How Much Horsepower Required to Cruise Comfortably at 70 MPH?

My Ford Ranger has a 4 banger. My Ram 1500 quad cab has a 5.7. You’d think the Ranger would be the go to vehicle for gas mileage right? Well around town yes but on the highway, not so much. I’ve had as bad as 17 mpg out of the Ranger before with a head wind. My RAM usually gets 19-20 and has a much larger frontal area obviously. But the power to weight ratio and torque is so much higher, the engine doesn’t have to work that much to keep it at speed. That Ranger pedal stays to the floor in a head wind though. I’ve seen the same results between motorcycles that have different size engines. The “powerful” bikes could go further on a tank of fuel than the lower powered bikes because the powerful engine just isn’t working as hard to keep speed. So with what you’re talking of doing going to a 340, build it with a lot of torque. Low end torque. Everything will improve for you.