Bad mpg?

[Antonm]

This is because a 6.2 filled to a 14.7 afr (for example) will make more power than a 5.3 L engine filled up at 14.7 afr.

Is this a statement you are willing to stand behind? Its totally wrong, but that hasn't stopped you before.

If you put 10cc of fuel (or really any given amount of fuel within the range each engine can efficiently burn) in either engine (part throttle stuff where talking here) and mix in air to the same AFR, then guess what,,,,, both engines will be making the same power.

The only slight difference would be any difference in efficiency between the engines (which a 5.3 and 6.2 having the same design, they have pretty similar efficiencies).

So that statement ,yet again, demonstrates a gross conceptual error in your part.

And now you go blathering on about transmission downshifts and other crap. The facts are a 5.3 and 6.2 will get very similar (talking second significant digit differences) in fuel milage if driven under the same conditions, moving the same mass. Even the stupid EPA fuel milage test they put on the window sticker shows this.
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[blanchard7684]

Is this a statement you are willing to stand behind? Its totally wrong, but that hasn't stopped you before.

If you put 10cc of fuel (or really any given amount of fuel within the range each engine can efficiently burn) in either engine (part throttle stuff where talking here) and mix in air to the same AFR, then guess what,,,,, both engines will be making the same power.

The only slight difference would be any difference in efficiency between the engines (which a 5.3 and 6.2 having the same design, they have pretty similar efficiencies).

So that statement ,yet again, demonstrates a gross conceptual error in your part.

And now you get blathering on about transmission downshifts and other crap. The facts are a 5.3 and 6.2 will get very similar (talking second significant digit differences) in fuel milage if driven under the same conditions, moving the same mass. Even the stupid EPA fuel milage test they put on the window sticker shows this.
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See previous posts and the linked material. There is an equation for power that literally shows the relationship I’m referencing.

 

[Antonm]

https://view.officeapps.live.com/op/view.aspx?src=https%3A%2F%2Fwww.webpages.uidaho.edu%2Fmindworks%2FIC_Engines%2FLectures%2FLecture%252007%2520-%2520Relationships%2520Between%2520Parameters.pptx&wdOrigin=BROWSELINK

See equation on slide 4.

nv is VE, Vbdc is engine displacement, AFR is air/fuel ratio.

For the power required to execute part load manuever, it is same because it is essentially the same mass.

The difference is engine displacement. The argument at hand is if the 6.2 can do this at higher AFR vs 5.3.

Based on that equation, if you assume VE is constant, the 6.2 can have higher AFR and make same power because the Vbdc term is increased.

So moving the mass up an incline, or into headwind, or tip in acceleration, for instance, the 6.2 can reach the required P on lhs of equation at higher AFR than 5.3 assuming throttle position is constant.

But, if 5.3 increases Ve via throttle, it can reach the required power. However throttle position and AFR are linked together inversely. So the 5.3 has to move to a lower BSFC area on its BMEP vs BSFC curve. This is in rel world represented by the fuel tables and shift schedule.

So the smaller engine will have a harder time keeping fuel consumption minimized in part-load conditions.

This is my point.

OMG are you a moron. Throttle position alone does not, repeat not, decide what the AFR is all by itself, the PCM and its ability to change the amount of fuel delivered gets a vote too in what the afr is .

You can have the same afr at just about any throttle position if the tuner decides that's what they what. And the factory calibrations have it as lean as they can safely get away with for CAFE standard / catalytic reasons.

Yeah during tip -in throttle they PCM commands more fuel, otherwise the engine would bog (basically the PCM is performing the same function as a carburetor accelerator pump did back in the olden days), but the OEMs want that AFR back to as lean as they can get it, as quickly as they can get it, for those all important fuel mileage and catalytic converter longevity reasons, so it doesn't stay rich for long.

And BTW, your link doesn't work.



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[Antonm]

See previous posts and the linked material. There is an equation for power that literally shows the relationship I’m referencing.

Could you post a copy or screenshot of this equation? That way I can show you how you're mis-interpreting it , well, assuming even applies at all that is.
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[blanchard7684]

OMG are you a moron. Throttle position alone does not, repeat not, decide what the AFR is all by itself, the PCM and its ability to change the amount of fuel delivered gets vote too in what the afr is .

You can have the same afr at just about any throttle position if the tuner decides that what they what. And the factory calibrations have it as lean as they can safely get away with for CAFE standard reason.

Yeah during tip -in throttle they PCM commands more fuel, otherwise the engine would bog (basically the PCM is performing the same function as a carburetor accelerator pump did back in the olden days), but the OEMs want that AFR back to as lean as they can get it, as quickly as they can get it, for those all important fuel mileage and catalytic converter longevity reasons, so it doesn't stay rich for long.

And BTW, your link doesn't work.

View attachment 447596

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OMG are you a moron. Throttle position alone does not, repeat not, decide what the AFR is all by itself, the PCM and its ability to change the amount of fuel delivered gets vote too in what the afr is .

You can have the same afr at just about any throttle position if the tuner decides that what they what. And the factory calibrations have it as lean as they can safely get away with for CAFE standard reason.

Yeah during tip -in throttle they PCM commands more fuel, otherwise the engine would bog (basically the PCM is performing the same function as a carburetor accelerator pump did back in the olden days), but the OEMs want that AFR back to as lean as they can get it, as quickly as they can get it, for those all important fuel mileage and catalytic converter longevity reasons, so it doesn't stay rich for long.

And BTW, your link doesn't work.

View attachment 447596

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Link fixed.

Let me summarize.

Power = efficiency factors x Heating value of fuel x VE x displacement x rpm/(afr x constants).

So a 5.3 makes less power than a 6.2 at the same afr.

slide 4.

This is a rearranged formula from Heywood text on combustion engines.

 

[blanchard7684]

OMG are you a moron. Throttle position alone does not, repeat not, decide what the AFR is all by itself, the PCM and its ability to change the amount of fuel delivered gets vote too in what the afr is .

You can have the same afr at just about any throttle position if the tuner decides that what they what. And the factory calibrations have it as lean as they can safely get away with for CAFE standard reason.

Yeah during tip -in throttle they PCM commands more fuel, otherwise the engine would bog (basically the PCM is performing the same function as a carburetor accelerator pump did back in the olden days), but the OEMs want that AFR back to as lean as they can get it, as quickly as they can get it, for those all important fuel mileage and catalytic converter longevity reasons, so it doesn't stay rich for long.



...

OMG are you a moron. Throttle position alone does not, repeat not, decide what the AFR is all by itself, the PCM and its ability to change the amount of fuel delivered gets a vote too in what the afr is .

You can have the same afr at just about any throttle position if the tuner decides that's what they what. And the factory calibrations have it as lean as they can safely get away with for CAFE standard / catalytic reasons.

Yeah during tip -in throttle they PCM commands more fuel, otherwise the engine would bog (basically the PCM is performing the same function as a carburetor accelerator pump did back in the olden days), but the OEMs want that AFR back to as lean as they can get it, as quickly as they can get it, for those all important fuel mileage and catalytic converter longevity reasons, so it doesn't stay rich for long.

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No where in this post does it even remotely suggest throttle position is the only input for injector output.

MAF, engine speed, pedal position, cyl head temp, 02 readings, etc etc...all are inputs.

The engine is trying to reach a power output that is commanded, not an afr.

I'm sure you know enough to know that you can't just have any afr at any engine load or any engine speed. The limitations of knock or fuel vaporization apply.

Again the "tuner" is trying to make the engine reach a certain torque level.

 

[blanchard7684]

Is this a statement you are willing to stand behind? Its totally wrong, but that hasn't stopped you before.

If you put 10cc of fuel (or really any given amount of fuel within the range each engine can efficiently burn) in either engine (part throttle stuff where talking here) and mix in air to the same AFR, then guess what,,,,, both engines will be making the same power.
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What burns or combusts is the mixture. one engine has a smaller amount of the mixture than the other.

 

[B-train]

Ok since I’m so clueless you tell me:

How is it the 6.2 can get nearly identical mileage as the 5.3 in the same suv with same gear and same mass?

Since your knowledge is so vast and impressive it should be easy.

I have offered a plausible explanation with facts and solid theoretical basis.

Your turn…

I would say that a 6.2L can get the same MPG because it's not working as hard to move the same mass. It's also true for the old 8.1L in the 2500 avalanche. I know of people who got almost 20 mpg cruising steady on road trips because the motor could just loaf along and didn't need extra fuel to keep up with the load. There are all kinds of variables obviously, but when you compare torque maps the higher torque will always win.

I've had 6.2L denalis for 15 years now and I will say that they get the same, and sometimes better, than the 5.3L yukon I used to own prior to that. Yes, they are the newer generation, but the power output when fed the right fuel is phenomenal. Training the right foot is key.....

 

[Antonm]

Link fixed.

Let me summarize.

Power = efficiency factors x Heating value of fuel x VE x displacement x rpm/(afr x constants).

So a 5.3 makes less power than a 6.2 at the same afr.

slide 4.

This is a rearranged formula from Heywood text on combustion engines.

I think maybe when you fixed the link you directed it to the wrong paper. Because nowhere in the paper you linked (the paper done by the EPA titled "Characterizing Factors Influencing SI Engine Transient Fuel Consumption for Vehicle Simulation in ALPHA"), does it ever even mention the term air-fuel ratio in it,,, anywhere , not even ctrl+f could find that term in the downloaded pdf, so its not like I skimmed over it.

Here's a copy past of the slide 4

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[blanchard7684]

I think maybe when you fixed the link you directed it to the wrong paper. Because nowhere in the paper you linked (the paper done by the EPA titled "Characterizing Factors Influencing SI Engine Transient Fuel Consumption for Vehicle Simulation in ALPHA"), does it ever even mention the term air-fuel ratio in it,,, anywhere , not even ctrl+f could find that term in the downloaded pdf, so its not like I skimmed over it.

Here's a copy past of the slide 4
View attachment 447605
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This link below is what I was referencing. slide 4.

https://view.officeapps.live.com/op/view.aspx?src=https%3A%2F%2Fwww.webpages.uidaho.edu%2Fmindworks%2FIC_Engines%2FLectures%2FLecture%252007%2520-%2520Relationships%2520Between%2520Parameters.pptx&wdOrigin=BROWSELINK

One of the many links I've provided.