Gas mileage: Powerband vs RPM

[Breezybro]

I've been reading around the internet after seeing the DFCO thread and have been wondering.. I know the powerband is where the engine is the most efficient.. and I also know when I had my rental Infiniti with manu-automatic option, I got better gas mileage going 75 in 5th with higher rpms than going 75 in 7th with lower rpms.. so it made me question the validity of having lower RPMs as being the obvious answer.

Does anybody have anything they would like to share, or any information? I would be more than appreciative. Thank you!

 

[ahtoxa]

It's all about load, really. The engine can spin higher and get better fuel economy if the load is too great for a given taller (higher) gear.

 

[Breezybro]

Well, that is good to hear, at least that means I don't have to strive for the lowest RPM all of the time!

 

[SonicBoy24]

I had my rental Infiniti with manu-automatic option, I got better gas mileage going 75 in 5th with higher rpms than going 75 in 7th with lower rpms.. so it made me question the validity of having lower RPMs as being the obvious answer.

As was already said, its all about the load on the engine. Just like with our Sonics, sure, you can put it into 6th at 35mph, but the load on the engine is extreme and you won't get any acceleration at that point.
At the same time, putting on Sonic into 4th at 80mph will cause your mpg to plummet.

It all depends on the load and the gearing of the transmission.
Ordinarily, lower RPMs are the best for mpg as long as you aren't stressing the motor.