Highway speed gear 3.07 vs 2.87

[GeneralDisorder]

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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.

While that would be FUN! and also probably terrifying! it's sadly impossible with my setup. The dyno rollers are only 6' 10" wide and if they were wide enough for the FMTV I'm not sure the structure of the dyno itself would support the weight of the chassis. It is an AWD dyno though so the thought crossed my mind..... it would have to be someone else's truck since my 1079 won't fit through the bay door either. And it would probably have to be backed in with the transmission in MODE and the front driveshaft removed which would also limit you to 5th gear...... sadly I don't think it's even feasible. It's a race car dyno - totally inadequate for that application.

 

[Awesomeness]

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 ?

It would certainly be a better.

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.

I believe you measured those results, and that you believe them, but you should have immediately known better (unless you just don't understand these topics well).

What's wrong with your test?

1. One single test
2. Mostly just highway, at one speed (could be good for one, and bad for the other)
3. Two different trucks
4. Two different styles of trucks
5. Two different engines, a decade apart in design
6. No data from the truck before the hub change
7. Results that should be suspicious because of their magnitude
8. Crude measurement (e.g. fuel, distance, etc.)
9. Cherry picking data (newer C7 truck got the good MPG, old 3126 got the poor MPG), or biasing toward favorable results

The key is really #1... one single test. Many of the rest of them go away over time if you have long term testing of even just one truck, and even better if it is across several trucks.

Put it on that dyno then, before and after a change! That would be a start.

 

[GeneralDisorder]

I know well what my truck got before the change. I drove it 2800 miles home when I bought it and stayed at 50 mph as much as possible. Fuel economy was right in line with what the 1078 got in our test. Maybe slightly worse with the 1079 box.

The 3126b and the C7 are basically the same engine with very similar specs in terms of fuel consumption, etc. The C7 would probably be called the 3126c or the 3136 or something if it weren't for Caterpillar changing their naming/marketing conventions. The military version of the C7 does not have any of the emissions stuff they started putting on the civilian engines toward the end of over the road production.

It's not just a single test. Others have clocked their mileage and got similar results.

As far as the load and the dyno graph with fuel consumption - the engine is operating at full load with the reductions to go 55-60 MPH. At 1450 RPM cruising it's probably closer to 80%.... But that wouldn't affect the numbers all that much. Indeed if there were no grades to climb and it was perfectly level for the whole test I would expect to be much closer to 50% increase in fuel economy.

 

[Awesomeness]

As far as the load and the dyno graph with fuel consumption - the engine is operating at full load with the reductions to go 55-60 MPH.

It's operating at full RPM, not maximum power output possible for the engine (at any RPM) or full load for that RPM. You just hit the governor and it stops accelerating.

It's making exactly as much power as necessary to maintain that speed, and that power requirement doesn't change because of gears. So the question becomes "How much fuel does it take to make 100HP at 1600RPM, versus how much fuel does it take to make 100HP at 2600RPM?", and the answer is that they are very close (in the neighborhood of 5%).

What does the dyno graph look like for an engine with a fuel starvation problem? It's a flat line across a certain HP. So just reverse that... same HP, same fuel.

 

[GeneralDisorder]

It's making exactly as much power as necessary to maintain that speed, and that power requirement doesn't change because of gears. So the question becomes "How much fuel does it take to make 100HP at 1600RPM, versus how much fuel does it take to make 100HP at 2600RPM?", and the answer is that they are very close (in the neighborhood of 5%).

You're forgetting drivetrain losses from turning everything in the drivetrain at double the speed. My front hubs used to get too hot to comfortably leave your hand on. Now they are cold. Its takes energy to create all that extra heat. And the faster you go the higher drivetrain losses get. So no it does not take the same amount of energy to maintain the same road speed at twice the RPM. The engine ABSOLUTELY must make more power to spin all that gear. Just the transmission fluid pump and transfer case scavenge pump have to turn twice as fast - both actually consume a fair amount of HP.

Just keeping the engine and all it's accessories spinning that fast requires more power - the oil pump, water pump, alternator, and cooling fan all REQUIRE HP. It is not going to be as simple as you describe. That's why real-world testing is valuable - if you only do this on paper you will probably miss something. That's why we have to build and test things like space rockets. The variables are very numerous and dynamic.

And the engine has to do all this - at an RPM that it is significantly less efficient at. Look at the graph - the peak torque is where the engine is most efficient. Not at 2600 RPM. So even producing less than peak power, it's efficiency isn't going to be as good at that RPM - so 100 HP at 1400 RPM is going to require less fuel than 100 HP at 2600 RPM.

 

[Awesomeness]

You're forgetting drivetrain losses from turning everything in the drivetrain at double the speed. My front hubs used to get too hot to comfortably leave your hand on. Now they are cold. Its takes energy to create all that extra heat. And the faster you go the higher drivetrain losses get. So no it does not take the same amount of energy to maintain the same road speed at twice the RPM. The engine ABSOLUTELY must make more power to spin all that gear. Just the transmission fluid pump and transfer case scavenge pump have to turn twice as fast - both actually consume a fair amount of HP.

Just keeping the engine and all it's accessories spinning that fast requires more power - the oil pump, water pump, alternator, and cooling fan all REQUIRE HP. It is not going to be as simple as you describe. That's why real-world testing is valuable - if you only do this on paper you will probably miss something. That's why we have to build and test things like space rockets. The variables are very numerous and dynamic.

And the engine has to do all this - at an RPM that it is significantly less efficient at. Look at the graph - the peak torque is where the engine is most efficient. Not at 2600 RPM. So even producing less than peak power, it's efficiency isn't going to be as good at that RPM - so 100 HP at 1400 RPM is going to require less fuel than 100 HP at 2600 RPM.

It's not as much as you are assuming. The only thing changing spinning here is the hub gears.

1HP=746W

So a 225HP engine is putting out 167,850W, and if 30% efficient is taking in 559,500W worth of fuel.

Now think about if you had a standard 1500W heat gun (a 2HP heat gun)... it would have that hub red hot in minutes.

So we're talking about a 1% change in energy from heating those hubs.

 

[GeneralDisorder]

1500w heat gun would probably never get those hubs much more than warmish. That's a lot of steel connected to a lot more steel. I think your sense of how much power it takes to get that much steel "red hot" is severely lacking. You would need an acetylene torch with a good sized rosebud and even then it would take longer than a couple minutes. I've done enough cutting, welding, and heating of large chunks of iron and shafting, etc in my career inside and outside of the Military to have a pretty solid sense of how much power it takes to heat up heavy pieces of casting.

That doesn't address the rest of the stuff that has to spin at twice the speed. When that cooling fan kicks in - bet you real world money that sucker takes 30+ HP to spin that fast.

 

[Awesomeness]

1500w heat gun would probably never get those hubs much more than warmish. That's a lot of steel connected to a lot more steel. I think your sense of how much power it takes to get that much steel "red hot" is severely lacking. You would need an acetylene torch with a good sized rosebud and even then it would take longer than a couple minutes. I've done enough cutting, welding, and heating of large chunks of iron and shafting, etc in my career inside and outside of the Military to have a pretty solid sense of how much power it takes to heat up heavy pieces of casting.

That doesn't address the rest of the stuff that has to spin at twice the speed. When that cooling fan kicks in - bet you real world money that sucker takes 30+ HP to spin that fast.

Ok, so by your expert opinion, 30+ HP, a full 10-13% of the engine HP is just spinning the hubs. Got it.

 

[GeneralDisorder]

Well I estimated that for the cooling fan which is not 100% duty cycle. I'm not sure on the hubs but 1500w isn't going to do it. Not and have them uncomfortably warm to the touch with freeway speed air flowing over them for cooling. It's gonna take a HELL of a lot more than that. And whatever that larger number is, it's x4.

 

[serpico760]

I just happened to find online this interesting article regarding an efficiency study for the fmtv with different transmissions I thought it would be very useful information.
FMTV Transmission Fuel Economy Study - Evaluation of AMT Performance Using ... http://gvsets.ndia-mich.org/documen...Using Experimental and Analytical Methods.pdf

 

[Awesomeness]

Well I estimated that for the cooling fan which is not 100% duty cycle. I'm not sure on the hubs but 1500w isn't going to do it. Not and have them uncomfortably warm to the touch with freeway speed air flowing over them for cooling. It's gonna take a HELL of a lot more than that. And whatever that larger number is, it's x4.

What do you estimate then?

I think you're agreeing less than 30HP, which would be 10% on your engine. So where does the other 20%+ fuel economy gain come from? Driveshaft yoke bearings on the axle, spinning 1/2 as fast?

If you start working through these, you see why 30%+ MPG gains are so astronomical, and suspect.

At best you can account for a percent or two here and there, and that adds up to single digit percentages. Then you look at all the studies and scientific knowledge, and see that they usually only talk about gaining a few percent MPG, from even non-trivial upgrades. Then you factor in that if it was easy as taking out the 2:1 hubs (or adding selectable hubs transfer case), the Army could have cut 30% off their fuel budget, then why didn't they think of it or do it?

Go read a few of the FMTV fuel economy studies. They're really interesting, and the Army considered some pretty extreme changes like hybrid drivetrains and stuff... and the best they could do was get into the teens (% change), while most things resulted in single-digit changes that would really only be noticeable in a fleet setting (1% change across thousands of trucks adds up to $$$).

(Also, the fan is in one of the Army's MPG studies. If I remember correctly it's 17000W=23HP.)

 

[GeneralDisorder]

So did the Army ever do any testing that you can find with the 2:1 hubs removed?

You illustrate my point - why didn't they do it? Was it because they "didn't think of it" or because it was off the table from the start due to "requirements" that only really apply to boundary conditions but must be applied to all vehicles in the family for the sake of uniformity?

I can absolutely see all the components in the drivetrain and engine accessories adding up to 20% and the other 10% being various factors including engine peak efficiency. The air compressor I would estimate likely requires +5 HP at double the speed for example - it's EVERYTHING before the hubs running at twice the speed.

IDK man - I've been wrenching all my life in and out of the military and you do get a sense for how much power it takes to drive various pumps, fans, transmissions, gear reductions, etc. Especially owning a DynoJet and seeing what stock vehicles put to the wheels and knowing what their advertised power numbers are from the manufacturer, etc. You just get a sense for these things - it's hard to explain if you haven't done it. Like how do you describe what torque feels like when tightening fasteners? You can't it has to be learned by experience and feeling it - every new mechanic or shade tree has sheared off a bunch of fasteners before he learns that feel.

I have no problem believing the results and I'm going to go enjoy my truck and it's reduced operating cost. The exact numbers of where all the gallons of additional fuel were spent and what they were driving isn't all that important to me. I'm convinced by the test data and the thickness of my wallet.

 

[Lostchain]

I just happened to find online this interesting article regarding an efficiency study for the fmtv with different transmissions I thought it would be very useful information.
FMTV Transmission Fuel Economy Study - Evaluation of AMT Performance Using ... http://gvsets.ndia-mich.org/documents/MSTV/2009/FMTV Transmission Fuel Economy Study - Evaluation of AMT Performance Using Experimental and Analytical Methods.pdf

That is an interesting study, they were able to gain 22% efficiency out of the FMTVs by testing other transmission and gear ratio combinations.

I my opinion, the most relevant part from their conclusions to this discussion: "The key enabler to the 22% improvement is the final drive ratio."

 

[Gunny 0369]

8679.56

 

[GeneralDisorder]

That is an interesting study, they were able to gain 22% efficiency out of the FMTVs by testing other transmission and gear ratio combinations.

I my opinion, the most relevant part from their conclusions to this discussion: "The key enabler to the 22% improvement is the final drive ratio."

And if you read the study they actually used a 4.5:1 FDR because they thought the theoretical FDR of 3.766 computed from the AMT transmission's top gear at 55 mph and the "selected efficient portion of the engine map" (1200 RPM) wouldn't provide enough power resulting in "frequent down shifts with increased grade, cargo weight, frontal wind or similar loads".

The use of 3.90 with the lower gearing of the Allison's 6th compared to the ATM's top gear puts us somewhere between the theoretical efficiency RPM and what they actually tested. Very interesting.

I don't have any problems with frequent downshifting on grades - I do have 40 more HP and 60 more TQ than their test truck also which definitely helps it pull grades at peak torque.

They don't go into any mechanical details about how a 4.5 FDR was accomplished with the hub reductions in place (or if they were removed) - a 2.25 ring and pinion? Possible I guess..... my Trans Am came with a 2.77 but dang that's going to have some seriously chunky teeth.

 

[Xengineguy]

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.
View attachment 897297

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.

Snake oil, that’s cute! What would you name these hubs? Super hi speed ?? I won’t say what I actually think, that would probably get me banned. You would like that I bet. I have no affiliation with General Disorder and can assure you he paid full price for his hubs! So what’s wrong with helping someone on the forum?? There are many people that would like to keep selling
3:07 or whatever gears, if you want that fine! Remember your only turning the gear reduction faster making more noise and heat!
My ECO HUB snake oil hub sets will kill the 3:07 market ………. not my original intention but now I think it is.
.

 

[fuzzytoaster]

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

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.

.. is how I read your post. You completely missed my point to try to "one up" me needlessly. You, me, and everyone else who has been around FMTVs knows that's not the standard tire rating. G/14 ply with a max rated speed of 55 mph is the standard. The K range are indeed rated for the 110km/68mph but that's still less than the trucks are able to go with gears or Eco hubs. They're not on 99% of the FMTVs out there so my point of safety remains valid regardless of 395/85r20 used.

If people do the ECO hubs they will need their ECM adjusted, which can be provided by you. That is being affiliated by profit.

 

[GeneralDisorder]

View attachment 897332

.. is how I read your post. You completely missed my point to try to "one up" me needlessly. You, me, and everyone else who has been around FMTVs knows that's not the standard tire rating. G/14 ply with a max rated speed of 55 mph is the standard. The K range are indeed rated for the 110km/68mph but that's still less than the trucks are able to go with gears or Eco hubs. They're not on 99% of the FMTVs out there so my point of safety remains valid regardless of 395/85r20 used.

If people do the ECO hubs they will need their ECM adjusted, which can be provided by you. That is being affiliated by profit.

DUDE! Where did you get my picture!? That's amazing - I look exactly like that BTW. I'm quite a bit more bald though and my glasses are thicker and my lower lip can't cover my teeth quite as well but hey - that was probably using a Beauty Filter on my phone. I'm flattered

I don't charge much for the programming all things considered and it's of no real consequence to my income. Mostly doing it to spite CAT and their assholery of not re-rating my engine.

I am curious though - I didn't look at my original 2008 MV/T's - are they different in terms of speed rating? Has that changed over their production because if it has that's news to me and I legitimately assumed that all MV/T's produced carried the same speed and load rating..... is that incorrect?

The Michelin's should be swapped out immediately if you have those. They are all old enough at this point to be way past their safe use - especially at high speed.

Sure - I can go faster than 68. I rarely do in practice though due to fuel economy. And brand new MV/T's with a K speed rating are going to be fine. Being MILSPEC they are x-rayed for defects and are probably tested to 200% of every specification. If you have tire's that aren't old and rotten they are going to be fine at any speed we can achieve. I haven't seen a single report of accident due to FMTV tire failure at any speed - have you? I would be interested to read it.

 

[Awesomeness]

That is an interesting study, they were able to gain 22% efficiency out of the FMTVs by testing other transmission and gear ratio combinations.

I my opinion, the most relevant part from their conclusions to this discussion: "The key enabler to the 22% improvement is the final drive ratio."

They are good studies.

The couple lines before that are equally important to our discussion here: " These fuel economy gains can be attributed to the greater efficiency of manual transmissions and the increased number of gears available in these transmissions to keep the engine operating in its most efficient region. The key enabler to the 22% improvement is the final drive ratio. "

They are adding 2x more gears, narrower together in ratio, then adjust the final drive ratio so that the transmission's gearing lines up with the engine power curves. Removing the 2:1 hubs does the opposite, turning your transmission into a 4-speed, still with the non-trivial inefficiencies of the automatic.

Here are two of the other FMTV studies, that I had saved off, but there are others as well.

 

[GeneralDisorder]

The automatic is not significantly more inefficient when the TC is locked. Why do you suppose the ENTIRE automotive industry has adopted automatics for better fuel economy and control? Also it's a 5 speed up to their test speed not a 4 speed, and if you surpass 65 mph you can easily get into 7th gear making it a 6 speed. My 3700SP works great along side the ECO hubs. I daily drive my truck, do all my own work, and if it sucked at any aspect of how it operates you can bet I would switch back in an instant - it wouldn't cost me a dime. So what exactly is my motivation to continue to defend my position here? If you think a couple of $400 ECM flashes is the reason you are sadly mistaken - I don't own a performance shop with a chassis dyno to make $400 once every couple months when someone decides they need their speedo to read correctly. I have a $40,000 saltwater aquarium in my lobby - this service ain't even paying for fish food pal.