is it better to go with the flow on the hwy?

[CosmicMC]

Originally Posted by Capcom

In a modern fuel injected car, best mpg is at the lowest possible speed at the highest possible gear.

In theory, perhaps that's true, but I don't know if that's necessarily true in practice. It would have to be plotted on a graph with a scan tool. It's possible that on some cars the engine would have to work so hard at that low RPM to overcome wind resistance that it would actually be more efficient at a higher RPM. It would also depend on when the lockup torque converter kicks in. I don't know for sure, I'm just proposing the idea for testing. My theory is that it depends on the car. If the torque output of the engine is low enough at say 1000 RPM, it's possible higher RPMs would actually increase the fuel efficiency. Say the car hits top gear at 38 but the torque converter doesn't lock up until 40. You'll get better mileage by accelerating slightly until the TC locks up.

On my car, the sweet spot is between 45 and 50. The lockup torque converter kicks in at 42 MPH under low acceleration, so the car is in highest gear and the torque converter locks up at 42, but the mileage peak isn't until about 47. Admittedly, that's rough estimation based on the car's "Instant MPG" dash readout, but I'm reasonably sure the sweet spot is not at lowest RPMs in high gear.