Mpg

[cruiser54]

OOh. Post up where to get it!!

[HOrnbrod]

Autometer makes them. #15210 for single gauge, #15211 for dual gauges. Amazon, Jegs, Amazon, lots of places carry them.

 

 

 

[cruiser54]

Fit nicely on XJ and MJ?

[HOrnbrod]

It fits perfectly on MJ/XJ up to 1996; they are model specific. Not so perfectly on 97 and up XJs as the A-pillar plastic contour changed slightly. No personal experience with these models though.

[hitman72]

so i guess the real question is what are you guys getting for MPG, i have been averaging 20 on the highway and less city?

[gogmorgo]

 

 

2250 RPM, for any gear.

 

The most efficient engine speed is the torque peak.

Not true. There's an efficiency point that moves around depending on load and a few other variables. Usually it's significantly below peak torque. Best mpg I've ever had was cruising at around 1800 rpm. If I go much faster, my fuel economy makes a steep downward curve.

 

onlyinajeep726, where did you get that list and what exactly are the numbers? As in where do they come from / how were they determined?

For the engine, the torque peak RPM is absolutely the most efficient operating speed. Torque is mundanely defined as "horsepower per revolution." so the engine speed that produces the most power per revolution is the most efficient engine speed.

 

[...]sitic losses above that speed.

 

It's not that I don't believe your evidence, it's that I know your conclusion is flawed and I'm still uncertain how your evidence supports it.

 

Think of it this way. When you're accelerating, you have the gas pedal pushed down. When you hit your desired speed and want to stop accelerating, you have to lift off the gas pedal. The throttle closes, less air gets in, and to maintain a proper fuel/air mixture, fuel flow is also reduced. Suddenly you're using less fuel, and you didn't change your engine speed at all. You knew that already.

 

Torque, as you know, is dependent on engine speed, and remains constant so long as the engine speed does. Horsepower, on the other hand, is the rate at which the engine converts energy into motion. As you know, horsepower peaks don't occur at the same point as torque peaks. The amount of power an engine puts out is dependent on the amount of power consumed by the load, or in other words, power is the energy required to maintain a certain engine speed at a certain load. All the energy in the engine comes from fuel. More energy required means more fuel required. Torque is simply a rotational force, and really doesn't have much to do with how much energy is converted. If you have very little load on the engine, you consume very little fuel. If there's a big load on the engine, you use a lot of fuel. No matter where you're at in the rev range.

 

Torque, as I said, is a rotational force. It follows that peak torque is obviously the point where your engine is making the most force. If I'm walking, my muscles are applying less force than when I'm running, mostly because when I'm running I bend my knees a lot more which gives me better leverage. Actually, if I'm pushing against something I end up in a position very similar to when I'm running, because I can better apply torque that way. As I'm sure you know, walking takes substantially less energy than running, even though there's much lower torque. The point I'm making is that you can waste a lot of energy just trying to maintain a high level of torque. Yes, cars and people aren't quite the same, but the physics of force and energy don't change.

 

As far as this rule of max torque= max efficiency, several hundred years of physicists say otherwise, and it completely goes out the window with my experience.

My best fuel economy in my MJ was a there-and back trip along the exact same stretch of road (massive tailwind wasn't a factor), at around 1800 rpm (massive tailwind wasn't a factor) at roughly 55mph. I've made the exact same trip going different speeds, from 60 to 80 mph, and never managed within 20% of that one best. The next best fuel economy I've had was only about 7% down from best on different roads but running at the same speed.

Another, even more drastic example of the lack of correlation between peak torque and peak mpg's is in my dad's old 3.4 Impala with a 4-speed auto. He gets his best fuel economy around the 50-55 mph mark in overdrive. Something like 36mpg. Peak torque is around 4000rpm. Don't even try telling me he's anywhere close to that in overdrive at 50 when second gear is good for 90+mph (which I know from being a teenager).

 

I've seen you say peak mpg is at peak torque several times in the past, giving the same arguments, even down to the huge snow tires, yet I have still have trouble seeing how they support your conclusion. The larger tires are a nice lesson in gear ratios and drag, but don't have anything at all to do with your argument.

 

Now, I'm not saying that lower rpm always equates to better fuel economy (my dad is still perplexed at how I manage to get better fuel economy in his van than he does when I drive it harder than him) or that it's not possible for peak economy to occur at peak torque, but if it does, it's merely a happy coincidence.

The maximum fuel efficiency point is where the energy required to maintain engine speed at a constant load is at a minimum. As speed increases, energy requirements go up. As speed decreases below peak torque, torque goes down. If you plot the two on a graph, where the two lines meet is peak economy. At higher engine speeds, you're just wasting energy making it turn faster. At lower engine speeds, you're not making enough torque to generate enough power to keep going without adding more fuel. You knew torque came into it somewhere, right? Also, as load increases, the point moves upwards, towards peak torque (I honestly don't know if the max economy point can ever go higher than peak torque, but I don't think so.) Reduce load, and it goes back down again. It's not a fixed point, even on cars where it can be at peak torque.

 

While not entirely related, this also explains why it's more efficient to accelerate at peak torque, as hypermilers will tell you. When you accelerate, you load the engine, which pushes your peak economy point up towards peak torque. But once you hit cruising speed, you stop accelerating, remove the load from the engine, and the economy point goes back down.

[gogmorgo]

so i guess the real question is what are you guys getting for MPG, i have been averaging 20 on the highway and less city?

My running average is in my sig. Right now I'm not doing as well as I was back in September and October because winter.

 

91 4L HO, automatic, Mostly that's cityish, where I've been getting typically around 13 mpg. A couple times I dropped to 8 because I spent a bunch of time pushing through deep snow in low range and being very stuck. On the highway I usually do 16-17, best I've done ever is 19.3. All on the US gallon. All the gas I've run through her except the tank I got the day I bought her and a couple $20 bumps (those tanks discluded from total) is on fuelly.

[Lee21490]

so i guess the real question is what are you guys getting for MPG, i have been averaging 20 on the highway and less city?

 

I get about 13~ avg in town (most of my driving is going up a massive hill to work every morning)

And about 17~ with pure highway.

 

95 4.0 HO in a 86 manche.

[Lee21490]

Autometer Air/Fuel meter. better than a vacuum gauge for monitoring fuel consumption.

 

Did you buy the wideband O2 sensor? Or just tap into the stock?

 

Seems like a good idea, But $40 for the plastic pillar ; $200~ for a wideband sensor ; $50~ for a A/F gauge seems like a bit much to save just a few more mpg.

 

 

Meant to edit instead of double posting, My bad.

[Eagle]

so i guess the real question is what are you guys getting for MPG, i have been averaging 20 on the highway and less city?

'88 XJ, 4.0L 5-speed, stock gears and 225/75R15 tires I typically get around 19 in local driving and 20 to 22 highway.

 

'88 MJ, 4.0L 5-speed with 3.73 gears and 31x10.50-15 tires, about 17 in local driving and 19 MPG highway.

[Biotex]

Do you have to install a seperate bung for the O2 sensor?

[HOrnbrod]

 

Autometer Air/Fuel meter. better than a vacuum gauge for monitoring fuel consumption.

 

Did you buy the wideband O2 sensor? Or just tap into the stock?

 

Seems like a good idea, But $40 for the plastic pillar ; $200~ for a wideband sensor ; $50~ for a A/F gauge seems like a bit much to save just a few more mpg.

 

 

Meant to edit instead of double posting, My bad.

 

Agree, too expensive. I used a narrow band Autometer A/F gauge and just tapped into the existing O2 sensor output to the ECU. It tells me all I need to know.

[Lee21490]

Do you have to install a seperate bung for the O2 sensor?

 

For the wide band sensor, Yes.

 

 

 

 

Autometer Air/Fuel meter. better than a vacuum gauge for monitoring fuel consumption.

 

Did you buy the wideband O2 sensor? Or just tap into the stock?

 

Seems like a good idea, But $40 for the plastic pillar ; $200~ for a wideband sensor ; $50~ for a A/F gauge seems like a bit much to save just a few more mpg.

 

 

Meant to edit instead of double posting, My bad.

 

Agree, too expensive. I used a narrow band Autometer A/F gauge and just tapped into the existing O2 sensor output to the ECU. It tells me all I need to know.

 

From what i've read (Only spent like 30 minutes lol) Hooking it up to a narrow band sensor will just "Give you a light show" On the gauge. And show nothing usefull.

[HOrnbrod]

Don't believe everything you read, it's more than a light show. Granted the wide band A/F meter is more exact and easier to read, but at 4X the cost and requiring the extra O2 bung, the narrow band A/F meter does all I need. In addition to showing the open to closed loop transition, it's useful for monitoring lean and rich conditions. But you must know what you are looking at to interpret it correctly.

 

Quoted from Dino's Stroker site:

 

The lean range is 0.050v-0.249v (four red LED's), the stoich range is 0.250v-0.749v (ten yellow LED's), and the rich range is 0.750v-1.000v (six green LED's). At idle and light throttle cruise, the gauge should fluctuate across the stoich range. Under WOT acceleration, it should be two to three LED's inside the rich zone (0.80-0.85v), while under hard deceleration the gauge should show full lean or even go off the scale altogether.

 

Until I read this, I didn't know what I was looking at and didn't know the ideal (stoich) range during normal ops. It does work. .

[cruiser54]

Don't believe everything you read, it's more than a light show. Granted the wide band A/F meter is more exact and easier to read, but at 4X the cost and requiring the extra O2 bung, the narrow band A/F meter does all I need. In addition to slowing the open to closed loop transition, it's useful for monitoring lean and rich conditions. But you must know what you are looking at to interpret it correctly.

 

Quoted from Dino's Stroker site:

 

The lean range is 0.050v-0.249v (four red LED's), the stoich range is 0.250v-0.749v (ten yellow LED's), and the rich range is 0.750v-1.000v (six green LED's). At idle and light throttle cruise, the gauge should fluctuate across the stoich range. Under WOT acceleration, it should be two to three LED's inside the rich zone (0.80-0.85v), while under hard deceleration the gauge should show full lean or even go off the scale altogether.

 

Until I read this, I didn't know what I was looking at and didn't know the ideal (stoich) range during normal ops. It does work. .

That's all I had on my supercharged Miata. Kept me from leaning out and was plenty good enough.

[Lee21490]

Don't believe everything you read, it's more than a light show. Granted the wide band A/F meter is more exact and easier to read, but at 4X the cost and requiring the extra O2 bung, the narrow band A/F meter does all I need. In addition to slowing the open to closed loop transition, it's useful for monitoring lean and rich conditions. But you must know what you are looking at to interpret it correctly.

 

Quoted from Dino's Stroker site:

 

The lean range is 0.050v-0.249v (four red LED's), the stoich range is 0.250v-0.749v (ten yellow LED's), and the rich range is 0.750v-1.000v (six green LED's). At idle and light throttle cruise, the gauge should fluctuate across the stoich range. Under WOT acceleration, it should be two to three LED's inside the rich zone (0.80-0.85v), while under hard deceleration the gauge should show full lean or even go off the scale altogether.

 

Until I read this, I didn't know what I was looking at and didn't know the ideal (stoich) range during normal ops. It does work. .

 

Wasn't saying i completely believe it, Just wanted more info.

 

What do you mean by "Slowing the open to closed loop transition"

[HOrnbrod]

 

Don't believe everything you read, it's more than a light show. Granted the wide band A/F meter is more exact and easier to read, but at 4X the cost and requiring the extra O2 bung, the narrow band A/F meter does all I need. In addition to slowing the open to closed loop transition, it's useful for monitoring lean and rich conditions. But you must know what you are looking at to interpret it correctly.

 

Quoted from Dino's Stroker site:

 

The lean range is 0.050v-0.249v (four red LED's), the stoich range is 0.250v-0.749v (ten yellow LED's), and the rich range is 0.750v-1.000v (six green LED's). At idle and light throttle cruise, the gauge should fluctuate across the stoich range. Under WOT acceleration, it should be two to three LED's inside the rich zone (0.80-0.85v), while under hard deceleration the gauge should show full lean or even go off the scale altogether.

 

Until I read this, I didn't know what I was looking at and didn't know the ideal (stoich) range during normal ops. It does work. .

 

Wasn't saying i completely believe it, Just wanted more info.

 

What do you mean by "Slowing the open to closed loop transition"

 

Whoops - typo. Meant SHOWING the open to closed loop transition.  :thumbsup:

[AMCJeepMJ]

So, for those whom have rented U-haul trucks recently, you may have noticed they have a gauge for 'best economy'... is it just a vacuum gauge?

[HOrnbrod]

Yes, I noticed that when we moved my daughter after college. That's a vacuum gauge for sure. In the 70s and 80s many cars had econometers, even the AMC Matadors. Autometer even makes one today calling an Ecometer.   :ack:

 

[Blue88Comanche]

here is dads current MPG

 

My current running mpg is in my sig