Let me repeat that, Um, Er, I hate to [censored] people off, so don't be offended but……………I think anyone that believes that they are getting better then 17 or 18 miles pre gallon of gas MAX with a 235 or a 216 Stovebolt Six needs to review his or her math skills.
Fuel mileage has ALWAYS been at the top of the list when it comes to selling hype. GM would have posted the highest ratings they could have to sell more vehicles. And the hundreds of engineers that spent litterally hundreds of thousands of hours developing and testing the Stovebolt six would have maximized every means to get the most out of these engines and still have them last for 60 or 70,000 miles.
The Chevrolet Truck Data Books for Chevrolet Salesmen has a section in the back called “Certified Performance Proofs” where they present numerous examples of the fuel performance based on actual usage. The absolute tops that any of the light trucks reported is 18.05mpg with the average being 15.15 mpg.
After having my stock 1950, 3600 216, w/4sp and a 4.10 gear for about five years and keeping very meticulous records of the mileage and tuning touch-ups about every 500 miles my averages run between 14 to 15 mpg. The engine has 50k miles on it, my compression is within the factory specs, I did do a valve job on the engine when I brought it home because of a burnt exhaust valve. The oil scrapers were worn some so I did have to add oil periodically between oil changes.
Since the entire drive line has been rebuilt and the top end of the engine is back to snuff, the only thing left is the bottom end. So last fall as the bad weather set in I sent the short block out to be completely rebuilt. This year the entire running gear of the truck will be factory fresh from the tires that touch the ground right back up to the carburetor where it all starts. What am I expecting to get for fuel mileage with the entire mechanical portion of the truck in new condition??? Realistically I’m expecting between 15-17 mpg on the hi-way unloaded and 14 -15 mpg around town. So that’s been my experience and I’ve got the log book to back it up for the last 8,000 miles.
As far as the fuel mileage increase by being able to travel at 65-75 mph, these old trucks are not of the most aerodynamic shape and they create a LOT of drag. Energy required per unit distance is roughly proportional to the square of speed when you talking about air resistance. Parasitic drag is subject to the inverse square law and it takes a good amount of throttle to maintain enough power at those speeds, which translates to poorer fuel economy. It’s indisputable that you will get the best fuel mileage with any vehicle at between 25-35 mph simply because of the drag that has to be overcome at higher speeds.
A 3.90 or 3.55 gear will increase your mileage if you drive at a steady 35 mph but not if your running the express way at 75 or 80 or if your in stop and go city traffic.
So in my opinion if your buying an old six cylinder Chevy expecting to get the same fuel economy as a new high-compression, overhead cam, fuel injected, computer controlled all aluminum (read light) engine, then I believe you will be somewhat disappointed.
Denny Graham
Sandwich, IL
