I'm surprised nobody has mentioned vacuum yet on this thread. One common misconception out there is that lower RPMs are always better for cruising/economy. That is not necessarily true. Ideally you want to run your engine at highest possible vacuum for the speed you are driving. The engine runs most efficiently at its highest vacuum. I started a thread a few years ago called "driving with a vacuum gauge." There was a lot of great info in that post. I'm not savvy enough to post a link to it in this post.
Someone posted the analogy of pedaling a 10 speed bike. At cruising speed you can run it in 5th gear all day long and not get tired. That is a good cruising RPM at the pedals. Shift it into 10th gear and your RPMs drop significantly. Problem is you have to pedal 3 times as hard to keep it at speed. After 10 minutes you are wrecked. You get a similar result what driving your stovebolt. You end up having to press down much farther on the throttle to keep at speed at a lower RPM. More throttle equals move fuel and less vacuum. I found this out when I installed a 3 speed overdrive in my 58 Suburban with 3.90 gears. I was all excited that I could drive around at 65 MPH at 2400 RPMs but couldn't figure out why my mileage didn't increase. I was getting the same MPG as before the overdrive install.
Anyway, I'm really rambling. Check out the vacuum gauge thread for some great info.
Edit. Found the thread but still can't post the link. Search for "How to drive with a vacuum gauge???" in the daily driver forum.
Last edited by Larry_58_Burb; 01/03/2017 11:24 AM.
