Projects Trying to squeeze a little more gas mileage from a 235

I have a 57 truck 235 in my 37 Chevy p/u with a T-5 and 3.55 gears,working on getting the speedometer more accurate so I can get the actual mileage but it seems like it started using more gas when I slowed down the engine. Played with the jet and put a weaker power valve spring in the Rochester B and it helped but would think a six would do better then what its doing now,I am thinking that motor was designed to be screaming going down the road and probably not much I can do and I thought I was told that GM changed the cam in 59 for more low end torque so maybe a 59 to 62 car engine might be a better starting point and I do have one.

 

good luck bump.......

 

I do not think they were designed for gas mileage so it might be a waste of time and money but would like to see if there is anything I can do,it seemed to do better when it had the original 3 speed and 4.10 gears but it might have to be the price I pay to be able to cruise 70 plus on the highways now.

 

Maybe a call to a custom cam grinder for a chat about what you want? Some of those guys are smart about how to accomplish it.

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When I rebuilt that 57 235 I should have talked to someone about a cam but just put in one for a 57 truck that was available,I have a 60 car 235 on the stand and can change a cam quickly.

 

I just finished a 2000 mile road trip in this ‘51. 235 ci, mild cam, HEI, Fenton headers, T5, .86 OD, 3.23 gears.
Averaged 20 mpg while using the A/C most of the time. That includes a lot of mountain passes in Colorado and 75-80 mph on the interstate. I haven’t had a chance to tune the dual carbs yet. I think it’s still a little rich at cruise.
I don’t think that’s too bad.



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Until I get the speedo calibrated I am thinking its only getting 12 to 14 combined highway/side streets,going to work on the speedo next week.

 

One problem with these stock is the low compression. Most people mill a bunch off the head to try and get the compression up. The pistons sit down the cylinders a ways, so I decked the block to bring the pistons up to zero deck. The head gasket provides a nice quench distance for the combustion chamber. I did mill the head a little. I don't remember how much. I measured and figured the compression ratio to be about 9.5:1. With the small quench distance, I can get a little aggressive with the ignition timing without detonation. It really wakes the engine up. I ran it for quite a while with stock intake and exhaust manifolds and a progressive 2bbl carb. It would get 22 on the highway without A/C.

 

I also think that the B isn't that great on fuel. I'm running a Carter YF on my 261 and the mileage seems to improved.

 

If you're like the challenge and your labor is free every things good. If you're going to spend money the payback can be very far down the road. Also remember trucks have the aerodynamics of a brick.

 

I was wondering if a newer carb might help since the original was designed for that motor to be really spinning.

 

Never designed as a fuel efficient engine
But a carter is a better carb
You can try Langdons Webber/Carter carb
Also have heard using duel carb and split manifolds help with mileage

Just remember it will never be fuel efficient like a modern car but with futzing and fiddling you might make it better

 

Just trying to make it a little better,since it seemed to be better with the original 4.10 gears I was thinking about going back since I do have o/d now. I did try a YF but could not get a bog out of it so over the winter I will take a look at it again and next week I am going to get the speedo corrected to see just how it is but I know it drinks gas just like a V8 and I do know its not running rich.

 

A 283 will get almost as good of fuel economy as the 235. and under some conditions better mileage. That's why I prefer the later 250 inline six engines

 

Hi. My 46 Chevy coupe with a 1957 235 bored 0.060, 268 grind cam, reworked valves, headers, dual intake with 2 two bbl Weber carbs gave me 16 MPG at 55 MPH with the original 4:11 gears & 3 on the tree. Changed ring & pinion to a 3:55 and it gave me 20+ MPG at 65 MPH with air conditioning. My original tranny wore out and I got talked into a T350 automatic and installed a 57 Chevy pickup rear end with 3:07 ratio and millage went to 10 MPG. Questioned the shop on this and they came to the decision that the 2500 stall converter was too high & installed an 1800. Did not get to check millage with that change as about 80 miles into first tank of gas I got severely rear ended on the way home. I may decide to repair the coupe at some later time but not it is just parked in my garage. Took some of the insurance money and just purchased a 1950 Plymouth Deluxe with the flathead 6 for another ride and am going thru some safety items on it and should have it on the road next week. Trying to decide whether to move the Vintage Air from the Chevy into the Plymouth or to buy a different AC unit for it.
Be careful on what changes you get talked into.
Jimmie

 

With the stock setup- I am guessing it is unlikely you drove it at sustained speeds above 60- 65 mph
As speed increases the effect of engine rpm on fuel economy becomes progressively less. Aerodynamics and parasitic drag from things like rolling resistance from tires and driveline friction play a larger and larger role in the demise of fuel economy.
So as your cruise speed increases you are fighting an uphill battle to obtain improved fuel economy with so many other factors besides engine rpm working against you.
Matching the peak torque rpm of the engine to a speed a couple hundred rpm below your intended cruise rpm will help you maintain highway speed and keep your engine in the ‘sweet spot’ for maximum efficiency


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That is a great looking Chevy Coupe....under the hood too....very nice build!

Ray

 

Do you have a tonneu cover on the bed?
That can help the air flow at highway speeds

 

The last semi I drove was a 475 HP caterpillar. Computer controlled fuel system. It has a 13 speed and 12th is direct drive. 13th is overdrive. The so called sweet spot was 58 MPH in 12th gear. 7 MPG loaded or empty unless there was headwind or crosswind. Shift into thirteenth and if loaded you had to drive at least 65 and the fuel consumption increased to 4 MPG. I normally drove 58 MPH. Everyone at the company shop was telling me how fast that truck was. They made claims of over 100 MPH. One nite I was in southern ILL. on I57 loaded to 80,000. there is a downgrade 4 miles long. It was 2 AM no traffic and the scales at the bottom where closed. So I decided I would just see how fast it would go. At 82MPH the computer shut down the throttle and turned the Jake Brakes on. and it began slowing down.

 

Take the Rochester B, throw it in the air and shoot at it, and put a Carter YF, put any other carb on there that will fit. That will help a lot.

 

I was thinking about going to a newer carb to see if that would help.

 

What is the original compression? By todays standards it's probably ridiculusly low, and increasing it and getting a good quench should make quite an improvement. The downside it that it requires taking the engine apart and spend time and money on machining parts. Depending on how much you drive, with your cheap gas you might never make the money back in gas savings.

A correctly tuned carburettor is VERY important ofcourse. Using a wide band lambda to tune it may be a big help - it may seem to be correctly adjusted without actually being, the lambda tells you exactly how much fuel you're feeding it, you "just" need to figure out how much you want it to get and how to adjust the carburettor to do that.
A more modern carb may have more refined metering systems, making it more accurate and therefore more consistently adjustable. I know nothing about the carburettor you have or any one you may consider to change to, but a good, easily adjustable (if you can't get the jets etc. it's not adjustable = useless) carburettor in good shape will help. If you understand it and can adjust it correctly, that is - if you can't it won't matter what carb you have.

Don't forget the ignition, that also needs tuning (and the factory specs might not be completely accurate on todays fuel, especially not after other engine modifications). Make sure the advance/retard and vacuum advance works well and gives you the correct ignition timing all the time - if your distributor isn't equipped with these functions you might want to look for a more modern upgrade.

 

The vacumn advance works but probably not in the range for our ethanol laced gas.

 

My 66 GMC I installed a HEI and a later carb. It has a SM 420 Granny 4 speed and 336 rear gears. and tall rear tires It has one of those motor minder vacuum gauges. Ant I pay attention to it. And it don't use much fuel. Ive never bothered to actually calculate the MPG.

 

A plastic spritzer bottle squirting gas down the carb would have better idle metering than the Rochester B "Flooding system"
Try a Holley 1 barrel [#1945] off a mid 80's Ford 200 engine

 

Don’t know guy but my 55 Chevy with the 235 3 speed got about 15 mpg. Split manifold and a 2barrel was it.

 

What about a slight forward rake for aerodynamics like a lot of newer trucks and SUV's have? Adding a front air deflector behind the bumper but forward of the front axle to smooth out some of the turbulence underneath? Maybe in itself not a great increase but with other things maybe it would help.

 

1959 bel air, 235, 3 speed o.d., bone stock, I get 18.5 mpg at 70. not sure of the gear ratio but it's turning about 24 to 2500 rpm, it seems happy there.

 

I think this 235 is not designed to spin so slow and do not have the money to have 4.10 gears put in the 8 inch,will get the speedo corrected and try to get a small tach and see just what RPMs its spinning and go from there. I think I am now getting too used to late models that cruise around 1800 on the highway and think every engine should be able to do it with reasonable gas mileage,

 

My last Chevy pickup (59) had the stock 235 and SM420, but upgraded to 3.55 posi. With a 30x9.50 rear tire, the best I could get out of it was 12 mpg, tuned with a wide band 02 sensor. It was considerably less when I got it. I discovered this a week before selling it, if I had known sooner I would have built a 283 or 327 for it.

Devin