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Okay, so for MPG, I figure its all about maximizing speed and minimizing RPMs.

On the street, 38 mph seems to hook into a gear and get you down to around 1500rpm, giving upper 30s for MPG.

For highway, I did the same and saw that at 55mph the car hooks into a lower RPM of 2000, so I thought that would be a good MPG setting, although kinda pisses everyone off around me.

However, here's the math.

55mph at 2000rpm

Multiply by 1.25 and you get 68.75mph at 2500rpm (55*1.25 @ 2000*1.25)... and guess what? The Focus goes at least 68.75 at 2500rpm. So, same MPG as at 55.

Multiply original by 1.5 and you get 82.5 at 3000rpm... and guess what again? The Focus goes at least 82.5 at 3000rpm.

Conclusion: MPG at 55, 70, 80.... all the same. Transmission not losing projected mph at higher RPMs... at least up to 82.5.

Agree?
 

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You forget to factor in wind resistance, tire rolling resistance, terrain, road conditions, tire pressure, etc. All will affect your MPG. It's not all about the mph and rpm.
 

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The problem is the assumption that the same amount of gas goes into the cylinder with each revolution of the engine. Rather, the speed of an engine is controlled by how much gas goes into the cylinder (position of gas pedal)--for a given rate of fuel injection, the engine will speed up or slow down depending on the resistance. So, with higher resistances (such as high speeds, climbing, wind, rough road, etc.) engine speed will decrease for a given rate of fuel injection, thus mpg will go down.
 

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Wind resistance is a cubic function (x^3) and above 55mph is the dominating factor in reducing fuel economy. So as a simplified example, the wind resistance felt at 55 is 166375 (55^3) at 75 it is 421875 (75^3). At 75mph is makes all other factors approach negligibility.
 

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Yeah.. practical stuff with the 2012 Focus it really does well up to near 50 mph or so.
The best mileage numbers i get are around 45mph with the peak number over an actual few miles being 48mpg on a flat road, no traffic.
((I think the pefect mileage max is around 35mph... the engine is at the minimum prm 1250 or so in fifth gear (manual) If I could actually drive at 35 on a freeway like road, 50mpg could be in sight.))
As soon as i am up over 50 mph the numbers drop a little.. and mileage drops more, the higher the speed over 50mph.
I think it could be better a little if the car had better gearing, or actually more overdrive gears suitable for getting the most from the engine at freeway speeds. but then it would be a seven speed manual gearbox, and an expensive one for a few mpg, and a lot more rowing around on the freeway.. (no cruise control use with a manual tranny,,)
 

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Nice attempt, but your logic is flawed here. As people have mentioned terrain wind resistance bla bla bla... all factor together to produce a load on the engine. The load has much more bearing on fuel delivery than RPM does. At WOT in gear at 3000 RPM the engine will be delivering far more fuel than at 6000 RPM in neutral. There are ways to use load to help develop more economical driving habits. You just need scanner that will read engine load. The Focus already has a feature that does this, however its just really dumbed down.
 

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Nice attempt, but your logic is flawed here. As people have mentioned terrain wind resistance bla bla bla... all factor together to produce a load on the engine. The load has much more bearing on fuel delivery than RPM does. At WOT in gear at 3000 RPM the engine will be delivering far more fuel than at 6000 RPM in neutral. There are ways to use load to help develop more economical driving habits. You just need scanner that will read engine load. The Focus already has a feature that does this, however its just really dumbed down.
If you leave your car in third gear, and drive at 65mph steady.
Or get into sixth gear, and drive at 65mph steady... I guarantee you will use a LOT more gas staying in third than staying in sixth!!
Just so, if the car had higher gearing to really maximize the load vs engine RPM etc. it could get better gas mileage than it does now at higher speeds. At issue is drivability, with a top gear that high, hills would cause the gearbox 9auto) to downshift. So again imo, one would want more gears in the top cruising range.
So an eight speed, with the top three gears just for over 50mph cruising...
Or in the manual tranny the top three for a seven speed transmission.

In driving around town, i find keeping the engine at MINIMUM rpms gives the best gas mileage in practice. 1,250 to 1,500rpms
So driving in fifth st 30mph (with the manual transmission) is the deal to keep the mpg over 37 in city driving.
And shifting before the tach hits 2,000rpm.
 

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If you leave your car in third gear, and drive at 65mph steady.
Or get into sixth gear, and drive at 65mph steady... I guarantee you will use a LOT more gas staying in third than staying in sixth!!
Just so, if the car had higher gearing to really maximize the load vs engine RPM etc. it could get better gas mileage than it does now at higher speeds. At issue is drivability, with a top gear that high, hills would cause the gearbox 9auto) to downshift. So again imo, one would want more gears in the top cruising range.
So an eight speed, with the top three gears just for over 50mph cruising...
Or in the manual tranny the top three for a seven speed transmission.

In driving around town, i find keeping the engine at MINIMUM rpms gives the best gas mileage in practice. 1,250 to 1,500rpms
So driving in fifth st 30mph (with the manual transmission) is the deal to keep the mpg over 37 in city driving.
And shifting before the tach hits 2,000rpm.
Clearly, your engine is doing more work than nessassaey to meet it's load targets! Im not about to type this up on my phone but I'm telling you that RPM has less to do with fuel economy than Load. I can type up a novel on how fuel delivery works if you want.
 

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Clearly, your engine is doing more work than nessassaey to meet it's load targets! Im not about to type this up on my phone but I'm telling you that RPM has less to do with fuel economy than Load. I can type up a novel on how fuel delivery works if you want.
Can you type up a novel when you get home? Because I'm pretty sure my fuel economy skyrockets going 35mph in 6th gear as opposed to 35mph in 5th gear. I could sure use a scangauge right about now...

But yes, load is still more important than anything.
 

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Can you type up a novel when you get home? Because I'm pretty sure my fuel economy skyrockets going 35mph in 6th gear as opposed to 35mph in 5th gear. I could sure use a scangauge right about now...

But yes, load is still more important than anything.
I don't recall saying that RPM doesn't factor in. All I said is load is the dominating factor.
 

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However, here's the math.

55mph at 2000rpm

Multiply by 1.25 and you get 68.75mph at 2500rpm (55*1.25 @ 2000*1.25)... and guess what? The Focus goes at least 68.75 at 2500rpm. So, same MPG as at 55.

Multiply original by 1.5 and you get 82.5 at 3000rpm... and guess what again? The Focus goes at least 82.5 at 3000rpm.

Conclusion: MPG at 55, 70, 80.... all the same. Transmission not losing projected mph at higher RPMs... at least up to 82.5.

Agree?
Experimentation over weekend indicates that with Hatch SEL AT:

2800 rpm = 77mph as noted on Garmin speed display.

Does this confirm on your chart?
 

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Clearly, your engine is doing more work than nessassaey to meet it's load targets! Im not about to type this up on my phone but I'm telling you that RPM has less to do with fuel economy than Load. I can type up a novel on how fuel delivery works if you want.
Theory is fine as long as it does not interfere with the real world.
I would argue a great deal on thoery, mainly the torque is what matters in real world driving, and the fuel needed vs the torque available at that load is what is important and that fuel is indeed used up twice as much at twice the rpm when carrying a minimal load, like cruising at a steady speed on level ground.
I can have the throttle barely cracked in fifth gear at 30 mph on level ground.
Yeah the moment i wanted to go up a hill i would be smarter to downshift than floor it, certainly. but for real world driving, lowest possible RPM with a light foot is the way to get max mpg.
 

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Theory is fine as long as it does not interfere with the real world.
I would argue a great deal on thoery, mainly the torque is what matters in real world driving, and the fuel needed vs the torque available at that load is what is important and that fuel is indeed used up twice as much at twice the rpm when carrying a minimal load, like cruising at a steady speed on level ground.
I can have the throttle barely cracked in fifth gear at 30 mph on level ground.
Yeah the moment i wanted to go up a hill i would be smarter to downshift than floor it, certainly. but for real world driving, lowest possible RPM with a light foot is the way to get max mpg.
An honest question, do you have any experience with engine management systems or tuning engines?
 

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Part of the load on an engine is its internal resistance. Engines have a maximum speed because the resistance of moving the cylinders, pumping losses, etc, eventually match the power output of the engine. These losses are generally quadratic. This is a factor why driving at low rpm yields better mpg.

Torque is a good measure of the fuel conversion efficiency of the engine, i.e., how much of the fuel energy gets turned into work. A perfect engine will have a flat torque curve meaning that at all engine speeds, the same amount of fuel energy turns into work. In reality, torque curves aren't totally flat. Depending on the torque curve & other factors, it may be possible to have worse mpg at very low rpm.
 

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Part of the load on an engine is its internal resistance. Engines have a maximum speed because the resistance of moving the cylinders, pumping losses, etc, eventually match the power output of the engine. These losses are generally quadratic. This is a factor why driving at low rpm yields better mpg.

Torque is a good measure of the fuel conversion efficiency of the engine, i.e., how much of the fuel energy gets turned into work. A perfect engine will have a flat torque curve meaning that at all engine speeds, the same amount of fuel energy turns into work. In reality, torque curves aren't totally flat. Depending on the torque curve & other factors, it may be possible to have worse mpg at very low rpm.
I've been looking for the RPM Torque Power Curve for this engine, I cannot find it anywhere. Do You have it ? We could then discuss this topic further.
 

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I've been looking for the RPM Torque Power Curve for this engine, I cannot find it anywhere. Do You have it ? We could then discuss this topic further.


Posted via FF Mobile
 

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Yeah, the engine is basically a limp sock before that [facepalm]
That and you don't want to put heavy loads at low RPM in High gears.
 

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A lot of dynos measure torque by how fast a weight can be accelerated and don't measure accurately at low RPMs. That's the primary reason a lot of dynos don't start recording data at low RPMs.

FWIW, HP = torque x rpm / 5250 that is the reason you always see the torque curve and HP curve intersecting at 5250 rpm.
 
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