The Stovebolt Site Forums The Parking Lot '60-'66 Trucks MPG

Hey:

Can anyone tell me how I can get the best MPG out of a 235 with a 3 speed transmission and 3.9 rear end?

Thanks!

Glen

don't haul loads, don't accelerate hard, stay under 40

Bill

I can agree with Red 58 on that but make sure you have good plugs,wires,points and condenser,clean oil in the carb filter if oil bath, or replace the paper filter last but not least a good carb rebuild and proper inflated tires will help in achiving good fuel mileage.
62Blue
Don

Agree with Red. Mine does the best on the gravel freeways.

make sure that you have a decent motor to start with eg; compression. you may want to move to a little higher r/axle ratio; in the 3:4-3:7 range or perhaps a little taller tire
ron

Thanks guys. I'm guessing my gut instinct was right - it kinda sucks for mileage. Perhaps a better question should have been, "What should I actually expect for mileage?"

Glen

Yes but other than the suggestions from the others, you would have to sway from stock and spend some $$$ with a good free flowing exhaust and maybe an after market electronic fuel injection and ignition systems. With those three items together you could pick up as much as 4 to 6 more MPG. However the cost would be high about $3500 to $5000 to do all three.
Along with the increased MPG would come the benefits of more power and better drivability the extra power would allow the use of taller gearing where you could possibly find another couple MPG for another $400 $500 of course.
The first thing to do is to ensure that the base engine is in good condition, no loss of compression no carbon build up exc. Then ensure that it is in the best state of tune possible, plugs wires timing exc.

if you get 12+ mpg city you'll be doing OK, don't expect more than 15 without non-trivial upgrades

Bill

Red, are you sure about your data? I get decent MPG from my 235. Last time I checked when on a road trip I averaged 18 MPG and this included some mountain climbing. Now, I will say that was with a different carb. before it failed on me. The NAPA rebuilt carb get's worse MPG. I ended up rebuilding that one again myself with no improvement in MPG, but it does run good and strong.

Now you have me thinking Red.......I wonder if the jets in the old carb were smaller, or something else was different to increase the MPG. Something for me to investigate...

The carb, timing, & vacuum advance all need to work good to get the best MPG. The only way to increase it if you are doing highway driving is a higher gear ratio. The engine is just turning too fast with the 3.90 gears to get respectable mileage.

Jeff - I did say 'city'- there's always some variation due to the way a person drives of course, and as George points out, there will be variation in the state of tune, even of the same engine over time .... but I'd be very surprised if anyone really gets an accurate 18 average at highway speeds with 3.90's unless it's mostly downhill

Bill

Red, I did notice a big increase in power after I rebuilt the carb, and this was after the road trip when I got 18 MPG. Perhaps I had a fuel restriction and that caused the good milage. I do admit I don't get that kind of milage now after the carb rebuild and tune up. I haven't check the fuel MPG since the carb rebuild either but it seems to suck more gas then it did before.

My last 325/three speed/3.9's was in a '57 3200.
17 MPG City or Freeway on leaded regular.
That truck was comfortable at 55 MPH on the freeway.

Thanks again guys. Anyone tried switching the Rochester carb for something else? Maybe a 1bbl Carter? I've heard the old Rochesters weren't the most efficient.

My experience is a one barrel carb gets miserable MPG. That was in a '70 Nova with a factory GM Monojet on a 230 I6. Great little carb., just not great mileage.

I got better mileage with a 1977 305 with a factory 2 barrel.