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Highway speed gear 3.07 vs 2.87

Ronmar

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So, after reading the Eco Direct post…0.78x3.07x450 rev/mile = 1078 engine rpm at 60 mph in 7th…
It might get rolling decently using 1st all the time.
I think Caterpillar might not approve of running the vehicle up against air resistance max speed at that low rpm might be called lugging, although if allowed to the transmission would find a half decent gear. Maybe 5 or 6 depending on load.
Wouldn’t want to change hubs in the middle of a trip in a dirty environment.
Cheaper? Yes.
People who spend $120-170k on an Acela + many $100ks more on a fancy camper box wouldn’t go for it.
But it’s an interesting idea. It might, maybe, pull 7th with 3.9s empty.
3.04 final gearing. My Mog (similar weight and powerplant and air resistance and tires) has 4.36 final gearing in 8th.
Is the mog an automatic?

Remember this truck was not built for a commercial application. It was built to meet a MILSPEC. In the land of milspec, often serious compromises are acceptable, and often not even looked for/tested… A prime example of this on this same platform, is the grossly mismatched alternator to battery bank. Someone specced X amount of CCA but didn’t spec an appropriate amount of charging capacity to properly support it. The 2:1 hubs were probably chosen to help the package meet just such a specification. And unless you are only using the truck to perform those specified task(surmount an 18” curb at 26,000 pounds?), they may create compromises in other areas.
 

GeneralDisorder

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So, after reading the Eco Direct post…0.78x3.07x450 rev/mile = 1078 engine rpm at 60 mph in 7th…
It might get rolling decently using 1st all the time.
I think Caterpillar might not approve of running the vehicle up against air resistance max speed at that low rpm might be called lugging, although if allowed to the transmission would find a half decent gear. Maybe 5 or 6 depending on load.
It gets rolling essentially the same in 2nd because you now can fully load the torque converter.

You don't hit 7th till about 68+ MPH. Up to that point you are in 6th or 5th when it downshifts such as for passing (yes I frequently have to pass people now) or up grades.

The engine is very happy at 1400-1500 RPM. Runs MUCH cooler. > 3 mpg improvement.

Wouldn’t want to change hubs in the middle of a trip in a dirty environment.
Cheaper? Yes.
People who spend $120-170k on an Acela + many $100ks more on a fancy camper box wouldn’t go for it.
But it’s an interesting idea. It might, maybe, pull 7th with 3.9s empty.
3.04 final gearing. My Mog (similar weight and powerplant and air resistance and tires) has 4.36 final gearing in 8th.
I can pull well past 80 mph easily in 7th. So can my friend with a 2003 M1078 pulling his M1082 (8,500 lbs just in the trailer without a load).

Actually I will be helping a friend that has probably one of the nicest Acela overland builds switch over to direct drive hubs and possibly back to 3.90's. He's very excited for 370/931 on his C7 A1R. His habitat was built in Europe and he has far more invested than most. He's an engineer and immediately recognized the benefits.
 

Awesomeness

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Your not really dropping the 2:1, you are shifting it to the torque converter, which is so lightly used in these trucks typically because of the 2:1 in the hubs. IMO, Thats why the 2-3 shift happens so fast and so harsh(The lockup clutch was programmed to expect more load and slippage). With shifting the load into the TC, normal driving should be improved. Yes, you may not be able to muscle your way over an 18” curb anymore, but you also wont be roaring at max governed with high speed, high angle driveshafts anymore to try and flow with traffic….
You are literally dropping the 2:1... taking it out. So, (ignoring the unused 1st gear) it turns a closer-ratio 6-speed transmission into a wider-ratio 4-speed (across the same 0-65MPH driving speed range).

The fluid torque multiplication of the torque converter was there before, and is still there. You're not "transferring" anything to it, or activating it where it was inactive before. The truck just had lots of torque (e.g. for going over a 24" curb, which is the spec requirement), that wasn't frequently used, and now it has 1/2 as much (literally 1/2, because the 2:1 was removed).

None of this is likely to change fuel economy much. People always claim things improve MPG (e.g. aerodynamic kits, raising tire pressure, etc.), and there is a kernel of truth to all of it. What makes it a "kernel of truth" is that while it's possible to make tiny (0-5%) improvements, you can't beat the physics and get much more. This has been well studied across the entire automotive industry, including by the Army for these exact specific trucks (multiple times, one of which found that a 12% gain could be had by going to a 12-speed, not down in gears). Immediately, if someone (novice!) is claiming more than 5% gains, red flags should be going up.

The military studies (as well as all similar commercial truck studies) show very clearly that the most inefficient part of the whole system is the engine. It wastes 70% of the fuel, turning it into heat, meaning that ALL OTHER FACTORS COMBINED can do no more than affect the remaining 30% total. In other words, if you could make all other losses (e.g. wind resistance, transmission friction, tire rolling resistance, etc.) go away completely, the best you could do is improve fuel milage 30%. Ever. Period. Full Stop.
1684253265071.png

As a side effect of the 2:1 hub reduction removal, the drive shaft speed is cut in 1/2, which is good because these shafts operate close to max RPM. However, that means the drive shafts, u-joints, and axle shafts are taking 2x as much torque, which is definitely bad offroad.

Naming the hub change "Eco Hubs" is cute, but snake oil. The bottom line is that if somebody claims more than a 5% MPG change you should be suspicious. If they start talking 10-25%, you can be fairly certain they are wrong, without even looking at it. And the reason is physics... well understood, thoroughly studied, endlessly documented. But there is always some quack that is sure he's got the next big thing, if you just know the secret sauce he knows.
 

GeneralDisorder

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Those are just numbers in boxes - there's way too much left out to ascertain much of anything from that diagram. What were the test conditions (what speed for example?) and what assumptions were made due to "requirements" they were not allowed to change or even consider changing?

Real world testing suggests they overlooked, improperly calculated, or were mistaken about something - probably an assumption - that's often what trips up stuff like this. Or the "requirements" did not allow considering something.

Regardless - you're wrong or the study is wrong or both. I clocked 10.2 MPG and results speak for themselves - everyone else that installs these will see the same thing. Now it's up to the naysayers to eat crow and go back and find where their calculations went awry.

How many reports of 10+ MPG will it take for you to question this "study"? 10, 20, 50? It's going to happen and the market for 3.07's is going to tank. You might want to reconsider how hard you are claiming all of us are idiots and can't do some simple math with a gas pump receipt :shrugs:

Was this study done by the same guys that picked a 100a alternator? The Army is so fed up with that mess - all replacement engines (even the 3116) now come with 260's and all the bits and pieces needed to convert the truck.
 

Awesomeness

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Those are just numbers in boxes - there's way too much left out to ascertain much of anything from that diagram. What were the test conditions (what speed for example?) and what assumptions were made due to "requirements" they were not allowed to change or even consider changing?

Real world testing suggests they overlooked, improperly calculated, or were mistaken about something - probably an assumption - that's often what trips up stuff like this. Or the "requirements" did not allow considering something.

Regardless - you're wrong or the study is wrong or both. I clocked 10.2 MPG and results speak for themselves - everyone else that installs these will see the same thing. Now it's up to the naysayers to eat crow and go back and find where their calculations went awry.

How many reports of 10+ MPG will it take for you to question this "study"? 10, 20, 50? It's going to happen and the market for 3.07's is going to tank. You might want to reconsider how hard you are claiming all of us are idiots and can't do some simple math with a gas pump receipt :shrugs:

Was this study done by the same guys that picked a 100a alternator? The Army is so fed up with that mess - all replacement engines (even the 3116) now come with 260's and all the bits and pieces needed to convert the truck.
Best of luck to you. This is why my original statement was that there is no point arguing with such ignorance.
 

GeneralDisorder

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It's a discussion. I asked questions. You aren't providing any answers?

Lets just assume for a moment that I did actually get a 30% increase in fuel economy. I know you don't believe it - but as a thought experiment. Now work backwards from that assumption - how could it be possible? What would need to change for that to happen in your opinion? Perhaps we can either find out how it's possible or what assumptions I incorrectly made when performing my mileage test?

You will be faced with this question so you might as well consider it now - how is this increase possibly happening?
 
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fuzzytoaster

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Steering the conversation back on track here. I'm going to watch the ECO hubs closely to see the real world performance. There are some big claims made and I want to see them from non-affiliated sources not those directly manufacturing, distributing, profiting, etc off them. Solid 3rd party data with multiple points of data over a long duration is the only way for a true answer.

The data on the gear sets is solid. I've had both the 2.87 and 3.07 gears which perform flawlessly in my opinion. If the front chunk was easier to swap then I would be doing swaps every week. 3.07's in my A1R I could do 78 mph but it was not aerodynamic enough to sustain that. (Egads! A brick not being aerodynamic!)

I am curious to see how all this turns out in the long run for the hobby as these trucks were designed to meet military requirements and we are modifying them (again) to meet a different set of requirements. I do see a major issue with FMTVs running 70+ mph on stock tires rated for 55 mph regardless of method. Yes, yes under full load etc.. rated but that's not what a lawyer nor an officer will see. We may have solved a "want" for speed and created a "need" for safety. For the time being only operator training and testing can give us an answer.
 

Blairg

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During the research of installing the 2.87's I was curious to have heard more from the people who had talked about removing the reduction hubs. Unfortunately, at that time the Ecco hub wasn't around and installing the 2.87's seemed to be the only way of accomplishing a gear change with all the benefits of doing so. Certainly would have been less expensive and a simpler process of installation.
I will say that regardless of swapping the chunks out or installing the Ecco hub the truck becomes far more enjoyable over all.

Blair
 

GeneralDisorder

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Actually the speed rating of the current Goodyear MV/T is "K" which is 68 MPH.

PXL_20230511_204349269.jpg

Also I'm not affiliated or profiting from the ECO hubs other than my information being included for people looking to have their ECM reprogrammed.
 
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Lostchain

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The bottom line is that if somebody claims more than a 5% MPG change you should be suspicious.
With stock gearing, it essentially required 2800 RPM to hit 62mph. Deleting the reduction hubs basically halves that to do the same work. A 50% reduction in rpm manifests less than 5% better MPG in your mind? Any sceptic can test this immediately by simply driving their daily driver around in whatever gear it takes to be at redline all day long.. I think it's a self evident truth that they will impact their mileage by more than 5%
 
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Awesomeness

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With stock gearing, it essentially required 2800 RPM to hit 62mph. Deleting the reduction hubs basically halves that to do the same work. A 50% reduction in rpm manifests less than 5% better MPG in your mind?
Yes, because it isn't just a simple "cut everything in half" problem. Here's how it works:

If you are rolling down the highway at 62MPH, with the engine off/disconnected, you could add up all the resistances... aerodynamic drag, axle friction, tire rolling resistance, etc. Whatever that number is, we'll call it 100HP, is what you need the engine to produce to keep up that speed. It doesn't matter what gear your transmission is in, or what gearing is in your hubs, you need 100HP worth of energy to maintain 62MPH.

The engine needs a certain amount of fuel to generate 100HP. The need for 100HP output doesn't change, so your fuel economy isn't expected to change... MUCH.

Why "much"? Because the engine is more efficient at some RPMs (peak areas of the curve), and less efficient in other RPM ranges. These changes in efficiency aren't crazy - they are a single-digit percentage usually. (This is why you can see a general line-like trend to the engine's torque curve graph, before it gets to high RPM where it just can't pull air in any faster, physically.) So at 2600RPM the engine might need 10gal/hr of fuel to make 100HP, and at 1200RPM it needs 9.5gal/hr. That's a 5% change, not a 50% change, like you suggested.

Changing gearing, whether that be axles, hubs, or transmission, only changes the engine RPM needed to go a certain speed (e.g. 62MPH). If you expect to drive mostly at a certain speed (e.g. 62MPH on the highway, 90% of the time), you can try to optimize the gearing to put your engine RPM at the most efficient point. It's possibly in the middle of the curve, not just the lowest RPM possible, though you'd have to look at the graph for your engine specifically (or experiment to find out).

You need to take into account transmission shift points. What happens with the 3.07:1 axles gears is that while it helps make cruising at 65MPH be at like 2000RPM, around town where 45MPH and 55MPH are common the engine is at a high RPM but can't quite shift to the next gear. If you drive a wide variety of speeds, such as "around town, with some highway, and offroad", you can't target an ideal RPM with such a specific gear change.

One of the actual Cat 3116 HP/torque/fuel-consumption curves (look at the upper black lines, not the lower dashed ones):
1684267310905.png

General-purpose engines tend to have these straighter curves, because they need to do lots of different things "pretty well", and can't specialize in anything. When you get to specialized engines, such as high-performance race engines, the curve/peaks of the graph become more exaggerated. They are really good, really efficient in one narrow RPM range, and more terrible everywhere else.
 
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GeneralDisorder

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That fuel consumption graph appears (although it's a pretty terrible image) to show 1400 to 1600 RPM as 10 gallons per hour while 2600 RPM is approaching 15 gallons per hour. That's 50% more fuel so that would not contradict our ~30% increase in economy for cruising at 55 mph in 6th gear. Part of that time pulling grades and accelerating occurs at higher RPM against the torque converter so you wouldn't expect a perfect 50% savings.

Your own graph supports the ECO Hub results. :)
 

Awesomeness

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That fuel consumption graph appears (although it's a pretty terrible image) to show 1400 to 1600 RPM as 10 gallons per hour while 2600 RPM is approaching 15 gallons per hour. That's 50% more fuel so that would not contradict our ~30% increase in economy for cruising at 55 mph in 6th gear. Part of that time pulling grades and accelerating occurs at higher RPM against the torque converter so you wouldn't expect a perfect 50% savings.

Your own graph supports the ECO Hub results. :)
The graph is created on a dyno, at 100% engine utilization, which is why I took the time to explain it so carefully. Either you didn't read it, or couldn't understand it. Maybe you're just trolling, but I'm not sure if you deserve that much credit. If you need 100HP worth of fuel to go 62MPH, locked hubs won't change that.

These are complex topics, which is why no many people without in-depth knowledge can get excited about the perceived possibilities. All the time we hear claims about how there are new solar cars, underwater "gills" breathing devices, and perpetual motion machines getting ready to hit the market. But you can't get enough power from the roof of a car to make it go very far/fast, can't pull enough water through artificial gills to let a human breathe, and can't get more power out of a system than gets put in. It doesn't stop people from trying... over, and over, and over... and lots of naive people from buying into their schemes.
 

Lostchain

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So at 2600RPM the engine might need 10gal/hr of fuel to make 100HP, and at 1200RPM it needs 9.5gal/hr.

The whole discussion really centers around this particular bit of data. Would a legitimate test be to datalog the fuel consumption rate at a set speed before and after the hub change, with all other factors being equal ?
 

GeneralDisorder

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You keep trying to disprove the real world test results (which I assure you are real). I keep asking how I screwed up the test (and apparently everyone else that's done it) or how we can possibly explain the results of the test within whatever framework of reality you are prepared to accept. I'm still not getting any answers here. I'm willing to accept that I'm wrong but we need to hash out exactly what about my test caused the discrepancy of 3.3 MPG between two trucks running the same 118 mile course with the heavier, less aerodynamically efficient truck (in the lead mind you, not drafting something) being the one that improved it's economy by over 30%.......

And yeah I'm real familiar with dyno graphs and reading them. As much as you may think me a simpleton or an idiot - this idiot happens to own a $225,000 in-ground chassis dyno so...... yeah I do know a *bit* about them.
 

GeneralDisorder

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The whole discussion really centers around this particular bit of data. Would a legitimate test be to datalog the fuel consumption rate at a set speed before and after the hub change, with all other factors being equal ?
True - that data is available from the 3126 and C7 ECM. We could easily do this......
 

serpico760

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This may be a dumb question but I can't recall having seen this information. What is the stock gearing that fmtv A1 (3126) comes with? I had previously assumed that the 2.87 was the stock gearing.
 

Mullaney

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You keep trying to disprove the real world test results (which I assure you are real). I keep asking how I screwed up the test (and apparently everyone else that's done it) or how we can possibly explain the results of the test within whatever framework of reality you are prepared to accept. I'm still not getting any answers here. I'm willing to accept that I'm wrong but we need to hash out exactly what about my test caused the discrepancy of 3.3 MPG between two trucks running the same 118 mile course with the heavier, less aerodynamically efficient truck (in the lead mind you, not drafting something) being the one that improved it's economy by over 30%.......

And yeah I'm real familiar with dyno graphs and reading them. As much as you may think me a simpleton or an idiot - this idiot happens to own a $225,000 in-ground chassis dyno so...... yeah I do know a *bit* about them.
.
Wow!

With a dyno, you could take the aerodynamics out of the equation.
Then, two tanks of fuel - one with and one without the upgrade would tell a lot about the change...

I mean it wouldn't be a perfect test, but something could definitely be measured.
 
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