Mileage and performance both good and bad, are a function of getting your engine and drive train in balance. Back in the day when gasoline was $.19 a gallon and our trucks were used for work and putzing along on roads that wouldn't support 65-70 mph speeds, the old trucks with their 8-12 mpg consumption, were still pretty economical. However, in their second or even third lives, and with 45-50 mph speeds constituting a "rolling road block" and gas prices nearing $4.00/gallon, regaining that "balance" can put you both up to speed, and give you surprisingly good mileage.
The key is improving on the efficiency of your engine and getting your drivetrain modified for the type of driving you most often you do with your "reborn" ride.
In a world that seems to be driven by the "horsepower game", I've discovered that it's really all about torque. And torque was what these engines were designed and geared to produce. When we take on a resto project we somehow focus on getting all the visual stuff upgraded, but are then disappointed by the fuel mileage. To complete a restoration, which you intend to put on the modern highway, you should also address all the issues that will effect performance.
A common misconception is that dropping your highway rpms will improve fuel mileage, but in reality, it's matching your gearing to your engines torque band and the normal speed you drive. An engine that is lugging at the lower end of the torque band isn't going to provide good fuel economy.
I've based my current fuel consumption (18-20 mpg) on my 54 truck over the past 5000 miles, on getting my 235 tuned and geared to match my particular driving needs. As 55Tractor points out, getting the 14-1 fuel/air ratio is tough with the stock carb and add to that, trying to run the engine at highway speeds with stock gearing, is only going to adversely effect engine performance and longevity.
I've discovered that after a vast number of engine modifications and using a 261 grind cam, the 235 torque band is STILL between 1600-2400 rpms. So based on this observation, I geared accordingly. In my particular case the T5 .72OD, 3.42 R&P with a 28" tall rear tire has produced fairly good performance and fuel mileage. I shot for 2000 rpms at 70 mph. However, I've found that my vacuum readings at a steady speed, will increase as I increase my engine rpms towards 2400. I've also discovered that most of my casual driving is well below 70 mph and that the legal speed limit and those that enforce it, frown on exceeding that limit. So, in my particular case, I need to jump up on my R&P ratio to 3.55 or in my case to 3.73. (Plenty of Camaro 62" wide 3.73 diffs) I seriously doubt that I will gain that much on fuel economy, especially with the E10 blended fuel, but my performance at my now more conservative cruising speed (60-65 mph) will improve or at least hold it's own.
The key is to match your gearing to your driving habits and focus on staying at 1900-2300rpms. That gives you a little cushion below and above should the need arise. It's really amazing what a couple hundred rpms can do to help or hurt your engine efficiency/fuel mileage. And with the reduced mileage from the E10(up to 25%) and the higher cost of fuel, it might be a good time to start paying attention to improving fuel economy.
So folks, crunch the numbers, gear so that you are closer to the top of the torque curve (1900-2400) at your normal cruise speed and you'll be able to enjoy your trucks great performance and save a few bucks at the pump.
Dave
