What kind of gas mileage do you get with your 67-72?

[HO455]

Originally Posted by Lancialonnie

This is a frustrating topic for me! I had read the many posts from people getting 15-17 mpg and that was the range I wanted to be in so I could daily drive my 72 fleetside longbed.
I bought a new Blueprint Engines 383, 430 h.p. and had an early 700r4 non-electronic lock-up rebuilt and upgraded. I have 18's and haven't verified but it should be the original 3.07 gearing. Got everything installed with FITech supplying the fuel and started putting on some miles.

First oil change was at just over 600 miles and I've been logging every tank. Mostly around town with some country driving at 60-65 and I was getting just over 7 mpg! Very disappointing to say the least on mileage but wow is it fun to drive! Smooth, great acceleration, sounds great, no issues with performance. H

I purchased a complete MSD ignition system (distro, 6AL, coil) and had an X pipe installed and starting using Drive instead of OD in town. Now I am just over 9 mpg and I did a couple freeway trips at just over 12 mpg. I don't know of anything else to do to get the mileage up.

Don't get me wrong, the truck runs fantastic and it is amazing on the freeway now. With the tired 307 and no OD it was screaming loud at 65 now at 85 it is quiet and just cruises along comfortably.

I've never driven an LS motor so I don't know if I would have been as happy with that option but I'm sure it would have given better gas mileage?

You didn't mention how tall of a tire your running. But conservatively guessing a 27 inch tire you likely are running 14-1500 rpm at 55. I would bet the cam and head combination is not very efficient at that low of an rpm. You might try doing a test run where you don't use overdrive and see if you can get better mileage. The 3.07's with the OD and taller tires are likely dropping the rpm too much and the flow rate on the intake side is too low for efficiency.