Cummins power
The class A's that I am like have the Cummins engine. I notice that the larger/heavier rigs have more horsepower (300hp vs. 340 to 360hp)with the 6.7 L engine (same torque). How do they get the extra ...
Forum Discussion
moisheh wrote:
mcdamarell. If your company simply limited the speed to 63 then mileage had to improve. There is no argument that slowing down increases MPG. Trucking companies with 3000 or more tractors usually limit the speed and they ALL get better mileage. Proven fact!
Moisheh
More too it than just reducing speed to save fuel and yes I drive my pickup based on the sweet spot of the engine torque curve which is around 2,000 rpm or 60 mph with a 4.1:1 rear.
Depends upon the gears and the sweet spot of the engine. If the truck was originally spec'd with tall gears to run at peak torque (around 1,400 rpm in 10th) and then you turn it down mpg will drop. At 62 mph the rpms want to be at 1,300 rpm and fall out the bottom of the torque band. At 65 mph they sit right around 1,400 and the truck runs fine. Not to mention the local speed limit is 65 and now we are a rolling road block. The company acknowledges this but they say the loss of mpg is offset by insurance costs. Since we lease most of our trucks they were geared to run 70 mph. The new 14 speed Volvo's are properly geared and are doing better. In the Detroit engine's program when they limit the speed it limits torque as well. Likewise you can also have two different torque settings (one on cruise and one on the foot) so much depends upon the engines program.
I've driven engines that were turned up and driven the same engines after they were turned down. Mpg has always dropped when the engine is turned down. Just because the engine is turned up does not mean you always have to use it, but when it's limited, it takes longer to climb and longer to accelerate so you end up using more fuel in the long run. That's my 19 years experience.
