My G35 is automatic 5-speed. I do a lot of highway with it.
At 120 K/h, the RPM is approx. 2750. I know that if I cruise at 100 K/h, the RPM is approx 2500 and at the same time I can attain a much better mileage.
I was told that one can change the settings (Oil Pressures) in an auto transmission in order to speed down the engine and thus save fuel?
Is this possible? Thanks for replying. Regards.

 

no...the gears in the trans, as well as the gears in the diff, and the T.C. locking up or not determine how fast your engine needs to spin at a given speed.

 

you could buy taller tires for your car... like go get some 215/60 series tires. This will cause your speedometer to be slow (i.e. it will show 60mph when you're going 62mph), but your engine will spin slower since you are traveling farther for each tire revolution. You can also look at it this way: your engine will be turning fast enough to push your car 58 mph, but you'll actually be going 60mph. Sorry, don't know the km/h conversions, but I think you get the point.

max

 

Unfortunately V6 with 24 valves [even 3.5 liter ones] have a tough time generating enough torque at low rpms. [Because they are tuned to create high rpm power to excel in magazine test to sell better] ........to function with AC on, going up inclined roads [slight hills] at 55 mph. They thus down shift frequently if car is fully loaded.

Manufacturers balance rear diff ratio and tire diameter to function ok in worst case conditions at the same time trying to minimize fuel consumption for EPA highway test [for which they pay a tax penalty].

If they didn't have to consider the fully loaded potential extra weight [5 fat people with luggage] things could be 5-10% better mpg wise........by running cruise [5th gear]at a lower rpm.