Eco Hubs 3.90 or 3.07 for Best Fuel mileage

[Ronmar]

From sizing gentlest, I think of this as an analysis of Energy output and torque output. Torque is not energy, so it's a 2 part checklist. Enough torque to move the shaft at 1440, checked. Enough energy (Hp) to overcome wind and grade at 55 at 1440, not checked. Hence why after the 330 remap, I can maintain 52 up a 7% grade whereas before at 275, only maintained 43, with same gearing and almost identical torque curve of engine.

Torque IS what does all the work. HP is simply an expression of torque over time and represents the speed at which you can perform a particular task or the volume of work in a given timeframe. it was an expression of energy output created by james watt to sell steam engines to people who had only ever used and understood horses as a prime mover. Been confusing how things work ever since

Something often overlooked is that it only really applies if you have enough surplus torque to actually perform the work at that RPM.

I prefer to think in terms of torque, or surplus torque, which is actually what the torque number is, what is left over to do work after the crank is spun to a given RPM. Thats why the number decreases above pk tq rpm as the pumping losses are consuming more and more of the surplus, as the pulses also get shorter. You only typically have 1/2 the available torque at pk hp as you do at pk tq…

Say are running along near peak HP RPM and run up on a slight hill. Even at full fuel the amount of surplus TQ you have is not enough to maintain speed so your speed and RPM decreases, back toward where you have more surplus tq until you reach the point where surplus tq = load. You have just re-defined your engine HP based on your available tq output

Dealing in terms of torque is simpler. The behavior in terms of tq also explain the better road performance reported on ecohubs. Say you have installed Ecohubs and are now tooling along at close to pk/tq RPM instead of pk hp RPM And roll up on that same slight hill. You already have the potential for nearly twice the available surplus torque, and the governor/ecu simply burns more fuel till torque and load reach equilibrium, all without loosing any speed… and on level ground you are not burning all that extra fuel to overcome the added pumping losses between pktq and max governed RPM. Like driving with an exhaust brake on…

 

[MatthewWBailey]

what is left over to do work after the crank is spun to a given RPM

Im not arguing and Yes I agree but as soon as you mention torque AND rpm, your are dealing in energy, wether you call it watts, HP, kCal or BTU's, joules. Doing "work" is energy. You can't size an engine on torque alone, so how is it simpler? On this 3126 engine the "high torque" 275hp curve is very nearly the exact curve as the 330hp curve and the peak torques listed are identical. There are no circumstances where one would mention torque without rpm, which means you're talking HP, unless it's a static condition like a torque wrench or bolt "torqued to spec". And you can't calculate surplus torque until you've established the balance point, which is energy out = energy of load to maintain a static velocity. You can have 860ft-lbs of torque that can't move a vehicle up a hill more than 1mph and 860ft lbs of torque that can go 55mph up the same hill. Difference is there's no energy info describing either scenario.

This debate always ends up in a circular path bc the units are linked by time or time-rate. So it becomes inconsequential as to which is more important. But In Thermodynamics, only energy is considered. In genset sizing, only hp vs kw is considered at 1800 rpm fixed, which automatically infers a torque value.

 

[Ronmar]

Well of course it is energy, But you can take RPM out of the equation. I only need mention RPM in the sense that there is a particular one in a given engine configuration where the engine can produce peak torque. You have a certain gear ratio and a certain amount of torque which in conjunction with the tires provides a certain amount of thrust. You have a certain amount of load to perform a particular task. If you have more torque and mechanical advantage than load you can accelerate and change gear ratios to perform the task faster.

If you acquire more load than available torque and gear derived thrust, you will slow down… torque IS the prime factor in choosing an engine. You need enough to provide for the task you require and varying that available torque will decide the rate or economy at which you perform that task… RPM, whats RPM? HP? Meaningless without enough torque to actually perform the task And more tq = faster work… Simple huh…

those torque curves you mention may be similar, but they cannot be identical, or you would have the same HP figure. Again, it is based on torque over time. No torque, no work

You noted that pk tq didn’t really change between the tunes, because the tunes don't really alter the flow characteristics(maybe slightly if they alter boost) determined by bore, stroke and the flow thru manifolds, head ports, valves ect. So the peak volumetric efficiency point doesn’t change. They are burning more fuel on the backside of the power curve, which flattens it out a bit delaying the decay and bumping up the HP number by burning more fuel and creating more heat to further offset pumping losses… but if you encounter a situation that requires that peak torque value, they will both wind up in the same place, in the same gear at the peak torque point…

 

[Keith Knight]

Let’s get back to the bottom line. Driving a 3126B 330 hp 3.90 gears and eco hubs 85psi tires, give it the perfect driving conditions on a flat road.

What gear and speed would obtain the optimal RPM for the best fuel economy?


I understand other factors like weight, wind etc….. come into play. We can say average weight is 23,000lbs or whatever average weight you smuggest.

 

[hike]

Let’s get back to the bottom line. Driving a 3126B 330 hp 3.90 gears and eco hubs 85psi tires, give it the perfect driving conditions on a flat road.

What gear and speed would obtain the optimal RPM for the best fuel economy?


I understand other factors like weight, wind etc….. come into play. We can say average weight is 23,000lbs or whatever average weight you smuggest.

My two cents:

For balanced performance and fuel efficiency 3126B 330 hp 3.90 gears and eco hubs 85psi tires spin 2000rpm at 60mph in 5th gear
CAT suggests: 2000 rpm @ 60 mph (97 km/h) subject to the following: Maximum cruise speed of 65 mph (105 km/h) or below. Maximum recommended engine speed at cruise — 2400 rpm. Minimum recommended engine speed at a cruise speed of 55 mph (89 km/hr) — 1800 rpm.

This is right where the EcoHubs put the 3.90's

Peak torque is 1440 rpm.

For fuel efficiency 3126B 330 hp 3.90 gears and eco hubs 85psi tires spin 1600rpm at 60mph in 6th gear.

I haven't taken a long trip to check real mileage per gallon at weight as yet, though watching the CAT ECM instant fuel reading on our Bluefire it hovers 11-14 on the flats in 6th at 60mph. That is my goal for now.

One of the things I do notice on mild hilly drives is the Allison downshifts a bit lower than I might if I was pushing a stick around—

 

[Keith Knight]

Thank you all for all the helpful data.
I want to see instant fuel mileage.
What is Bluefire?
Part number?

 

[Ronmar]

That suggestion from cat sounds a little off to me, at least based on what I typically observe… for economy, the engine is usually operated on the front side of the power curve, not the backside. For instance my truck and 4runners make pk hp at ~4800, pk tq ~3600 but highway cruise @60MPH ~2200RPM…

with the tire size and gears, a final ratio of 3.9 in 6th gear will give me ~61MPH @1550RPM like Hike mentioned. With slope, speed/drag remaining the same i am certain I will have worse fuel economy in 5th@2000 RPM because I have to pay for the added pumping losses above pk torque…

it might be better in 7th which would put me ~1350 RPM @60MPH, this might be more ideal for the 3126/c7 with their lower pk tq points, but you at some point reach a situation where you loose too much efficiency lugging the engine while trying to get its maximum available tq at the lower RPM. You also have more difficulty building boost efficiently at low RPM, so too low is as bad as too high and you will wind up back toward pk tq… i will try it at some point, but I have a lot of work to do before I get there… fuel flow would be nice, but I don’t have it on my mechanical:O

 

[hike]

That suggestion from cat sounds a little off to me, at least based on what I typically observe… for economy, the engine is usually operated on the front side of the power curve, not the backside. For instance my truck and 4runners make pk hp at ~4800, pk tq ~3600 but highway cruise @60MPH ~2200RPM…

with the tire size and gears, a final ratio of 3.9 in 6th gear will give me ~61MPH @1550RPM like Hike mentioned. With slope, speed/drag remaining the same i am certain I will have worse fuel economy in 5th@2000 RPM because I have to pay for the added pumping losses above pk torque…

it might be better in 7th which would put me ~1350 RPM @60MPH, this might be more ideal for the 3126/c7 with their lower pk tq points, but you at some point reach a situation where you loose too much efficiency lugging the engine while trying to get its maximum available tq at the lower RPM. You also have more difficulty building boost efficiently at low RPM, so too low is as bad as too high and you will wind up back toward pk tq… i will try it at some point, but I have a lot of work to do before I get there… fuel flow would be nice, but I don’t have it on my mechanical:O

I agree CAT's suggestion surprised me, too. Though that is a quote from their spec sheet for 'balanced performance and fuel efficiency'. Attached sheet to post #17.

Our M1078A1 with the 330hp tuned 3126b doesn't like 7th gear at 60mph. We have to go faster than we wish to get into 7th, then slow down, though it is hard to hold 7th. With the EcoHubs the Allison prefers 6th gear on the highway.

I haven't explored the Allison software and shift points well enough to begin thinking about changing them for better fuel efficiency—

 

[Keith Knight]

What is Bluefire?
Do you have a part number?

 

[hike]

Thank you all for all the helpful data.
I want to see instant fuel mileage.
What is Bluefire?
Part number?

Bluefire makes a 9 pin adaptor and app to read various systems from J1939, J1708 and CANBUS. We have one, though our military systems offer more a teaser of information than enough to build a glass dash. You have to convert or add a 12v connector to the connector at your left knee to use the Bluefire.

The instant Fuel Economy, Average Fuel Economy and Fuel Rate are interesting, though as text gauges difficult to follow trends while driving—

 

[Ronmar]

A scangauge D might also be able to read and display the bussed data, as well as deliver live consumption/mileage info.

 

[Keith Knight]

Bluefire makes a 9 pin adapter and app to read various systems from J1939, J1708 and CANBUS. We have one, though our military systems offer more a teaser of information than enough to build a glass dash. You have to convert or add a 12v connector to the connector at your left knee to use the Bluefire.

The instant Fuel Economy, Average Fuel Economy and Fuel Rate are interesting, though as text gauges difficult to follow trends while driving—

Is there a particular model that you like?
Is our Data port 24 volt?
If so how did you change it to 12v and does that affect it when using the data port when connecting to my computer for diagnostic purposes?

 

[hike]

Is there a particular model that you like?
Is our Data port 24 volt?
If so how did you change it to 12v and does that affect it when using the data port when connecting to my computer for diagnostic purposes?

We have a 9 pin adaptor.
Our data port is 24v. We bought a splitter and replaced the 24v feed wire on one with a 12v feed. Now we have two 9-pin ports at our left knee, a 12v and 24v.

I was hoping to use the bluefire to create a glass dash, though our ECU/ECM systems and the bluefire share incomplete data. You can set your own colors, fonts, sizes, placement, which gauges to view, even have multiple pages. If you have a habitat connected to J1939 sensors you likely could see water, battery and habitat air temperature, too. In the future I am hoping to learn how to create additional gauges to harvest more information, or use information better.

For example. Blue fire can see the CTIS PCU air pressure, though most of the time the PCU reports 0. The bluefire is setup to read a TPMS system, though I am not planning to add that. I expect one could program Bluefire to capture and hold the PCU test pressure, though have yet to attempt that.

Another example: the CAT ECM can read the oil pressure, Though we don't have that OEM capability through the ECM across J1939. Our trucks have two oil pressure sensors: One feeds the dash gauge the measured pressure seen; the other feeds the K11 whether the pressure is over/under a set limit (15# I think).

Anyway. I like having Bluefire on long drives. We have RPM, gear, turbo boost, speed, water and transmission temperature, and instant and average fuel efficiency for the life of the vehicle, (I haven't figured out how to get trip mileage and trip fuel average to work as yet). Fuel rate per hour is one I am fussing with, too. I can set up our mapping: Google, Gaia, and Spyglass to switch between them all at will on a mounted iPad while cruising.

The Bluefire is a small community, mostly of RVer's that has very limited support resources. No subscription cost, buy the adaptor, download the app. and go If I spent more time in the backside configurations to create more gauges specifically for our platform I am pretty sure it could become quite useful—


Our current Bluefire dash layout

 

[GeneralDisorder]

For example. Blue fire can see the CTIS PCU air pressure, though most of the time the PCU reports 0. The bluefire is setup to read a TPMS system, though I am not planning to add that. I expect one could program Bluefire to capture and hold the PCU test pressure, though have yet to attempt that.

Yeah if there is algorithmic level programming available it should be trivial to update and hold the last pressure reading anytime the reading jumps above 5 psi. Just watch it on the back end and when it sees the reading go high capture that number and display it till the next reading takes place......

Another example: the CAT ECM can read the oil pressure, Though we don't have that OEM capability through the ECM across J1939. Our trucks have two oil pressure sensors: One feeds the dash gauge the measured pressure seen; the other feeds the CAT ECM whether the pressure is over/under a set limit (15# I think).

So the Bluefire doesn't see the C7 oil pressure reading? Hhhmmm - this guy is using the Bluefire on a 3126B and he has oil pressure on his tablet. Go to 13:00 in this video and he shows the reading with his new pump. Also his truck appears to have the same Medallion MMDC system as our A1R's - the annunciator panel is identical (different indicators but same part):

The Bluefire is a small community, mostly of RVer's that has very limited support resources. No subscription cost, buy the adaptor, download the app. and go If I spent more time in the backside configurations to create more gauges specifically for our platform I am pretty sure it could become quite useful

Is it just a custom app with a bunch of settings in drop-down menus or does it have actual algorithmic capability with a scripting language, etc? I've held off buying one since I'm not sure how useful it would be and how much data it is programmed to understand and if that can easily be extended.... would like to bring the Niehoff alternator's J1939 data into the bus and display that as well - it has alternator RPM, temp, and both system voltages. I have used DG Diagnostics to pull the data so I know it's sending the generic alternator PID's.

 

[hike]

Yeah if there is algorithmic level programming available it should be trivial to update and hold the last pressure reading anytime the reading jumps above 5 psi. Just watch it on the back end and when it sees the reading go high capture that number and display it till the next reading takes place......



So the Bluefire doesn't see the C7 oil pressure reading? Hhhmmm - this guy is using the Bluefire on a 3126B and he has oil pressure on his tablet. Go to 13:00 in this video and he shows the reading with his new pump. Also his truck appears to have the same Medallion MMDC system as our A1R's - the annunciator panel is identical (different indicators but same part):

Is it just a custom app with a bunch of settings in drop-down menus or does it have actual algorithmic capability with a scripting language, etc? I've held off buying one since I'm not sure how useful it would be and how much data it is programmed to understand and if that can easily be extended.... would like to bring the Niehoff alternator's J1939 data into the bus and display that as well - it has alternator RPM, temp, and both system voltages. I have used DG Diagnostics to pull the data so I know it's sending the generic alternator PID's.

1— I agree. As yet I have not taken the time to learn the backend of the Bluefire software;

2— We have a 3126b, no idea what Bluefire sees from the C7, @Third From Texas has a Bluefire adaptor The RV OEM apparently wired the oil pressure sensor to feed the J1939 system.

According to the CAT 3126b schematic there is an CAT option to deliver oil pressure to the ECM, though I have yet to find a reading in either the DG, CAT ET, or Bluefire software. Bluefire has the ability to read an oil pressure data stream, it does not find one in our J1939 data and neither does the DG or CAT ET software. On our unit (others may be different?) low oil pressure light is on at the moments of starting and quickly goes out; our dash oil pressure gauge works as expected. So, the two sensors appear to be working and either are sending data using different parameters to identify them in the data stream, or they are not in the data stream.

PDF attached as well.

Looking to the M1078A1 schematics it appears neither oil pressure sensor is routed through J1939: low oil with K11 to the idiot light (6 127 and 3 37), the other directly to the gauge (3 5). I wish I had photographed the ECM harness pins when I had them off to compare them to the schematics pinout on the last page. When I add the pin(s) for cruise control I'll look to add the oil pressure sensor, too, if able.

3— I haven't studied the backend side as yet. Though I expect once I learn enough about how different parameters are shared in the J1939 data stream one can create gauges and text displays as desired. Currently yes I am selecting/configuring pre-made gauges.

Once we put the cab interior all back together learning how to program and create in Bluefire will become a higher priority—

 

[Keith Knight]

That’s awesome!!!! Going to order one and thanks for the adapter info. By chance do you remember witch pin is the 24 volt?

 

[hike]

That’s awesome!!!! Going to order one and thanks for the adapter info. By chance do you remember witch pin is the 24 volt?

As I recall 'A' is ground, 'B' is power.
I clipped the red wire on one of the "Y" connectors and attached to 12v feed. The Bluefire adaptor hasn't burned yet—

 

[Keith Knight]

Found it looks like B

 

[Keith Knight]

Easy enough! Thanks for all the help. I’m currently working on changing all sorts of stuff on my truck.

 

[Keith Knight]

Bluefire makes a 9 pin adaptor and app to read various systems from J1939, J1708 and CANBUS. We have one, though our military systems offer more a teaser of information than enough to build a glass dash. You have to convert or add a 12v connector to the connector at your left knee to use the Bluefire.

The instant Fuel Economy, Average Fuel Economy and Fuel Rate are interesting, though as text gauges difficult to follow trends while driving—

Hike, did you run constant 12v or ignition 12v for the BlueFire port?