ShinerBock wrote:
The two extra gears do not help in highway driving. Most of the time you are in your final gear unloaded. The Ecodiesel in that review actually had worse gear ratios in this instance. The Ecodiesel had a 3.55 rear gear ratio and the final gear of the 8HP70 is .67:1. The Cummins on the other hand had a 3.42 rear gear and the final gear of the 68RFE is .62:1.
In real world driving I think it does help some. All highway driving is not steady state on a level road. I find the 8 speed in my car will quite often drop a gear when conditions change slightly. It lessens the amount of boost required in a given situation. This is with an engine that makes peak torque at 1600 RPM so it isn't shifting down because it can't make enough power without downshifting.
I do agree with you that the big difference is in the masses involved. The larger moving engine components, their larger bearing surfaces and the bigger pumps required to lubricate and cool them. Heavier transmissions, transfer cases, axles, brakes etc will all require more power to turn. The IFS half ton also sits lower than the solid axle HD truck and will have a bit of an aerodynamic advantage.
I can't remember the cooling fan ever coming on when running empty at highway speeds in my 6.7 or the 5.9 that preceded it.
