ECO Hubs Who needs 3:07 gears?

[Ronmar]

Ok, on that tune you are probably going to ramp pretty steadily from ~300ft/lb at idle to ~800 ft/lb at 1450RPM. Thats ~72 ft/lb of increase per 100 RPM. If you advance the pedal slowly and note at what engine RPM the truck starts to move, we can get an idea how much engine torque it is taking to pull your truck up that 10%/5.7deg slope. And of course how accurate is that 10% slope number Details details...

 

[MatthewWBailey]

Ok, on that tune you are probably going to ramp pretty steadily from ~300ft/lb at idle to ~800 ft/lb at 1450RPM. Thats ~72 ft/lb of increase per 100 RPM. If you advance the pedal slowly and note at what engine RPM the truck starts to move, we can get an idea how much engine torque it is taking to pull your truck up that 10%/5.7deg slope. And of course how accurate is that 10% slope number Details details...

I'll go measure it. I have a 12' level

 

[MatthewWBailey]

I'll go measure it. I have a 12' level

And of course how accurate is that 10% slope number Details details...

Here's the measurement. It's only a 40' section of driveway but rises at 9.75 degrees. I was surprised it was that much. No wonder I spin around when plowing snow. The backhoe does a 180 on that spot without my chains. So that comes to 17% grade.
It's a pain bc I have to stop dead on that rise for traffic to pass.

 

[Ronmar]

Ok, so nearly 10deg not 10%… be curious what engine RPM it takes to get you moving on that slope…

 

[MatthewWBailey]

Ok, so nearly 10deg not 10%… be curious what engine RPM it takes to get you moving on that slope…

I'm rigging up my tach off the alt R terminal just to test it. I can use the spare/unused 568A energize wire from K11 since it's already up in the PDP. The delco instructions say 10pulses per rpm, then I got the pulley ratio too. I think that's 2.5:1

 

[Ronmar]

I came across someone who had a driveshaft failure(non eco hub LMTV) that split the tube. He was able to measure the tube thickness and he came up with .134” wall thickness. That is the heavier of the two specced wall thicknesses, found on the #6500 peak torque version…

 

[Ronmar]

Tach goes in on Tuesday lol. Weight was 17400 at the last scale i was on. Rpm sounded like the same level as the high idle but it's just a swag.

A 17,400# truck should require 3,021# of thrust to crawl up a 10* slope. With the 70/30 torque split in 2nd gear, thats,~453# for each front tire and 1057# for each rear tire. So 1057# times 1.942’ tire radius = 2053ft/lb on each rear axle, so 4106 total out of the rear diff, divided by a 3.07 diff = ~1370ft/lb from the rear driveshaft to produce that much tire thrust and about 647ft/lb from the front DS. Thats ~2015ft/lb total from the transmission to make ~3000# of thrust. With a 4.18 total ratio in 2nd gear and considering gearbox losses, thats ~540ft/lb out of the torque converter into the coupled 2nd gear ratio.

Here is where the math gets a little muddier… Low-mid range torque converter multiplication is a little more difficult to estimate as the multiplication increases with the difference between input RPM and turbine/output RPM. And of course the magic of the TC is it will match output to load. The 275hp 3126 tune will deliver from ~400-800 ft/lb between 800 and 1450 RPM? and the torque it delivers will mix with that variable torque multiplication until it reaches stall or the turbine output shaft starts to rotate. But since the required torque of ~540 ft/lb falls in your available range of 0-~1600 ft/lb it obviously moves. If we know the RPM it takes to start moving on that 10* slope, we can estimate engine produced torque, and then estimate converter multiplication at that RPM difference when the truck just first starts to move. In the end it should only take about 1/3 of what you are capable of delivering into the gearbox…

You want to advance the pedal slowly, as it is a speed selector not a throttle. The pedal tells the governor or ECU what RPM to run at, and it in turn delivers fuel as it is “programmed” to achieve that commanded RPM… if it sees a big difference between actual and commanded RPM, it will throw a lot of fuel at it making it difficult to capture the RPM when it first starts to move on the slope… ideally you would want to have someone chock the wheels so you could start from setting against the chocks to take any possible brake resistance out of the picture. You should also be able to hover using the pedal to vary RPM, at a particular spot uphill from the the chocks or once your foot is off the brake after you start normally…

 

[MatthewWBailey]

A 17,400# truck should require 3,021# of thrust to crawl up a 10* slope. With the 70/30 torque split in 2nd gear, thats,~453# for each front tire and 1057# for each rear tire. So 1057# times 1.942’ tire radius = 2053ft/lb on each rear axle, so 4106 total out of the rear diff, divided by a 3.07 diff = ~1370ft/lb from the rear driveshaft to produce that much tire thrust and about 647ft/lb from the front DS. Thats ~2015ft/lb total from the transmission to make ~3000# of thrust. With a 4.18 total ratio in 2nd gear and considering gearbox losses, thats ~540ft/lb out of the torque converter into the coupled 2nd gear ratio.

Here is where the math gets a little muddier… Low-mid range torque converter multiplication is a little more difficult to estimate as the multiplication increases with the difference between input RPM and turbine/output RPM. And of course the magic of the TC is it will match output to load. The 275hp 3126 tune will deliver from ~400-800 ft/lb between 800 and 1450 RPM? and the torque it delivers will mix with that variable torque multiplication until it reaches stall or the turbine output shaft starts to rotate. But since the required torque of ~540 ft/lb falls in your available range of 0-~1600 ft/lb it obviously moves. If we know the RPM it takes to start moving on that 10* slope, we can estimate engine produced torque, and then estimate converter multiplication at that RPM difference when the truck just first starts to move. In the end it should only take about 1/3 of what you are capable of delivering into the gearbox…

You want to advance the pedal slowly, as it is a speed selector not a throttle. The pedal tells the governor or ECU what RPM to run at, and it in turn delivers fuel as it is “programmed” to achieve that commanded RPM… if it sees a big difference between actual and commanded RPM, it will throw a lot of fuel at it making it difficult to capture the RPM when it first starts to move on the slope…

It barely starts moving at 1200rpm from a dead stop on the slope. I was barely on the throttle. It kept moving steadily, barely, until I got to the top and then started accel.

With the tach in there, it's easy to see your point in the last paragraph. I was driving up the hill back to the house which is a steady 6% grade at 44mph and 1600rpm. I just tried to hold 1600 and I could hear the engine getting louder as the slope increased to 7% on the last section bf my house.

if I hold pedal steady on flats, it's shifting at 1850.

also interesting from your calcs that "thrust" to get moving is almost exactly the vertical lift component of the weight at 17.3%, grade is 17.18%. Neat

 

[MatthewWBailey]

You should also be able to hover using the pedal to vary RPM

It was holding at 1100rpm. I came off the brake and let it sit for a second at 1100. Had to get to 1200 to start creeping. But it did start accelerating at 1200 albeit slowly. So maybe 1150 is the threshold

 

[Gunny 0369]

Mileage update: ~25k pounds, 6x6, 3.09's, Goodyear MVT's, big box on back (12' 4" high, 8' wide), kept speed at or below (most of the time) 65 mph

Portland, OR to Henderson Utah; 887 miles, 108.9 gal gives 8.13 mpg.

No issues with drivability.

more of this.

ckouba, what terrain were you on, and did you climb any mountain passes?

Im about the same size as you, no ECO, averaging 7.2 mpg - best 7.7 worst 4.8 (headwind) 5500 miles NC to MT, Canada and back) passes are slow, down to 35-40 on the climb up the 9600 footers.
3116 ATTAC mechanical A0.