You can see what it does IRL on real roads. This video was done last week and uploaded Saturday 12/7 so cold weather which is very bad for gas mileage because of increased aero drag and rolling resistance. Now my car is going to have horrible aero especially compared to a 1999 Corvette. If I’m lucky I’ll get about 30 MPG highway because of that, but that is still about as good as I got with my 1987 Hyundai with the non-overdrive 4-speed transmission. My best Dallas-Nashville mileage was about 31-32 back in the early ’90s partially because I was driving at night and missed everybody’s rush hours for all the cities I hit. Again, 1980’s technology and no overdrive with a carburetor but I did have an external oil cooler running as low viscosity oil as was available at the time, I think 10W-30 non-synthetic because synthetics were like 3 to 4 times as much as petroleum-based oils and as always we were Not Rich even then.
So, now that we know what’s possible, let’s see what we can do with what we have.