was a big deal. Proven in millions of flight hours here.

Approved by Continental and Cirrus.

Lots of good flight and dyno data supporting its use by the folks at GAMI, Mike Busch etc.

Still not accepted by many pilots and overhaul shops.

Let the discussion begin...
 
Seems engine longevity and overall reliability is driven by cylinder head temps. Running lean of peak reduces cylinder temps to levels that are very healthy for these engines. Reduced fuel consumption is a nice byproduct. :)
 
LOP

What's not to like?
-Less combustion deposits
-Lower Cyl Head Temps
-Lower EGT Temps
-Lower BMEP
-Less fuel burned
-Happier Pilot
-Happier Significant other

The only downside is that one has to have a well-balanced induction system that allows close EGT correlation between cylinders to prevent rough running.
Ed
 
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For me and my RV7A IO370 (9.6 CR) I generally cruise about 50 ROP (1350 ish EGT) with a small MPG penalty (maybe 2) but about 10 knots faster than 50 LOP. Never had a problem with CHT's so that's not an issue for me.

I'm running standard Bendix mags and even though my gami spread is around .2gph I still get a slight bit of roughness when LOP so I prefer smoother and faster.

I know LOP ops would improve if I installed EI and advanced the timing, but for me, the $$ spent on EI don't give me enough ROI, plus if something goes wrong away from home it can be much harder to resolve in the field.

Just for ref I've had every type of EI made on my old std 180hp engine (except for Surefly and CPI) so it's not like I am new to this.
I'm happy to take the approx 1gph penalty to go faster, run smoother, simplify system, no BU bat needed, etc..

I know, step in the future of aviation Walt!
 
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I started with two stoke air cooled motorcycle engines and spent a lot of time with port modifications and racing.
Getting into the Lycoming world and then the RV's I had a very hard time going lean. Death to a two stroke.
After a lot of reading I decided it made the most sense. I have been flying LOP since completion of my RV-9 in 2013.
I really think it makes the most sense. I really like the thought of less deposits and cooler running.
Oh and IO-320 and P-mags so I loose about 10 knots and drop from 9 gph to about 6.5 gph.
 
"Reference EGT" leaning at WOT for climb.

Peak EGT for fast cruise at altitude (ballpark 183 KTAS on 9 @2400). No worries about LOP, but it's not quite as smooth and it is way too slow.

50 or more LOP for goofing around, low power, low altitude, Sunday evening type stuff.
 
I now have several long cross countries on the new RV-8. Doing data runs as part of Phase 1 I found the plane has a sweet spot at 13K’ - 14k’. I run LOP exclusively.

At this altitude, I found WOT, 2490 or so RPM and just LOP, (~10 degrees), provides the best MPG. Engine injectors are balanced to 0.1 GPH. Dual pMags set with jumper in.

Last trip at 13.5K’ the plane steadied out at 174 knots TAS burning 7.5GPH.

Carl
 
I now have several long cross countries on the new RV-8. Doing data runs as part of Phase 1 I found the plane has a sweet spot at 13K’ - 14k’. I run LOP exclusively.

I've done a lot of efficiency testing on mine at altitude, and my efficiency curve is pretty flat (and reverses) between 13 and 17 - so you're right on the mark there.
 
I use LOP for x-country regularly. I took this photo the other day...171 KTAS on 6.3 GPH in my RV-8.
 

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I have too much spread in EGT between the cylinders on my IO-320 to run LOP without getting GAMI injectors. The engine runs a little rough at that setting, and I'm not convinced that that would be a cost-effective upgrade at this point. As it is, I fly mostly at 60-65% power to stay out of the "red box". GAMI injectors are a ways down on my priority list.
 
I have too much spread in EGT between the cylinders on my IO-320 to run LOP without getting GAMI injectors. The engine runs a little rough at that setting, and I'm not convinced that that would be a cost-effective upgrade at this point. As it is, I fly mostly at 60-65% power to stay out of the "red box". GAMI injectors are a ways down on my priority list.

No need for GAMI injectors. Do a GAMI run, find fuel flow when each cylinder peaks, then replace the rich cylinders (the ones that peaked late) with slightly smaller injectors. Replacement injectors are available from Air Flow Performance in 0.0005” increments (~$28 each). I replaced two injectors to get a GAMI spread of 0.1GPH.

Call Don at AirFlow Performance - he can help.

Carl
 
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For those that are not experienced at LOP operations, two things are important.

1) you have to have enough engine instrumentation to see what is going on. Individual CHT and EGT probes for each cylinder, and fuel flow.

2) you have to have some technical understanding of what you are doing when you lean to peak, lean beyond peak to the LOP regime.

Nowadays, most of us have #1. That was not so true 20 years ago, and there are probably still RVs around that were built long ago that don't have engine analyzers.

The published "Pelican Perch" series on LOP operations by John Deakin should be required reading.
 
So many folks now understand and fly LOP that I'm curious why Ross brought this up today? Did he make some popcorn and hope for a "primer wars" discussion?

I do still run into mechanics that shake their heads and say "we love LOP guys, good for our business. We replace a lot of cylinders." My answer is always that it is not the LOP operation that is the problem.

One mechanic showed me some spark plugs where the center electrode was kind of pitted and shiny, almost looked like it had melted and flowed a little bit. I said that is not from running LOP, that is from running on the verge of detonation. He said, "same thing". I just shook my head and walked away.
 
LOP

So many folks now understand and fly LOP that I'm curious why Ross brought this up today? Did he make some popcorn and hope for a "primer wars" discussion?

It was due to a side discussion that came up in the Surefly Ignition thread and concerns about “oxidation damage” when LOP...

Skylor
 
I have too much spread in EGT between the cylinders on my IO-320 to run LOP without getting GAMI injectors. The engine runs a little rough at that setting, and I'm not convinced that that would be a cost-effective upgrade at this point. As it is, I fly mostly at 60-65% power to stay out of the "red box". GAMI injectors are a ways down on my priority list.

Balancing your injectors can be done usually for less than 60 bucks. Call Don Rivera at AirFlow Performance. I did mine with one ($28.00) injector. Very rarely more than 2 are required. Doesn’t take but a few hours LOP to break even.
 
LOP to get there faster

This may be unique to the -10 where, IMHO, the standard 60 gal fuel tanks are a bit small for an IO540. But I fly a certain number of trips which are 4 hours or so (and a few very long trips) where flying LOP (160 ktas, 10 g/hr) gets me to the destination sooner than flying best power mixture (174 ktas, 14 g/hr) - because I don’t need a fuel stop. And I save gas money, and keep CHTs cool too. What’s not to like? And on shorter trips, the time difference is less than 15 minutes. BTW, this is a stock IO540, with two mags. Only mod is to tweak injector nozzles with ones from Don/Air Flow (I think I changed three). The engine runs so smoothly that I can just keep pulling out the mixture until engine power is so low that the plane won’t maintain altitude, you think the engine has quit, but in fact it’s running at very low power.
 
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No need for GAMI injectors. Do a GAMI run, find fuel flow when each cylinder peaks, then replace the rich cylinders (the ones that peaked late) with slightly smaller injectors. Replacement injectors are available from Air Flow Performance in 0.0005” increments (~$28 each). I replaced two injectors to get a GAMI spread of 0.1GPH.

Call Don at AirFlow Performance - he can help.

Carl

Balancing your injectors can be done usually for less than 60 bucks. Call Don Rivera at AirFlow Performance. I did mine with one ($28.00) injector. Very rarely more than 2 are required. Doesn’t take but a few hours LOP to break even.

Good tip...I'll look into that. Thanks.
 
LOP

Depends on the mission of the day, but have been running LOP successfully about 15 years now on a number of planes. It takes a engine monitor and some understanding to do it correctly. Not lean enough at high power settings can be destructive.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
I've seen some comments here on VAF and some of my YT vids basically saying "ok you're going slower so of course you burn less fuel".

If we look at the data from the Bonanza video and run the numbers we see the lower speed would require 19% less hp but fuel burn LOP is dropping 28%. I've seen similar numbers on the RV-10 comparing ROP to LOP.

On turbo engines, the recommendation is to go LOP and then recover the lost speed by increasing MAP a couple inches. Same speed, a lot lower fuel burn is the result. We can't do that with atmo engines but we can still save a decent amount of fuel if we are willing to accept a bit more time for the trip.
 
I have too much spread in EGT between the cylinders on my IO-320 to run LOP without getting GAMI injectors. The engine runs a little rough at that setting, and I'm not convinced that that would be a cost-effective upgrade at this point. As it is, I fly mostly at 60-65% power to stay out of the "red box". GAMI injectors are a ways down on my priority list.

GAMI will be expensive. Call Don Rivera at Airflow Performance. He has injectors with replaceable restrictors. You can tune it yourself. Depending on how old your injectors are, they may already have restrictors that you can replace at ~$28 ea.

Ed Holyoke
 
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If we look at the data from the Bonanza video and run the numbers we see the lower speed would require 19% less hp but fuel burn LOP is dropping 28%. I've seen similar numbers on the RV-10 comparing ROP to LOP.

ROP and LOP are terms with no dimensions. Might be better to attach numerical values to our descriptions, for example "comparing 150 ROP to 50 LOP".
 
ROP and LOP are terms with no dimensions. Might be better to attach numerical values to our descriptions, for example "comparing 150 ROP to 50 LOP".

Agree. Our testing has shown best economy at somewhere between 30 and 60 LOP (16-17 AFR), best power at around 100-125 ROP (12.5-13.5 AFR). The best power area is pretty flat as the video illustrates.

Note that we are varying timing as well as AFR so I expect results will be slightly different with fixed timing.

Does your testing agree with this data?
 
Agree. Our testing has shown best economy at somewhere between 30 and 60 LOP (16-17 AFR), best power at around 100-125 ROP (12.5-13.5 AFR). The best power area is pretty flat as the video illustrates.

Note that we are varying timing as well as AFR so I expect results will be slightly different with fixed timing.

Does your testing agree with this data?

Everyone's testing agrees with this data...including Lycoming. It's straight from the standard "Leaning Relationships" chart. Note the midline of the "Best Economy" range.
 

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Here's one with AFR (from another Lyc document) inserted per reference to EGT. 16~17 AFR, yes sir.
.
 

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...snip

On turbo engines, the recommendation is to go LOP and then recover the lost speed by increasing MAP a couple inches. Same speed, a lot lower fuel burn is the result. We can't do that with atmo engines but we can still save a decent amount of fuel if we are willing to accept a bit more time for the trip.

I think this is what the R-3350 Turbo Compound manual referred to as "BMEP Recovery"

Everyone's testing agrees with this data...including Lycoming. It's straight from the standard "Leaning Relationships" chart. Note the midline of the "Best Economy" range.

For anyone that ever said "Lycoming doesn't embrace LOP"...there they are providing LOP data right in their manual!

Skylor
 
I'm happy to take the approx 1gph penalty to go faster, run smoother, simplify system, no BU bat needed, etc...

Your experience with LOP ops is "what it is", but considering your fixed timing magnetos, not unexpectedly "less than compelling".

I've seen the speed sag with LOP ops many, many times, but I've also seen the very obvious recovery with activation of the LOP advance feature on the SDS product line. It's a compelling thing in real life. Now that I am EFI, the "LOP feature" pulls mixture and simultaneously adds advance with the flip of a switch. This manifests itself without the obvious speed sag and then recovery - flipping the switch simply changes fuel flow. In my case, I'll reach cruise at TOC and stabilize at 197 KTAS (ROP). Flipping the switch results in nothing but a reduction in FF by about 3 -4 GPH AT THE SAME TAS. Granted, I'm not tuned as tightly as I will be later in the flight test period, but once again, ignition timing is a HUGE influence on LOP ops. If you are stuck with fixed timing for ROP and LOP ops, you are leaving a lot of performance on the table. That's on you, not the mode of operation.
 
Now that I am EFI, the "LOP feature" pulls mixture and simultaneously adds advance with the flip of a switch. This manifests itself without the obvious speed sag and then recovery - flipping the switch simply changes fuel flow. In my case, I'll reach cruise at TOC and stabilize at 197 KTAS (ROP). Flipping the switch results in nothing but a reduction in FF by about 3 -4 GPH AT THE SAME TAS.

Quite a claim. If you can make the same power on 3~4 less GPH merely by advancing the timing, why bother running ROP? It seems you've made "Best Power" mixture entirely superfluous.
 
Quite a claim...


Please read the rest of my statement - I still have some tuning to do (my "best power" programming is likely still fat), but I'm close enough to show that ignition advance makes a huge impact on LOP power. This is to counter the "real world experience" of those whose only LOP experience is NA engines and magnetos - and the understandable disappointment of the significant loss in speed.

I know better than to claim ignition advance will recover all the power that is lost to LOP ops (it's not possible in the physical universe we occupy), but ignition advance pulls a LOT back compared to fixed timing optimized for ROP ops. That's a demonstrated fact.
 
We see about 4-5 knots come back on the RV-10, depending on how far LOP we are.

Have some Lancair customers reporting 7 more knots over their mags when 50 LOP.

Flame speed is 30% slower at 17 AFR roughly. PCP will occur late if you don't advance the timing.
 
"Flipping the switch results in nothing but a reduction in FF by about 3 -4 GPH AT THE SAME TAS."

Mike, nothing in the rest of your statement contradicts or expands on the above. Seriously, you're not doing Ross any favors.
 
We see about 4-5 knots come back on the RV-10, depending on how far LOP we are.

Have some Lancair customers reporting 7 more knots over their mags when 50 LOP.

Flame speed is 30% slower at 17 AFR roughly. PCP will occur late if you don't advance the timing.

Another post that makes me wish there was a "like" button.

I was out doing some propeller testing yesterday, using best-power mixture (actually peak EGT, so a little leaner than best power) and one of the data points matched my normal cruise condition, except for the mixture.
Normally at WOT, 2400 RPM, 50 LOP cruise I get about 168-169 kts at 8000 ft. Yesterday with everything the same except mixture at peak EGT, I got 175 kt. So that is the speed loss for me to cruise LOP. That 6 kt speed reduction also brings a 1.5 GPH fuel flow reduction. So my MPG goes up from 21 to 24.
Flight time on my typical 1:45 mission is increased by 4.2 minutes.
 
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Normally at WOT, 2400 RPM, 50 LOP cruise I get about 168-169 kts at 8000 ft. Yesterday with everything the same except mixture at peak EGT, I got 175 kt. So that is the speed loss for me to cruise LOP. That 6 kt speed reduction also brings a 1.5 GPH fuel flow reduction.

I have a similar peak vs 50 LOP delta, although both speeds are higher. Photo below was taken this AM on the way to Columbus MS, at peak EGT, solo, half fuel, TAS 185.

Note oil temp and CHT; the exit air door is fully closed. I aimed for a design point of 59F as a max OAT with a closed door back when I was iteratively sizing the exit area. Ended up around 30 sq in.

Steve, what ignition type and timing are you using with your angle valve 360?
.
 

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"Flipping the switch results in nothing but a reduction in FF by about 3 -4 GPH AT THE SAME TAS."

Mike, nothing in the rest of your statement contradicts or expands on the above. Seriously, you're not doing Ross any favors.

I'm not sure what you are looking for here Dan. I'm reporting what I see - no "spin", not trying to appease anyone.

I get to TOC in a mixture condition that is "close" (but not completely sorted yet) to best power, I stabilize at 197KTAS and 15 GPH, then flip the LOP switch.

Result: FF drops to 11 GPH, speed stays the same.

Period. Dot.


If you are looking for data from a a calibrated test boom and fuel flow totalizer before my post has any validity, you will be waiting a long time.
 

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You have a fast plane Dan. These are great numbers.

Curious how much speed would you lose here if you opened the cowl flap fully?
 
Here is a graphical representation of combustion flame speed vs. AFR. This shows why fixed timing can't be optimized at both ROP and LOP. You'll lose some power on one or the other ends of the mixture range.
 

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I have a similar peak vs 50 LOP delta, although both speeds are higher. Photo below was taken this AM on the way to Columbus MS, at peak EGT, solo, half fuel, TAS 185.

Note oil temp and CHT; the exit air door is fully closed. I aimed for a design point of 59F as a max OAT with a closed door back when I was iteratively sizing the exit area. Ended up around 30 sq in.

Steve, what ignition type and timing are you using with your angle valve 360?
.

Wow you are fast.

I have one LSE Plasma II with static timing of 25 BTDC, and one Slick mag with static timing of 25 BTDC. The Lightspeed map goes as far as 39 BTDC IIRC, but not at normal cruising MAP, RPM.

I'm quite sure that I will gain some speed by reducing cowl exit. It is stock now. I have been holding off waiting to get baseline data IAW your white paper first. I also need to improve my oil cooler ducting so that I can keep oil cool when I close the exit down. With Covid, I just haven't found a back-seater to help. I don't have a pitch autopilot, so flying, swapping tubes on the manometer, writing numbers down, it was more workload than I liked.
 
Different Mixtures for Different Needs

I use different mixtures for different needs.

In this first photo, I'm cruising at 15,500 running ROP and high (2600) RPM. 180 KTAS on 8.3 gallons per hour. The plane was loaded with a passenger and lots of luggage. The speeds were helped by cool OAT (~ 0C) and the fact that the plane was in "race mode" with 1 radio antenna removed from the belly, race wingtips that I thought would hurt my heavy, high altitude performance but actually seemed to help based on other testing, and a few other minor details. I was running rich of peak and high RPM to recover horsepower lost my the low manifold pressure of 16.7 inHg.

915EF707-6443-49A0-95E9-2536EDB644E5.jpeg


In this second image which I've shared before, I'm loafing around down low at high manifold pressure, very LOP, and very low RPM to make up for my fixed timing with the lean mixture. I usually cruise at low altitude LOP, using mixture and RPM instead of throttle to control the power. The engine runs clean, cool, and reasonably efficient this way. Here I'm at 27.1 inHg, 1870 RPM and 6.1 GPH.

IMG_5436small.jpg


Skylor

p.s. Does anyone know why the second images is rotated horizontally in internet explorer, but displays normally in firefox when viewed on my laptop?
 
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In this second image which I've shared before, I'm loafing around down low at high manifold pressure, very LOP, and very low RPM to make up for my fixed timing with the lean mixture. I usually cruise at low altitude LOP, using mixture and RPM instead of throttle to control the power. The engine runs clean, cool, and reasonably efficient this way. Here I'm at 27.1 inHg, 1870 RPM and 6.1 GPH.

IMG_5436small.jpg

Wow, I don't mind running somewhat over-square, but wow. The Lycoming operating manual has curves of Hp for various combinations of MAP and RPM. The 27" MAP line extends down to about 2400 RPM IIRC.
 
Dave Anders often runs very low RPM in cruise getting some pretty incredible numbers. Low RPM cuts engine frictional losses quite a bit.

Does anyone have any data on how high MAP/ low RPM affects engine life?
 
Dave Anders often runs very low RPM in cruise getting some pretty incredible numbers. Low RPM cuts engine frictional losses quite a bit.

Does anyone have any data on how high MAP/ low RPM affects engine life?

Again, numbers would help understanding. Skylor said 27". Is Dave running high MP, or cruising at altitude, with low MP? Apple and orange.

Likewise, "engine life" is very general. Like ignition timing, one size does not fit all. The long term result may be quite different for cranks with and without pendulum absorbers. Has anyone in the propeller business extended a blade vibration survey to the extreme oversquare regime?

I'm not saying it's bad. I'm saying God is in the details.
 
Wow you are fast.

Believe it or not, that photo was taken with the gun pod hanging on the right wing. Beginners luck mostly.

I have one LSE Plasma II with static timing of 25 BTDC, and one Slick mag with static timing of 25 BTDC. The Lightspeed map goes as far as 39 BTDC IIRC, but not at normal cruising MAP, RPM.

If I may suggest, next time you're in there reset the mag to 23, and the Lightspeed base to 20. Please let me know the results.

I'm quite sure that I will gain some speed by reducing cowl exit. It is stock now. I have been holding off waiting to get baseline data IAW your white paper first. I also need to improve my oil cooler ducting so that I can keep oil cool when I close the exit down.

As you know I have the oil cooler ducted to a spot in the roof of the exit bell. I did do an early check flight with the cooler exit ducting removed, and as expected, oil temperature was significantly higher due to reduced deltaP.

BTW, my oil temp sender seems to read about 7F high, by comparison to all the other temp sensors when parked in the hangar after a period of steady OAT.
 
Again, numbers would help understanding. Skylor said 27". Is Dave running high MP, or cruising at altitude, with low MP? Apple and orange.

Likewise, "engine life" is very general. Like ignition timing, one size does not fit all. The long term result may be quite different for cranks with and without pendulum absorbers. Has anyone in the propeller business extended a blade vibration survey to the extreme oversquare regime?

I'm not saying it's bad. I'm saying God is in the details.

Dave is virtually always WOT, controlling power with RPM. Altitude and power setting is decided by mission, weather and O2 use.

By life, I mean, is typical TBO impacted? Nobody is going to do this if it's known by facts that life goes from 2000 to 200 hours. Not looking for speculation here. Any known studies by someone like Lycoming where continuous oversquare operation has been tested?
 
High MP

Again, numbers would help understanding. Skylor said 27". Is Dave running high MP, or cruising at altitude, with low MP? Apple and orange.

Likewise, "engine life" is very general. Like ignition timing, one size does not fit all. The long term result may be quite different for cranks with and without pendulum absorbers. Has anyone in the propeller business extended a blade vibration survey to the extreme oversquare regime?

I'm not saying it's bad. I'm saying God is in the details.

The primary issue normally caused by low RPM at high MPs is high peak cylinder pressures. This can cause several issues including high CHTs, detonation, pendulum absorber harmonics and failure, crank and prop harmonics, etc.

The key though is understanding why the high cylinder pressures occur at low RPM and high MP. Under “normal” ROP mixtures in this case, the cylinder combustion event happens too fast resulting in peak pressures occurring while the piston is still near the top of its stroke and before the crankshaft has rotated very far past the top dead center position. In this area, the cylinder volume is still quite small and the piston is still moving rather slowly away from TDC resulting in a slow rate of cylinder volume expansion. BTW, the angle of crankshaft rotation past TDC where peak cylinder pressure occurs is known as theta-PP. Anyway, when the peak combustion event pressure occurs shortly after TDC (or small theta-PP) the pressure tends to get very high which results in high connecting rod and crankshaft forces. This high pressure also compresses the insulating boundary layer of gas that typically exists along the combustion chamber walls resulting in higher heat transfer into the cylinder, cylinder head, and piston thus causing elevated cylinder and oil temperatures .

Now the above issues are not typically a problem with low density mixtures because their slower burn rate results in a larger theta-PP and lower peak pressures. Historically, manifold pressure has been the tool used to gauge charge density and power levels, hence the reason for recommendations of manifold pressure limits at (or below) certain RPM’s.

However, even at high manifold pressures, if the combustion mixture is very lean (i.e well lean of peak), then we have a slow combustion event that behaves similarly to lower manifold pressure settings. In the case that I posted above, I am running more than 100 degrees LOP. The low cylinder head and oil temperatures on a 90 degree day provide good evidence that the peak cylinder pressures were remaining low in this scenario.

Skylor

p.s. Typed from my phone and not proofread....
 
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Yes great post covering the important aspects.

I'd have to think that forces on the connecting rod are of little concern on a Lycoming. Peak CP and BMEP not too high to begin with and the rods are well proven to handle at least double the normal cylinder pressures on Reno race engines- although those don't go 2000 hours between overhauls either.
 
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Good post Sky.

Ya'll note the very lean mixture with fixed ignition timing, thus the late thetaP which makes it all possible. In theory a variable EI would hold base timing given 27" MP, but we have seen some MP sensor failures default at least one brand to full advance.
 
I'm quite sure that I will gain some speed by reducing cowl exit. It is stock now.

After a lot of work, testing, and two reduced area exits, I got no improvement from the exit area reduction. Just increased lower plenum pressures and warmer oil temperatures. It even reduced cross sectional area. I still have no clue as to why this result occurred.
 
Good post Sky.

Ya'll note the very lean mixture with fixed ignition timing, thus the late thetaP which makes it all possible. In theory a variable EI would hold base timing given 27" MP, but we have seen some MP sensor failures default at least one brand to full advance.

Ditto.

My first thought was that this is like letting out the clutch and going WOT on a 4 cylinder engine at 1800 RPM. Some lighter-built car engines (like my Miata) would really "lug" and you would feel the strange vibration. But of course when you do that in a car, you get a rich mixture for the acceleration.

Skylor's explanation of utilizing the very lean mixture makes good sense.
 
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