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Help me understand: UL94 fuel approval vs. compression ratio vs other aspects?


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Posted
On 2/14/2022 at 11:06 AM, A64Pilot said:

Yes, but they could do so more efficiently with a knock sensor. If you simply retarded timing based on MP or cyl head temp to a known safe advance, you would be unnecessarily reducing power, because you would have to reduce to a known safe timing for worse case, and of course lose a significant amount of power.

Toyota developed the knock sensor in 1980 I believe, it’s a pretty simple device really, it “listens” for detonation and as soon as it hears it, it retards timing until it goes away. I believe pretty much all cars since the early 90’s have it, I know my LT and LS engines do.

https://www.jstor.org/stable/44470940 Max power and also efficiency is produced right at the edge of detonation in a  normal engine.

This of course reduces power, and with aircraft, how do you develop charts etc when power is unknown?

Thing with water injection is you prevent detonation, without a loss of power. It most often used in fact in applications to increase power beyond the point you could without it. Water injection doesn’t change timing, just simply sprays a water mist into the suck side of the engine.

Everything comes with problems, like if the water injection and or knock sensor or reduction in timing didn’t happen for whatever reason, you would then be restricted in MP and I’m sure would need enunciation of failure.

Simplest answer is of course leave things where they are

IIRC, Knock sensors have been tested on aircraft but were not suitable to the noise environment. This was the reason George Braly developed PRISM (Pressure Reactive Intelligent Spark Management). It uses transducers on each cylinder to measure internal cylinder pressure and manages timing accordingly. Unfortunately, approval has been slow. Perhaps George has been too busy driving G100UL through the regulatory process.

Posted

You could get a knock sensor to work on an airplane. Issue is as I see it is a knock sensor in retarding timing, reduces power slightly, and regulatory wise that may be a tough approval.

Then there is the whole can you sell enough to make money on it as I’m sure it would pretty much have to be part of an electronic ignition package and look how that’s gone, then there is the actual truth that you would never save enough fuel to break even.

Lots of things could be done like an lightweight air cooled Diesel, but by the time development costs are spread over the tiny amount of sales, it becomes stupid expensive.

So we continue to fly behind our Grandfathers engines.

Think about it Porsche couldn’t make it work, even Toyota gave up, and I doubt Honda will ever break even on that Jet, and the biz jet market is extremely lucrative.

 

Posted
5 hours ago, Shadrach said:

IIRC, Knock sensors have been tested on aircraft but were not suitable to the noise environment. This was the reason George Braly developed PRISM (Pressure Reactive Intelligent Spark Management). It uses transducers on each cylinder to measure internal cylinder pressure and manages timing accordingly. Unfortunately, approval has been slow. Perhaps George has been too busy driving G100UL through the regulatory process.

Except that knock sensors have been used on the Lycoming iE2 Integrated Electronic Engine (YTEO-540-B1A) that has been installed in Lancair Evo's for more than 10 years .  (Lycoming announced the iE2 engine with acoustic knock sensors in 2008 - Textron Inc - Lycoming Engines Introduces the iE2 Integrated Electronic Engine Platform

Lancair: Evolution and Revolution - FLYING Magazine

Now it is being delivered this year on new Tecnam P2012 twin.  The only difference is that the Evo setup is single lever control while the Tecnam application (TEO-540-C1A) allows for full feathering prop control .  The iE2 engine has 6 knock sensors.

As Aviation Consumer said way back in 2010 the technology is merely evolutionary and that the early problems with acoustic knock sensors in aircraft engines were solved back before 2010.

"Acoustic knock detection has been a difficult nut to crack for air-cooled aircraft engines because their inherent vibration signatures make pinging difficult to extract from the hash of background noise. But knock sensors have gotten better and theres more processing horsepower available to separate the wheat of pinging from the chaff of banging valve trains and the whirr of gears. In any case, with individual cylinder knock detection, the IE2 suppresses detonation the same way it handles high CHTs-first with fueling, then with timing adjustments."

Lycoming IE2: Incremental Technology - Aviation Consumer

Lyco Manual 12 (lycoming.com)

Tecnam Aircraft's P2012 Traveller: 11 Seater Twin Engine Plane for Sale

image.thumb.png.b65ff9c567a48681756746c959bba1a4.png

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Posted
6 hours ago, 1980Mooney said:

Except that knock sensors have been used on the Lycoming iE2 Integrated Electronic Engine (YTEO-540-B1A) that has been installed in Lancair Evo's for more than 10 years .  (Lycoming announced the iE2 engine with acoustic knock sensors in 2008 - Textron Inc - Lycoming Engines Introduces the iE2 Integrated Electronic Engine Platform

Lancair: Evolution and Revolution - FLYING Magazine

Now it is being delivered this year on new Tecnam P2012 twin.  The only difference is that the Evo setup is single lever control while the Tecnam application (TEO-540-C1A) allows for full feathering prop control .  The iE2 engine has 6 knock sensors.

As Aviation Consumer said way back in 2010 the technology is merely evolutionary and that the early problems with acoustic knock sensors in aircraft engines were solved back before 2010.

"Acoustic knock detection has been a difficult nut to crack for air-cooled aircraft engines because their inherent vibration signatures make pinging difficult to extract from the hash of background noise. But knock sensors have gotten better and theres more processing horsepower available to separate the wheat of pinging from the chaff of banging valve trains and the whirr of gears. In any case, with individual cylinder knock detection, the IE2 suppresses detonation the same way it handles high CHTs-first with fueling, then with timing adjustments."

Lycoming IE2: Incremental Technology - Aviation Consumer

Lyco Manual 12 (lycoming.com)

Tecnam Aircraft's P2012 Traveller: 11 Seater Twin Engine Plane for Sale

image.thumb.png.b65ff9c567a48681756746c959bba1a4.png

Good to know. I still like the idea of using a combustion chamber pressure transducer to manage ignition. Seems like It would make for more sophisticated ignition tuning.

Posted
13 minutes ago, Shadrach said:

Good to know. I still like the idea of using a combustion chamber pressure transducer to manage ignition. Seems like It would make for more sophisticated ignition tuning.

I think you have a good point; direct measurement of the parameter vs reaction to an over limit condition.

However, I struggle with whether there really is a need for any kind of sophisticated electronic engine management system for what is a stationary engine. I've yet to see data that shows a payback in either fuel savings or appreciable power increase.

This whole E-mag/knock-sensor push seems to be a lot of solution looking for a problem.

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Posted
8 hours ago, MikeOH said:

I think you have a good point; direct measurement of the parameter vs reaction to an over limit condition.

However, I struggle with whether there really is a need for any kind of sophisticated electronic engine management system for what is a stationary engine. I've yet to see data that shows a payback in either fuel savings or appreciable power increase.

This whole E-mag/knock-sensor push seems to be a lot of solution looking for a problem.

Agree, I’ve said as much in e-mag threads. I had high hopes for additional power at cruise altitude but PIREPS from owners don’t suggest much gain. A lot of folks talk about improved starting, which is nice…except that I already find my plane easy to start.

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Posted
3 hours ago, Shadrach said:

Agree, I’ve said as much in e-mag threads. I had high hopes for additional power at cruise altitude but PIREPS from owners don’t suggest much gain. A lot of folks talk about improved starting, which is nice…except that I already find my plane easy to start.

+1.   It works on cars when there are additional sensors, like crank position, exhaust O2, anti-knock, mass air flow, etc., to manage spark timing.   Current emags don't get any of those inputs (except cam position), so don't have the means to do much useful regarding spark advance when compared to what is done on a typical automotive or computer-controlled engine management.   They're kinda stuck in 1950s vacuum-advance technology era at best, which isn't that great.

 

Posted
8 minutes ago, EricJ said:

+1.   It works on cars when there are additional sensors, like crank position, exhaust O2, anti-knock, mass air flow, etc., to manage spark timing.   Current emags don't get any of those inputs (except cam position), so don't have the means to do much useful regarding spark advance when compared to what is done on a typical automotive or computer-controlled engine management.   They're kinda stuck in 1950s vacuum-advance technology era at best, which isn't that great.

 

I wonder what base line mixture setting a company like SureFly uses for tuning.  Given the effect of mixture ratio on combustion speed it would be impossible to optimize a single timing map for multiple mixture settings without an O2 sensor. This is why I was so intrigued by Braly’s PRISM system. It seems that it dispenses with the need for measuring multiple parameters and optimizes ignition timing with just internal cylinder pressure (ICP) and crank angle. Moreover, it can adjust each cylinder’s timing independently which has the potential for extremely smooth operations at almost any viable mixture setting. 

Posted (edited)

The Stationary engine comment I’ve not heard before, but it’s actually spot on. Our cruise conditions, steady everything is pretty much how a stationary engine operates.

So it’s not tough to determine a timing lead that works under cruise conditions and just leave it set there, so your not at the peak of efficiency when your taxiing, who cares?

An automobile is different, it operates under widely varying conditions and even its fuel varies from time to time, so it makes sense that an automobile needs to be able to adjust to its widely variable RPM and load, but we don’t, we are essentially a stationary engine.

So you can show on paper how variable timing will be more efficient etc., but as we don’t fly paper airplanes in reality the increase in efficiency is so slight that it’s in the noise band, meaning it’s real, just so small it’s tough to measure. A couple % increase in efficiency over a fleet size of millions of automobiles is HUGE, but give me a couple % decrease in fuel consumption I don’t know if I’d notice it, and if it costs thousands of dollars I don’t think I’d ever break even.

In a very similar situation, I’d like to go Solar to get rid of my $300 a month electric bill, but I can’t make the numbers work, I mean Solar works of course, just at 14c a KWH and solar costing what it does, I won’t break even, ever.

Edited by A64Pilot
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Posted
2 hours ago, A64Pilot said:

The Stationary engine comment I’ve not heard before, but it’s actually spot on. Our cruise conditions, steady everything is pretty much how a stationary engine operates.

So it’s not tough to determine a timing lead that works under cruise conditions and just leave it set there, so your not at the peak of efficiency when your taxiing, who cares?

Do you understand the concept of efficiency ratios and how they effect combustion event speed? 
Piston speed (steady state or otherwise) is an important of the equation but it’s not the only part.

Posted (edited)

You and I have gone around and around with this, with your speaking about “Combustion Scientists” et all.

Yet here we are still, decades later with many people hawking fixes, advances etc. and yet there really hasn’t been an advance to amount to much, despite the claims.

When someone actually makes a significant advance, there will be a media splash to rival the announcement of Viagra and that’s not happened yet. I thought Porsche would be it, who else has more experience with modern high power air cooled engines than Porsche? 

But of course there are true believers, and that will never change. 

The over riding thread is that the manufactures of the engines are idiots, that they don’t know what they are doing, follow their recommendations at your peril, they are stuck back in the past etc. That (insert name here) is the true foundation of knowledge, they and not the manufacturers possess true knowledge.

The inconvenient truth is however that small increases in efficiency can be made, and have been made, but only by sacrificing something else, that Lycoming and Continental Engineers are not fools, nor do they think we are, despite the claims.

Most likely for their to be a significant improvement it will require significant hardware changes, four valve heads, Pentroof combustion chambers etc., the old two valve Hemi is well, old. Changes just like Automobiles and motorcycles have done, and Lycoming and Continental both have built geared motors, liquid cooled motors etc. and it keeps coming back to the fact that the simple direct drive air cooled opposed motor is tough to beat for its lightweight, simplistic design and ruggedness, expense etc.

As a mechanic I’ve always thought one of the stupidest designs was to put a pilot in charge of mixture, that even a simple mass air flow sensor with throttle position sensor would be better, because a pilot couldn’t hurt a motor that way, but apparently pilots do a decent job as only a few are damaged and the BSFC for an aircraft engine is actually pretty good, awfully good really

Think hard about why there has never been an actual good reliable auto engine conversion, that none have actually performed as well as a Lycoming or Continental, if there were the Experimental crowd would be flying them in droves.

Shockingly a Lycoming or Continental aircraft engine is actually pretty efficient, and is about the best you can get with the simple light weight design that it is.

Although the little Lycoming is pretty efficient, moreso than it’s big brother the big Conti’s actually have a BSFC that is as good or better than a modern automobile, discounting some outliers like Toyota’s Prius and one or two others.

 

Edited by A64Pilot
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Posted

^^^ What he said! ^^^
No matter how much the believers desire, there’s just not much improvement to be had. Whatever little there is just isn’t worth the cost in dollars and added complexity. And, I believe that added complexity decreases reliability rather than improves it!

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Posted
1 hour ago, A64Pilot said:

You and I have gone around and around with this, with your speaking about “Combustion Scientists” et all.

Yet here we are still, decades later with many people hawking fixes, advances etc. and yet there really hasn’t been an advance to amount to much, despite the claims.

When someone actually makes a significant advance, there will be a media splash to rival the announcement of Viagra and that’s not happened yet. I thought Porsche would be it, who else has more experience with modern high power air cooled engines than Porsche? 

But of course there are true believers, and that will never change. 

The over riding thread is that the manufactures of the engines are idiots, that they don’t know what they are doing, follow their recommendations at your peril, they are stuck back in the past etc. That (insert name here) is the true foundation of knowledge, they and not the manufacturers possess true knowledge.

The inconvenient truth is however that small increases in efficiency can be made, and have been made, but only by sacrificing something else, that Lycoming and Continental Engineers are not fools, nor do they think we are, despite the claims.

Most likely for their to be a significant improvement it will require significant hardware changes, four valve heads, Pentroof combustion chambers etc., the old two valve Hemi is well, old. Changes just like Automobiles and motorcycles have done, and Lycoming and Continental both have built geared motors, liquid cooled motors etc. and it keeps coming back to the fact that the simple direct drive air cooled opposed motor is tough to beat for its lightweight, simplistic design and ruggedness, expense etc.

As a mechanic I’ve always thought one of the stupidest designs was to put a pilot in charge of mixture, that even a simple mass air flow sensor with throttle position sensor would be better, because a pilot couldn’t hurt a motor that way, but apparently pilots do a decent job as only a few are damaged and the BSFC for an aircraft engine is actually pretty good, awfully good really

Think hard about why there has never been an actual good reliable auto engine conversion, that none have actually performed as well as a Lycoming or Continental, if there were the Experimental crowd would be flying them in droves.

Shockingly a Lycoming or Continental aircraft engine is actually pretty efficient, and is about the best you can get with the simple light weight design that it is.

Although the little Lycoming is pretty efficient, moreso than it’s big brother the big Conti’s actually have a BSFC that is as good or better than a modern automobile, discounting some outliers like Toyota’s Prius and one or two others.

 

That was along winded way of say  “no, I don’t understand efficiency ratio and it’s effect on  combustion speed…”

Posted (edited)
1 hour ago, Shadrach said:

That was along winded way of say  “no, I don’t understand efficiency ratio and it’s effect on  combustion speed…”

First I’m going to assume by efficiency ratio, your leaving out a word, do you mean volumetric efficiency ratio? Yes I understand it’s effect on flame spread as I do chemical superchargings effect as well as pulse and inertia tuning effect on volumetric efficiency

It’s really way more complex than that, there’s heat loss etc. The Brits were really very good with piston engines even back in the 1950’s, the Norton Manx achieved a volumetric efficiency of 125%, a number that still can’t be beaten even by the GP bikes and is considered to be a limit, but they did it 60 years ago, no one  has done better than the Brits did with that single cylinder 500cc motor, even with 21st centrury computer modeling etc.

But operating efficiency really does to a great extent come down to design, Modern GP bikes are hugely oversquare, that is the bore is much larger than the stroke to get big valves and improved breathing to make big power, but those big piston surface areas result in high heat loss so they give up efficiency while modern cars are usually slightly under square as that decreases heat loss and increases efficiency. So mission drives design and the rules really haven’t changed.

So to a great extent an engines efficiency or power output is based on design and is built in so to speak, sure you can increase power somewhat and can increase efficiency somewhat, but to get big gains you have to change design, rarely someone comes up with a totally new idea, like Toyota did with their Prius engine and via valve timing make it emulate an Atkinson cycle engine.  

So in other words there can be improvements made in efficiency of our engines by more effective management, but they are pretty small, a percent or two here and there, and that’s not insignificant but the BSFC of an engine is a function of design and more effective management can slightly improve it but it’s not going to be big improvements, largely due to our engines being basically stationary engines.

So to get big improvements in efficiency is going to take a new design, or some genius coming up with a different operating principle as Toyota did. 

However the problem with new designs is we have a weight limit and packaging requirements among other problems.

‘But progress is being made, That complicated intake plumbing on the big Conti’s now is I’m sure is inertia tuning and if Continental could build one exhaust system that would fit every aircraft then they could get into pulse tuning too both will  drive up volumetric efficiency

On edit Continental can’t of course build an one size fits all exhaust, and that’s one of the big problems, the airframe manufacturer build induction and exhaust and some do a much better job than others, and induction and exhaust have a rather large effect on volumetric efficiency, very large

Edited by A64Pilot
Posted

I suspect the PowerFlow exhaust is just better tuned than the stock ones. And, I think the stock F exhaust is pretty good; which is why the PowerFlow isn't as beneficial for it as it is on other models. 

Posted
19 minutes ago, A64Pilot said:

First I’m going to assume by efficiency ratio, your leaving out a word, do you mean volumetric efficiency ratio? Yes I understand it’s effect on flame spread as I do chemical superchargings effect as well as pulse and inertia tuning effect on volumetric efficiency

It’s really way more complex than that, there’s heat loss etc. The Brits were really very good with piston engines even back in the 1950’s, the Norton Manx achieved a volumetric efficiency of 125%, a number that still can’t be beaten even by the GP bikes and is considered to be a limit, but they did it 60 years ago, no one  has done better than the Brits did with that single cylinder 500cc motor, even with 21st centrury computer modeling etc.

But operating efficiency really does to a great extent come down to design, Modern GP bikes are hugely oversquare, that is the bore is much larger than the stroke to get big valves and improved breathing to make big power, but those big piston surface areas result in high heat loss so they give up efficiency while modern cars are usually slightly under square as that decreases heat loss and increases efficiency. So mission drives design and the rules really haven’t changed.

So to a great extent an engines efficiency or power output is based on design and is built in so to speak, sure you can increase power somewhat and can increase efficiency somewhat, but to get big gains you have to change design, rarely someone comes up with a totally new idea, like Toyota did with their Prius engine and via valve timing make it emulate an Atkinson cycle engine.  

So in other words there can be improvements made in efficiency of our engines by more effective management, but they are pretty small, a percent or two here and there, and that’s not insignificant but the BSFC of an engine is a function of design and more effective management can slightly improve it but it’s not going to be big improvements, largely due to our engines being basically stationary engines.

So to get big improvements in efficiency is going to take a new design, or some genius coming up with a different operating principle as Toyota did. 

However the problem with new designs is we have a weight limit and packaging requirements among other problems.

‘But progress is being made, That complicated intake plumbing on the big Conti’s now is I’m sure is inertia tuning and if Continental could build one exhaust system that would fit every aircraft then they could get into pulse tuning too both will  drive up volumetric efficiency

I don’t mean volumetric efficiency ratio.  I mean combustion efficiency ratio (air/fuel). Complete combustion in a gasoline engine occurs at 14.7:1 modern DFI auto engines run Air/fuel ratios (AFR) in excess of 30:1 when in steady state. Why do you think that might be? Do you think it would be possible with fixed ignition timing? Mixture has a significant effect on how much “bang” there is but also how fast said “bang” happens. Generating maximum Energy from a unit of fuel is not the same thing as converting that energy mechanical work. That energy must be transferred to the crank at the optimum time and duration.  Ignition controls the start of the event, mixture (and throttle) controls the amount and duration.

Back to Lycoming (or Continentals). As stated above, all other things being equal (ignition timing, air flow (MP), RPM setting etc…), mixture has a significant effect on how much “bang” there is and how fast said “bang” happens.  You cannot optimize ignition timing for both 100ROP and 40LOP. You can find reasonable compromise but you cannot optimize. This is why modern autos constantly monitor exhaust gases.
Would optimal vs compromised timing make a significant difference in aircraft cruise speed performance? Probably not much (Especially with a N/A engine) but maybe a little more noticeable at high DAs, perhaps a little more so in climb than cruise. What would likely be more noticeable is improvements in fuel economy.
 

My point regarding the new Emags is that they just don’t seem to have enough information to really optimize timing, at least not from the performance pireps that I’ve seen. 

Posted
58 minutes ago, Shadrach said:

I don’t mean volumetric efficiency ratio.  I mean combustion efficiency ratio (air/fuel). Complete combustion in a gasoline engine occurs at 14.7:1 modern DFI auto engines run Air/fuel ratios (AFR) in excess of 30:1 when in steady state. Why do you think that might be? Do you think it would be possible with fixed ignition timing? Mixture has a significant effect on how much “bang” there is but also how fast said “bang” happens. Generating maximum Energy from a unit of fuel is not the same thing as converting that energy mechanical work. That energy must be transferred to the crank at the optimum time and duration.  Ignition controls the start of the event, mixture (and throttle) controls the amount and duration.

Back to Lycoming (or Continentals). As stated above, all other things being equal (ignition timing, air flow (MP), RPM setting etc…), mixture has a significant effect on how much “bang” there is and how fast said “bang” happens.  You cannot optimize ignition timing for both 100ROP and 40LOP. You can find reasonable compromise but you cannot optimize. This is why modern autos constantly monitor exhaust gases.
Would optimal vs compromised timing make a significant difference in aircraft cruise speed performance? Probably not much (Especially with a N/A engine) but maybe a little more noticeable at high DAs, perhaps a little more so in climb than cruise. What would likely be more noticeable is improvements in fuel economy.
 

My point regarding the new Emags is that they just don’t seem to have enough information to really optimize timing, at least not from the performance pireps that I’ve seen. 

Running super lean mixtures works great in engines that typically run at 20% power or so (auto engines). If that technology was applied to our engines, we could get excellent fuel economy while doing slow flight. But, nobody cares how good our fuel efficiency is while doing slow flight. They want to fly faster! That requires extracting the most amount of power out of our fuel. They pretty much figured that out in the 30s and nothing has changed since.

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Posted
2 minutes ago, N201MKTurbo said:

Running super lean mixtures works great in engines that typically run at 20% power or so (auto engines). If that technology was applied to our engines, we could get excellent fuel economy while doing slow flight. But, nobody cares how good our fuel efficiency is while doing slow flight. They want to fly faster! That requires extracting the most amount of power out of our fuel. They pretty much figured that out in the 30s and nothing has changed since.

Not true. Modern cars use lean mixtures at steady power settings well beyond what you’ve mentioned.  

Posted
Just now, Shadrach said:

Not true. Modern cars use lean mixtures at steady power settings well beyond what you’ve mentioned.  

Of course they do. But if you throw all that at a 360 CU engine that is burning car gas and turning 2700 RPM, You are unlikely to get 200 HP out of it.

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Posted
Just now, N201MKTurbo said:

Of course they do. But if you throw all that at a 360 CU engine that is burning car gas and turning 2700 RPM, You are unlikely to get 200 HP out of it.

Never claimed it would. We’re simply talking about optimized timing for RPM, mixture and MP, something that is not available in aircraft right now.

Posted (edited)
1 hour ago, Shadrach said:

Never claimed it would. We’re simply talking about optimized timing for RPM, mixture and MP, something that is not available in aircraft right now.

But timing is already optimized for cruise power, well actually takeoff power. If we put all those fancy microcontrollers to the task, they would end up right where we are now.

Edited by N201MKTurbo
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Posted
59 minutes ago, N201MKTurbo said:

But timing is already optimized for cruise power, well actually takeoff power. If we put all those fancy microcontrollers to the task, they would end up right where we are now.

Which one is optimized? The 25° BDTC on my data plate or your 20° On yours? They’re not optimized for any one power/mixture setting, they’re optimized to be a compromise…

Have you done any engine ignition tuning on automotive applications? It’s perfectly reasonable for an older “vacuum advance” engine to be 35° By 2500rpm with full throttle and that’s on pump gas. If the car were being tracked in Denver, it would be acceptable to add more advance.

Ever notice how a Lyc 4cyl will smoothly run far leaner than you’d ever need down low but power drops off noticeably sooner and engine runs rough under the same setting at higher altitudes? Why do you think that is? Do you think the fuel distribution changes at altitude?  No, you know better. It runs rough because 25° is not enough advance for the slow, low power combustion event.  

Posted
7 hours ago, Shadrach said:

Which one is optimized? The 25° BDTC on my data plate or your 20° On yours? They’re not optimized for any one power/mixture setting, they’re optimized to be a compromise…

Have you done any engine ignition tuning on automotive applications? It’s perfectly reasonable for an older “vacuum advance” engine to be 35° By 2500rpm with full throttle and that’s on pump gas. If the car were being tracked in Denver, it would be acceptable to add more advance.

Ever notice how a Lyc 4cyl will smoothly run far leaner than you’d ever need down low but power drops off noticeably sooner and engine runs rough under the same setting at higher altitudes? Why do you think that is? Do you think the fuel distribution changes at altitude?  No, you know better. It runs rough because 25° is not enough advance for the slow, low power combustion event.  

Mine doesn’t change with altitude.

Posted
26 minutes ago, Shadrach said:

Not all of us are so fortunate…;)

But to your point, SureFly already advances the timing at reduced manifold pressures. Yet all we hear are things like "Well it might go a little faster". I just don't think a lot of electronic magic will do that much. From someone who designs electronic magic for a living.

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