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PT20J

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1 hour ago, Shadrach said:

Sort of.  As it has been explained to me by folks with access to far more sophisticate equipment and experience, if you were to graph the cylinder pressure across the power stroke you would see a sharp peak and decrease in pressure on the rich side and a less drastic peak and less drastic decrease on the lean side. Put simply, for the same mean pressure across the power stroke, ROP generates pressures far above and below the mean while LOP pressures cluster closer to mean throughout the power stroke.

One can see this in simple flight testing. Set up power for an attainable airspeed on either side of the mixture spectrum (all other things being equal). Record CHTs for that airspeed at ROP and LOP.  CHTs will be lower on the lean side. How much so depends on the power setting.

Here's what I think is going on. When you adjust the mixture from best power to LOP at a constant throttle setting, the power decreases. Part of the reason for the power decrease is the engine is simply consuming less fuel. This is partially offset by fact that BSFC is lower LOP so the engine is more efficient. Also, the slower burning mixture means that the ignition timing is no longer set for MBT (maximum brake torque). The combination of the timing not being optimum and the improved efficiency leads to less heat rejection to the cylinders which shows up as lower CHTs. Now if you open the throttle to get back the power lost, you still have the increased efficiency and the timing is still off optimum, so you still get lower CHTs. If you were able to adjust the timing back closer to MBT you would get more power the CHTs would increase some. This is why people have reported higher CHTs with a Surefly running in advanced timing mode.

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12 minutes ago, Freemasm said:

Not quite but you're in the right mindset. Briefly, knocking is detonation/supersonic combustion/an explosion; however you want to think about it. A sonic boom is a sound wave that crosses over you (A sound wave is a pressure wave before anybody starts to get too excited). The wave is very thin; almost a discontinuity. Because the wave is so thin, it is perceived as an explosion. Anyway, the subject pressure wave(s) is shed from the surface of objects traveling faster than the speed of sound; cool aircraft, most bullets.  There's typically more than one shock wave shed from complex shapes like aircraft. The strongest ones are usually associated with wing leading edges. This one tends to mask all of the weaker ones. These waves come off at different angles (Mach Shock Angle). The coolest example here would be the space shuttle. It shed two very strong shock waves; one from the nose (it was a lifting body. Not the most aerodynamic but had to withstand atmosphere re-entry. Anyway, these two very strong shocks came off at such different angles there's quite a distance between them when they make it to the ground. An observer could definitely hear both strong "booms". 

So much for a dump out of the way-back machine. Cheers boys.  

and I thought I was a nit picker...

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Just now, PT20J said:

Here's what I think is going on. When you adjust the mixture from best power to LOP at a constant throttle setting, the power decreases. Part of the reason for the power decrease is the engine is simply consuming less fuel. This is partially offset by fact that BSFC is lower LOP so the engine is more efficient. Also, the slower burning mixture means that the ignition timing is no longer set for MBT (maximum brake torque). The combination of the timing not being optimum and the improved efficiency leads to less heat rejection to the cylinders which shows up as lower CHTs. Now if you open the throttle to get back the power lost, you still have the increased efficiency and the timing is still off optimum, so you still get lower CHTs. If you were able to adjust the timing back closer to MBT you would get more power the CHTs would increase some. This is why people have reported higher CHTs with a Surefly running in advanced timing mode.

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A lot more to the story than ROP and LOP. The fuel specifics are better LOP because air is being used to slow the combustion event rather than excess fuel. 

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31 minutes ago, Shadrach said:

A lot more to the story than ROP and LOP. The fuel specifics are better LOP because air is being used to slow the combustion event rather than excess fuel. 

Here's how Prof. Heywood (Internal Combustion Engine Fundamentals, 1988p 831) explains it:

"Combustion of mixtures leaner than stoichiometric produces products at lower temperature, and with less dissociation of triatomic molecules CO2 and H2O. Thus the fraction of the chemical energy of the fuel which is released as sensible energy near TC is greater; hence a greater fraction of the fuel's energy is transferred as work to the piston during expansion, and the fraction of the fuel's available energy rejected to the exhaust system decreases."

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1 hour ago, Freemasm said:

Not quite but you're in the right mindset. Briefly, knocking is detonation/supersonic combustion/an explosion; however you want to think about it. A sonic boom is a sound wave that crosses over you (A sound wave is a pressure wave before anybody starts to get too excited). The wave is very thin; almost a discontinuity. Because the wave is so thin, it is perceived as an explosion. Anyway, the subject pressure wave(s) is shed from the surface of objects traveling faster than the speed of sound; cool aircraft, most bullets.  There's typically more than one shock wave shed from complex shapes like aircraft. The strongest ones are usually associated with wing leading edges. This one tends to mask all of the weaker ones. These waves come off at different angles (Mach Shock Angle). The coolest example here would be the space shuttle. It shed two very strong shock waves; one from the nose (it was a lifting body. Not the most aerodynamic but had to withstand atmosphere re-entry. Anyway, these two very strong shocks came off at such different angles there's quite a distance between them when they make it to the ground. An observer could definitely hear both strong "booms". 

So much for a dump out of the way-back machine. Cheers boys.  

I lived in the Valley for over a decade, during which time the Shuttle was still flying.  I cannot recall how many times the Shuttle was diverted to Edwards, and we would hear the double boom as it flew over us.  Could not see the Shuttle, but even within the office, we could definitely hear it.  

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2 hours ago, PT20J said:

Here's how Prof. Heywood (Internal Combustion Engine Fundamentals, 1988p 831) explains it:

"Combustion of mixtures leaner than stoichiometric produces products at lower temperature, and with less dissociation of triatomic molecules CO2 and H2O. Thus the fraction of the chemical energy of the fuel which is released as sensible energy near TC is greater; hence a greater fraction of the fuel's energy is transferred as work to the piston during expansion, and the fraction of the fuel's available energy rejected to the exhaust system decreases."

No doubt Prof. Heywood has far more knowledge on the subject than me. I certainly don't dispute any of the above.  However, if what you said earlier about ignition timing being outside the realm of MBT when LOP, then how is the scenario in the picture below possible? Bore, Stroke, compression ratio, RPM, ignition timing and cowl design are all the same. The only differences between these two engines making the same power is MP and FF.  Now maybe George and Ken are trying to pull a fast one by not showing the pilot standing on the rudder but I tend to believe that it is indeed possible to run the same speed on considerably less fuel and lower temps on the lean side of peak all other things besides MP and FF being equal.  I don't think that would be the case if timing were as far from optimal as you suggest.  It may be the case that the 2300rpm depicted in the photo is the sweet spot where this is possible.  I don't know.  What I do know from a practical standpoint is that mixture management is about controlling the speed of the combustion event and that can be done with excess air or excess fuel.  What I choose to use is dictated by a number of factors.  With a NA engine, I try to fly as close to peak EGT as possible because it is the highest power setting possible at bottom of BSFC curve.  If peak looks like it's going to be on the hot side, I introduce a touch more air.  If I am at higher altitudes where air is in short supply, I use fuel to control the combustion event.  I try to keep it about that simple when explaining my engine management operations it to others (some still go cross-eyed...especially experienced ATPs that fly POH numbers only).  Also to bring this back to another thread, I don't see a dramatic reduction in speed between 100ROP and 10-20LOP (maybe 6kts) and I think this may be due to the fact that my engine is timed to 25°.

image.png.a1695ba4c481ed2e2919809002924110.png

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41 minutes ago, Shadrach said:

No doubt Prof. Heywood has far more knowledge on the subject than me. I certainly don't dispute any of the above.  However, if what you said earlier about ignition timing being outside the realm of MBT when LOP, then how is the scenario in the picture below possible? Bore, Stroke, compression ratio, RPM, ignition timing and cowl design are all the same. The only differences between these two engines making the same power is MP and FF.  Now maybe George and Ken are trying to pull a fast one by not showing the pilot standing on the rudder but I tend to believe that it is indeed possible to run the same speed on considerably less fuel and lower temps on the lean side of peak all other things besides MP and FF being equal.  I don't think that would be the case if timing were as far from optimal as you suggest.  It may be the case that the 2300rpm depicted in the photo is the sweet spot where this is possible.  I don't know.  What I do know from a practical standpoint is that mixture management is about controlling the speed of the combustion event and that can be done with excess air or excess fuel.  What I choose to use is dictated by a number of factors.  With a NA engine, I try to fly as close to peak EGT as possible because it is the highest power setting possible at bottom of BSFC curve.  If peak looks like it's going to be on the hot side, I introduce a touch more air.  If I am at higher altitudes where air is in short supply, I use fuel to control the combustion event.  I try to keep it about that simple when explaining my engine management operations it to others (some still go cross-eyed...especially experienced ATPs that fly POH numbers only).  Also to bring this back to another thread, I don't see a dramatic reduction in speed between 100ROP and 10-20LOP (maybe 6kts) and I think this may be due to the fact that my engine is timed to 25°.

I don't disagree with anything you said. And I would never accuse George Braly of cooking the books. I only quoted Prof. Heywood to offer an explanation for why the efficiency is better LOP.

As for MBT timing, it would normally be set for the max. power mixture, perhaps backed off a bit if necessary to increase detonation margin. Any other mixture will have a slower burn rate and that will make the ignition point non-optimum. BUT... the optimum is very broad. Timing can be off by +/- 5 degrees and not have much affect on power. Running deeply LOP probably throws it off more, but that probably only contributes to perhaps a few percent power loss. I should have pointed that out in my original comment. 

I absolutely agree that you can run LOP and generate the same power with lower fuel consumption compared to ROP. The problem is, with a normally aspirated engine, the LOP power available drops off so quickly with fuel flow that you are limited to very low power settings or very low altitudes. With a turbocharged engine, there are more options. There are also more opportunities to screw up. With my little IO-360, after a few thousand feet, there is no red box to be concerned about. With a turbocharged engine, the red box is always lurking.

I run my engine pretty much the same as you do. If I'm low and just fooling around and not in a hurry to get anywhere, I'll run it LOP. But I live in the Pacific NW where it's hard to go anywhere without climbing over a mountain. So when I'm traveling, I usually run peak for best tradeoff (for me) of speed and efficiency. At peak EGT fuel flow, my 64 gallon tanks will last longer than I care to sit in a little airplane in one stretch and I figure I pre-saved on fuel by not buying a big-engined airplane, so I don't really need the extra economy of LOP.

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4 hours ago, Shadrach said:

No doubt Prof. Heywood has far more knowledge on the subject than me. I certainly don't dispute any of the above.  However, if what you said earlier about ignition timing being outside the realm of MBT when LOP, then how is the scenario in the picture below possible? Bore, Stroke, compression ratio, RPM, ignition timing and cowl design are all the same. The only differences between these two engines making the same power is MP and FF.  Now maybe George and Ken are trying to pull a fast one by not showing the pilot standing on the rudder but I tend to believe that it is indeed possible to run the same speed on considerably less fuel and lower temps on the lean side of peak all other things besides MP and FF being equal.  I don't think that would be the case if timing were as far from optimal as you suggest.  It may be the case that the 2300rpm depicted in the photo is the sweet spot where this is possible.  I don't know.  What I do know from a practical standpoint is that mixture management is about controlling the speed of the combustion event and that can be done with excess air or excess fuel.  What I choose to use is dictated by a number of factors.  With a NA engine, I try to fly as close to peak EGT as possible because it is the highest power setting possible at bottom of BSFC curve.  If peak looks like it's going to be on the hot side, I introduce a touch more air.  If I am at higher altitudes where air is in short supply, I use fuel to control the combustion event.  I try to keep it about that simple when explaining my engine management operations it to others (some still go cross-eyed...especially experienced ATPs that fly POH numbers only).  Also to bring this back to another thread, I don't see a dramatic reduction in speed between 100ROP and 10-20LOP (maybe 6kts) and I think this may be due to the fact that my engine is timed to 25°.

image.png.a1695ba4c481ed2e2919809002924110.png

I look at it this way:

1.  As to the demo you showed, the peak pressure point may not be much different between the two engines.  LOP slows the combustion process and moves PP further past TDC.  However, they recovered power by increasing MP.  Higher MP burns faster so it moves PP closer to TDC.  The net result may be very little change in PP point.

2.  I am probably wrong, but try to think of efficiency of burn this way.

a.  At peak EGT the mixture burns as fast as possible but the mixture is not an idea mixture.  That is, one area may have too much fuel for the oxygen available and another may have too much oxygen for fuel available.  So even though theoretically all the fuel will be burned and no oxygen will be left, in reality there is a little unburned or partially burned fuel and a little oxygen going out the tail pipe.

b.  As I continue to lean and go LOP, I am supplying the engine with more oxygen than is needed to burn all the fuel.  As I continue to lean, it becomes less and less likely that any fuel molecule will escape without being burned.  I capture a little higher percentage of available energy (even though the total energy is decreasing).  However, since I'm LOP, the burn rate slows, PP moves further past TDC, and becomes somewhat less effective.  However, at least when I'm close to peak EGT, PP hasn't moved too far so the BSFC improves.  As I continue to go deeper LOP, there is less and less unburned fuel so I'm not capturing any previously unused energy but PP continues to move further away from ideal so efficiency (BSFC) starts getting worse.  That's why we don't want to run too deeply LOP if we are looking for best BSFC.

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Hmmmmmm.....

1) I’m a fan of flying quickly... and efficiently.

2) I have an NA engine... limited in MP at the alts that I use... somewhere near 20”

3) 10k -12.5k’... depending on the day...

4) The red box faded away a couple of thousand feet below...

5) Peak EGT generally turns a high percentage of gasoline into power... where ROP does not...

6) Efficiency of burning all of the gasoline increases as I go a touch more LOP... but not too much or collisions of O2 and gasoline become accidentally more rare... and my power/FF will be dropping exponentially...

7) I could improve the time allowed for the combustion completion... by slowing the piston speed down... using the blue knob to reduce rpm... 

8) Slowing the RPM is against my rule of Speed...  so, 2500 - 2550 becomes my preferred cruise rpm... :)

9) Following this outline I have two modes of cruise...  (from fuzzy memory)

ROP: 15gph, 175kts... 2500rpm...  Max MP  (100°F ROP)

LOP: 12.5gph 165kts... 2500rpm... Max MP (2°F LOP)

10) If I had a pair of snails...( TNs)... Max MP would get raised until the peak EGT would use 15gph, somewhere around 24”(?)

11) This would be more like operating at 6-8k’...  but having the drag of 10-12k’...

12) The red box still needs to be respected... as it is close... (add another 1-2” of MP for additional cooling)

13) Everything is good until it isn’t...   a speck stuck in a fuel injector may cause a problem...

14) Wait, there is hope... at peak... an FI with a blockage... is going to go more LOP than everything else... :)

15) No mechanical hazard with that... even a lazy scan of the JPI will notice it in time...

16) Summary...

  • I see a 10kts difference between ROP and barely LOP...
  • I see a couple of gallons per hour saved...
  • The engine stays cleaner LOP...
  • The CHTs stay cooler...
  • Given an extra 50rpm, I use it... to produce more power... at the cost of another gph or so...
  • No fear of of cylinder misbehavior... unless something really goes awry...

17) Given the opportunity of variable timing... mine is currently 22°BTDC... I would enjoy going further BTDC if able...

PP thoughts only...

Best regards,

-a-

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Combustion of hydrocarbons in an engine is a complex process, but there are a few key points that really helped me to understand it:

1. Combustion is actually a chemical chain reaction comprising several processes that each have finite reaction times. If the mixture is homogeneous and sufficient time is available for the reactions to run to completion, a stoichiometric air-fuel ratio will have the fastest burn rate, produce the most heat and the products will be CO2 and H2O. If the combustion process does not complete, then other intermediate products will be present in the exhaust, primarily CO. Rich mixtures generally combust incompletely because the process runs out of oxygen, but rich mixtures produce more power and heat because all the available oxygen (the limiting factor since the engine can only pump so much air) is consumed. Lean mixtures are more efficient because they burn up all the fuel due to an excess of oxygen, but produce less power because there is less fuel to burn.

2. At high temperatures, dissociation occurs. This can be thought of as the combustion process running in reverse where some of the products recombine to form reactants. Since the highest temperatures are produced with a stoichiometric mixture, that's also where the maximum dissociation occurs. Dissociation frees up O2 and this can be used to burn extra fuel if it's available. This increases the temperature and contributes more molecules of combustion products to the combustion gases. This is why the maximum CHT occurs at a fuel-air mixture richer than stoichiometric (because burning the extra fuel releases more heat) and also why the maximum power is developed at mixture that is richer still (because the extra molecules of combustion products act to increase the pressure).

3. Turbulence in the cylinder increases combustion rate. Greater piston speed produces greater turbulence. This is why, over the small range of rpm available for cruise power settings, the rpm doesn't change combustion timing much.

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Yay....

We have reached the point where droplet size matters...

Evaporation rate matters...

Mixing O2 with gasoline at the molecular level matters... even with all that other N2 and CO2 that try to get in the way...

 

We kind of get a coarse spray from our fuel injectors...  

where our fuel doesn’t get warmed very much...

Any benefit to changing the tried and true standard of today? Finer spray?

Heating the mixture may provide a more uniform mixture for better burning...

But, would make it more difficult to stuff more into an NA engine...

 

PP thinking out loud only...

Best regards,

-a-

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Perhaps the Biggest reason why LOP can reduce fuel consumption is the basic operating principle of how an internal combustion engine operates.

‘Engines do not develop power from the pressure from “explosions” as many think, they develop power from the rapid expansion of heating a gas (air)

Within reason of course if you reduce the ratio of air to fuel and still generate the heat, your increasing the amount of gas to expand when compared to the amount of fuel it takes to expand it.

Fuel enrichment at high power isn’t so much to do with being required to make the power, it’s required to make the power without overheating the engine

‘Those of you that are bumping the timing up are playing with fire, I disagree with the plus or minus 5 degrees of timing won’t make much difference, it will make big differences, increasing timing will certainly increase power, but your reducing your margin for detonation.

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9 hours ago, carusoam said:

Yay....

We have reached the point where droplet size matters...

Evaporation rate matters...

Mixing O2 with gasoline at the molecular level matters... even with all that other N2 and CO2 that try to get in the way...

 

We kind of get a coarse spray from our fuel injectors...  

where our fuel doesn’t get warmed very much...

Any benefit to changing the tried and true standard of today? Finer spray?

Heating the mixture may provide a more uniform mixture for better burning...

But, would make it more difficult to stuff more into an NA engine...

 

PP thinking out loud only...

Best regards,

-a-

Fuel is easy, meaning additional fuel is easy, even if you heated it or even if for some reason you were to vaporize it first.

‘However higher intake charge density is desired, drag racers will run their fuel through a can with ice in it trying to gain a tiny bit of charge cooling, the heat absorbed by evaporating fiel isn’t trivial, the intake of an alcohol fuel motor can feel ice cold for instance and that cold of course helps with charge density.

‘So in other words heating fuel while sometimes is done, it’s usually done to prevent icing etc., like a turbine for example will often have fuel heaters, but it’s not done to increase efficiency or power etc.

‘The GE T-700 has a neat design, its fuel heater, is the engines oil cooler, so you get both in one device.

 

On edit, we are not direct injection or timed injection, we have a continuous spray of fuel shot at the backside of the intake valve, what that means is that  all of the fuel or almost all anyway has vaporized prior to being sucked into the engine, and the tiny bit that’s not will be before combustion.

‘Droplet size, spray pattern etc is far more important in a turbine or a Direct injection Diesel.

Edited by A64Pilot
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2 hours ago, A64Pilot said:

I disagree with the plus or minus 5 degrees of timing won’t make much difference, it will make big differences, increasing timing will certainly increase power, but your reducing your margin for detonation.

Sorry for the confusion. I did not mean to imply that changing timing does not affect detonation margin. I only meant that small offsets from MBT timing don't have much effect on torque. Here's a graphic taken from Amann, C.A.: "Cylinder Pressure Measurement and it's Use in Engine Research." SAE paper 852067, 1985.

IMG_3944.jpg.ba5f9ac07fae22e5f4b3132b6a1a69ae.jpg

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Here is a report done by the NACA in 1940 showing the effects of mixture and ignition timing on engine performance including measured cylinder pressure, temperature IMEP (torque), and BSFC. It shows several interesting things:

1. There is a lot of cycle-to-cycle variation in the peak pressure location especially as mixtures move farther (rich or lean) from stoichiometric.

2. The cylinder pressure vs crank angle curves are very similar for very rich and very lean mixtures indicating that the primary effect is slowing of combustion in either case.

3. Lean mixtures reduce the magnitude and position of the peak pressure and this can be corrected by resetting ignition timing earlier which results in improvement in IMEP (increase) and BSFC (decrease). It should also increase CHT, but this was not plotted. Very rich mixtures also were not plotted, but would presumably have a similar characteristic.

4. As predicted by dissociation analysis, maximum cylinder head temperature occurs at a mixture which is slightly rich of stoichiometric yet leaner than the mixture for maximum peak pressure and maximum torque occurs at the mixture for maximum peak pressure.

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NACA-TN-772.pdf

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33 minutes ago, PT20J said:

Sorry for the confusion. I did not mean to imply that changing timing does not affect detonation margin. I only meant that small offsets from MBT timing don't have much effect on torque. Here's a graphic taken from Amann, C.A.: "Cylinder Pressure Measurement and it's Use in Engine Research." SAE paper 852067, 1985.

IMG_3944.jpg.ba5f9ac07fae22e5f4b3132b6a1a69ae.jpg

I would answer by saying look at the difference between 20 and 30 degrees advance to see how large that is.

As a kid I built and raced drag racing motorcycles for Star Cycle in Americus Ga., I’ve put many an engine on a dyno and “played” with timing, it’s pretty universally accepted that timing advance can make a large difference in power output, and can really get you into detonation quickly and a blown motor, I mean in a hurry.

‘For turbo motors it was pretty common to have a boost retard, that is as boost built, timing was backed off, also alcohol / water injection.

‘Now aircraft won’t have a boost retard, as it’s a complication that’s not needed, because you can’t bog down an airplane the prop just slips, but a wheeled vehicle you can get pretty high boost at lower RPM.

‘Pretty sure alcohol / water injection was common in WWII to help prevent detonation from high boost.

The people abdicating to advance your timing from 22 to 25 degrees really are seeing a significant increase in power, but they are also operating at a reduced detonation margin.

‘TANSTAAFL 

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I said small changes.

I don't believe anyone is advocating changing timing in an unapproved manner. Lycoming IO-360s are approved for either 20 or 25 deg BTDC. About 45 years ago, Lycoming made 20 deg standard on all but the dual mag engines (because the Bendix dual mag was not available with an appropriate lag angle for starting). There is continued debate about whether the difference means that the engines put out less power. Lycoming says they still meet spec. There is anecdotal evidence that they put out less power at 20 degrees and some have set them to 25 which is approved by the TCDS. I would really like to see some dynamometer data, comparing the two timings on the same engine.

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Bumping 5 degrees will increase torque I’m sure, the exception to that would only be say in a low compression motor running high enough octane fuel where detonation just isn’t possible and their timing was set for max torque, if that were the case then any change would be a reduction of torque

Maybe you couldn’t detonate an R-1340 or a C-85 on 100LL as they were both certified for 73 min octane fuel.

I’m not going to try though

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1 hour ago, PT20J said:

I said small changes.

I don't believe anyone is advocating changing timing in an unapproved manner. Lycoming IO-360s are approved for either 20 or 25 deg BTDC. About 45 years ago, Lycoming made 20 deg standard on all but the dual mag engines (because the Bendix dual mag was not available with an appropriate lag angle for starting). There is continued debate about whether the difference means that the engines put out less power. Lycoming says they still meet spec. There is anecdotal evidence that they put out less power at 20 degrees and some have set them to 25 which is approved by the TCDS. I would really like to see some dynamometer data, comparing the two timings on the same engine.

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On automobiles the timing advance map depends on a number of inputs, including rpm, either atmospheric pressure or MAF, fuel pressure, etc.   Picking one timing setting is only optimal for one set of conditions and a compromise for everything else, so checking the differences between 20 and 25 will either be multivariate or have to be done under controlled circumstances to really tell the difference.

As you point out, though, the typical operating conditions for GA engines allow for some slop across the compromise space, so it really might not make too much difference.

People often point out that there is no tolerance specified on timing, e.g., it's 25 degrees, period.   Not +/- 1.0 degrees, or whatever, so therefore it must be set very accurately.   Or so they say.   There's always adjustment tolerance, and the 25-or-20 suggests there's actually quite a bit of tolerance.   

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19 hours ago, PT20J said:

I run my engine pretty much the same as you do. If I'm low and just fooling around and not in a hurry to get anywhere, I'll run it LOP. But I live in the Pacific NW where it's hard to go anywhere without climbing over a mountain. So when I'm traveling, I usually run peak for best tradeoff (for me) of speed and efficiency. At peak EGT fuel flow, my 64 gallon tanks will last longer than I care to sit in a little airplane in one stretch and I figure I pre-saved on fuel by not buying a big-engined airplane, so I don't really need the extra economy of LOP.

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A little thread hijack, but I noticed when I was doing some whale watching this weekend on the coast (never found any, though), I was puttering along around 115 KIAS, and I smugly pointed out that was the maximum cruise speed of the Archer she'd been taking lessons in.  My wife asked how long we could look spend looking for whales before running out of fuel.  At 5.5 gph and 50 gallons left, I told her about 9 hours.  She decided she was okay heading home at that point.

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14 hours ago, carusoam said:

Any benefit to changing the tried and true standard of today? Finer spray?

Heating the mixture may provide a more uniform mixture for better burning...

But, would make it more difficult to stuff more into an NA engine...

 

I imagine those WWII carbureted turbocharged engines had some pretty good air/fuel mixing :)  I imagine few things atomize fuel as well as a blender turning at a couple hundred thousand RPMs!

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1 hour ago, A64Pilot said:

I would answer by saying look at the difference between 20 and 30 degrees advance to see how large that is.

FWIW, that's not a linear scale.  There's only a 5% loss of torque between 20 and 30 degrees

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1 hour ago, PT20J said:

I don't believe anyone is advocating changing timing in an unapproved manner. Lycoming IO-360s are approved for either 20 or 25 deg BTDC.

Ha!  I recall in one of Mike Busch's webinars, he did, in fact, bemoan the fact that you couldn't set the IO-360 to 22.5 degrees or something in between... Of course, I don't think he actually advocated doing so

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Looks like another turbonormalized Bonanza had a similar event. 

https://www.beechtalk.com/forums/viewtopic.php?f=37&t=193827

Edit:  I did a search on BT and found this older one mentioned in the thread above:

https://www.beechtalk.com/forums/viewtopic.php?f=37&t=106789

So here are three preignition events, all turbonormalized Bonanzas, all running LOP, at least one at at high power. So, perhaps I'm seeing the answer to my question about whether LOP cools the engine enough to allow cruising at high powers and low fuel flow. 

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A64,

You will see plenty of discussion of people changing ignition timing around here from 20 -25 BTDC...

This is an oddity in GA...  some Mooneys were born with 25° timing... and got changed to a more relaxed 20° timing...

If you are knowledgable, and have an engine monitor...the availability of going back to 25° is an acceptable legal maneuver... when done properly...

I think you may be under the impression, people have taken it on themselves to make the change because they feel like it...

You have referenced hangar elves before... 

I’m pretty sure we haven’t gone completely experimental around here here...

For references between 20 and 25°... that would be continental engines that use 22 as their standard...

It really helps when you get to know all 3k MSers...

We get several new MSers each week...  And every now and then they arrive asking questions similar to experimental planes...

There are good times to mention we are not in the experimental category...

There are times when your efforts are better used fighting the good fight... 

It takes a while to get to know all the players... and how they write... and what they meant...

You can always ask... PMs work really well...

Best regards,

-a-

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