Duramax vs Power Stroke Fuel Economy Tow Test and Drag Race
Enjoy... Fuel Economy Test: Power Stroke: 7.8mpg Duramax: 6.9mpg Link
Forum Discussion
ShinerBock wrote:4x4ord wrote:
It would be interesting to see the brake specific fuel consumption graphs for these engines. You'd expect the transmissions to shift according to fuel usage.At 1800 rpm these engines can produce over double the power that is needed to tow a typical 5ver down the highway. I'm surprised lower rpm wouldn't save a little fuel. A general rule is that higher cylinder pressure produces greater efficiency. If you're running higher rpm than is needed the engine is operating at a lower cylinder pressure than it could be.
On flat ground under low load the fuel economy is better in 6th, but on hilly roads, a lot of wind resistance, or in other situations that put more load on the engine it is is not in my experiences. In 6th and under higher loads, it feels like the engine has to add more fuel/air to compensate for the lack of torque from a taller gear ratio and the lack of horsepower from being at a lower rpm. In 5th, it feels like it does not have to add that much fuel(fuel pressure is lower) and boost to do the same work. There is less load on the engine in 5th even though it is at a higher rpm. There is also the factor that EGT's are lower by about 200F as well.
Under part throttle at a constant speed the power at the rear wheels is the same regardless of the engine rpm so the difference in the amount of fuel burned per time will be close. (it will vary by the difference in efficiency which usually favours the lower rpm). However, the fuel burned per power stroke will be higher with the engine running slower, so higher exhaust temperatures makes perfect sense. (roughly the same amount of fuel but more air at higher rpm) When the truck is working very hard it makes sense that it would get its best fuel economy at 1800 rpm but, if it's working hard at 1800 rpm it would be getting absolutely terrible fuel economy.
Edit: I hope I'm not coming across as being argumentative, I'm just thinking about what you're saying and trying to understand the physics of it.
