Chevy Truck RPM

[bluewoo]

Dodge did something different on the 6.4 liter hemi.

Ram came back with the following explanation.
“Ram Truck ‘invented’ the first gear hold feature – and calibrated it – to avoid gear hunting and driving at excessively high rpm’s. Ike Gauntlet is a variable grade and we worked hard to develop a calibration that appropriately manages torque on this run and other grades. We don’t want the truck to rev high for extended periods of time and purposely hold 4,200 rpm.”
Ram’s engineers considered and accounted for a multitude of factors, including: optimized fuel economy, engine longevity, and driving comfort. The results were inline. The Ram 6.4L HEMI got a better 2.8 MPG on the uphill climb with close to 20,500 lbs of total truck and trailer (GCVW). The engine coolant, oil, and transmission oil temperatures were all controlled and well within limits. There was no gear hunting and no high revving. However, the speed up the hill did suffer, and the truck slowed down to just below 30 MPH at the end. This is about the same speed as fully loaded semi tractor trailers are doing. This stretch of I-70 does have three lanes, but if you meet a big and extra-slow semi in the right lane, then it’s very challenging to try and pass. An open day like during the test is nice, but the regular flow of passenger vehicles is moving at 60-65 MPH and making a pass at 29 MPH is not easy.

2014 Ram 2500 HD 6.4L HEMI and Gear Hold Feature [Ike Gauntlet Video] - Truck News, Views and Real World Reviews

[Jim Schings]

Originally Posted by Tonkatoy77

I have always been taught that engine load is based on air flow vs. fuel used.

Air Flow vs fuel used (in mass) is simply the air fuel ratio. It varies from 14.7 to 1 to 12 to 1. (In a gas engine.) It has nothing to do with load. In a diesel, this is not typically even applicable but the range is much wider and much more complex.

I have never used the equation you are using to determine engine load. And neither does combustion engine manufacturers.

Really? It is one of the most common of all formulae used in physics and especially in reciprocating engines of all kinds. It is this formula: 33,000 ft-lbf/min adjusted for rotating motion. Guy named James Watt came up with it...

Based on what you are saying if I was coming down a 7% grade with my pickup and TT at 2500 RPM's my engine would still be under load. The way I was taught there would be no load because there would be no fuel.

??? In either a diesel or gas engine, there is no HP being developed by the engine when going down a hill. Both engines shut the fuel off when decelerating. Look at the formula again. Torque would = 0 going down a hill. (actually it would be minus....)

You asked what I am calling load. It would be energy used.

Then the energy used would be in HP, or BTU, or KWH. "Load" could loosely be used when discussing torque, (as in foot lbs. of force)

[AquaMan]

I understand what you are saying by "load". Think about this though, if you cut the throttle in a boat what happens? It slows at a fairly rapid pace (high resistance or load), where a truck/trailer combo will roll for quite a while (lower resistance). Marine applications are some of the most demanding motor applications there are because of this. I've had several supercharged boats that pulled a constant 9-12lbs of boost, depending on boat, and boost only occurs under "load" (or resistance).


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[elchilero53]

My Tahoe has a 5.3L with a 6-speed which I run in Tow/Haul mode while towing our SolAire 20RBS. It has a 3.42 rear end. With everything loaded on board I'm running about 4800-5500 lbs. GVWR on the toad is 7600 lbs. TV tow capacity is 8200 lbs. I run about 2300 rpm on flat ground doing about 60-65 and 2800 rpm in rolling hills. On steep climbs, I'm running 3200 rpm max but I am doing 25 mph when I get to the top. Unhitched, I run 1800-1900 rpm at 75 mph, so the rpms look and sound about right. I was a bit worried at first but the truck hums just fine while towing.

[sail2liv]

3.73 and speed must make difference....6.0 gas 3.73....I95 56-58 mph 8500 lb 5 er...
RPM no tow haul 1700 w th 1900.....10-11 mpg cruise control on unless in hills....
5-6% grade in smokies 2500 rpm 45 mph ....9 mpg......
no trailer cruise on in 6th gear back off to 55 mph 15-18 mpg......no load except wife and some firewood.....