The Stovebolt Site Forums The Parking Lot '60-'66 Trucks Best gas mileage in a 60's Chevy?

From one of my other threads, located at

https://www.stovebolt.com/ubbthread...lat&Number=621699&gonew=1#UNREAD

Justhorsenround has posted "Here is something to think about. Gas mileage depends on how hard the engine is working, right? I can almost guarentee that I can get as good or better mileage from a small block V8 and auto transmission geared for highway usage than the average Joe can get from the 6 and stick. The 6 has to work too hard. Just my 2 cents worth but based on 50 years experience."

What do you guys think? My assumption was a 6-cylinder stick would be the best for gas mileage, but I know nothing about vehicles, especially vintage ones.

What combination of engine, transmission, and other factors would result in the most efficient truck?

i'm sure not saying horsenaround is wrong, but that has not been my experience. if that was the case my 292 would get better milage than my 250 because it doesn't have to work as hard. it does not! noice how he said "geared for highway use and updated". that makes a difference. if you are going to be pulling big loads, consider the bigger engine, he's right it won't have to work as hard- everything else being the same. notice also it was him verses the average joe too- he is going to have it set up right where the average joe is not. and how about the miles on either engine, that's a factor too. i bet if he set up both with same gearing and same tranny, if the six is smaller, it would get better milage. you were looking for a 1/2 ton truck right? the six won't be underpowered if you keep the orig rear. my 64 c20 wrecker pulls over 10,000lbs gvw now and then and can do it fine with a 250, but it has the gearing for it. but whenever i am empty i reap the benifits of better milage than a 350. more than 1/2 of my miles are empty, a 350 would be a waste for me. i might be able to rarely get to the top of a hill without having to downshift less than now when i'm fully loaded. for the most part it wouldn't help me.

I'll concede the average 6 to him. The Austin Healy 3000 is one awesome l6, and the mpg is not bad. Then again you could not shift the Le Mans Healy into 2nd without dropping the engine almost to idle, or break the tires loose. :]. I saw a nice 65 C10 Custom and the owner said he just put a 4bbl on his 250 the mpg went from 11 to 15. It was your average 65 just well taken care of, been in the family since new.

I think what we are talking about is gearing for optimum use.

Larry

Thanks, guys.

Ok, so let's talk about standard options first.

Hoggyrubber, yes, I'm looking for a 1/2-ton stepside shortbed, 1963-1966. And my main driving would be on a highway with speed limits between 45 and 55 and several stop-lights between here and work.

So, standard options:

1) V8 4 on the floor
2) V8 automatic
3) I6 4 on the floor
4) I6 3 on the tree
5) I6 automatic

Then I guess there are a couple different sizes of V8's and I6's.

I've always heard that a manual will get better mpg than an automatic, so I'd guess that neither of the automatics would be the winner here. I've heard that a 4-speed would be better than a 3-speed if the low gear was really usable, not the "3-speed with a granny" style, which I think is what the I6 4-speed would have been. So maybe the 3 on the tree vs. 4 on the floor would be a wash?

And a good 6-cyl should beat an 8? Would a smaller 6-cyl be more efficient than a bigger 6-cyl?

Am I putting too much thought into this?

i don't think the newer automatics are bad, but the older ones had quite a pit of power loss just to drive tranny. the manuals were the most eficent back in the day. if upgrades are not a problem you could run a automatic fine i'm sure. all the originals had 3 speed with granny type or sm420 so no real difference between that and saginaw 3 speed. the final drive ratio is 1:1 i believe unless you install a latter tranny overdrive unit.
i wouldn't say any six would beat a 8 on milage. the style of six for these trucks run 198, 230, 250, and 292. if it's just a empty 1/2 ton it will weigh around 4000lbs. the 230 would be kind of a dog but ok. i think the 250 would be fine. now if you are comparing it to a 283 not a big advantage on milage. seems like everyone wants to drop in a 350 and i would bet the 250 would beat it on milage. now i have not built a 350 and put it in my truck to compare so i can't tell you the exact #'s.
would be interested if anyone has seen a change in milage in swithching from 6 to 8 or back. if both were in comparable shape. i have owened some wore out v8's like a international 352 (i think) that got the milage of a school bus, so you couldn't compare apples to oranges.

I have a 64 with a 350 (stock build), 700R4 and 3:08 Posi. Goodrich all terrain tires (all 4 wheels). About 1800 rpm @ 65 miles/hour. Gets 16 mpg on the highway.
Tried swapping out the 4 barrel for a 2 barrel (stock cast intakes), still 16 mpg on the highway.

Ok, forgive my ignorance here... The 350 is a v8? Also, the 283 is also a v8?

Seems to me that 16 mpg with a 350 is not too bad. It would be nice to get closer to 20.

Thanks.

the 350 is a V8, so is the 283. I have a 283 in my truck, but I don't know the gas mileage...I don't think its very good though. I have the stock 3:90 rear end and a 4 speed with granny low, so I'm not geared for highway use that well

Shortbed, not going to haul a lot of weight, but you can still load it with camping gear and an occasional refrigerator. Not many around, nice little truck.

Automatic your Dad was right then, as hoggyrubber says the newer automatics are much better. The trick is to get a locking converter. I'm not sure on the particulars there, just when does the torque converter lockup and how.

3spd there was a transition in the late 60s from the old 3spd (sm318?) to newer Muncie which has a synchro 1st gear. You don't want any ponys in front of the old 3spd. I got very good at changing the slider gear (2nd&3rd) in an old 3spd behind a 300 hp 327. Both transmissions had over drives, but I believe the later with OD is harder to find. The synchro 3spd was available in passenger cars in 64(?).

Rear axle I don't see any way not to change the rear axle ratio, even with an OD. An OD might be a reason not to change the rear axle, your mpg would take a hit. What rear axle ratio depends on engine, 3.08 to 3.55

Engine, trucks don't have much weight over the rear axle, and a short bed has less. Bigger tires are not the answer to good mpg, there is a limit where they will hurt mpg due to weight. There is not much difference in weight between a 6 and 8 cyl, the 6 is heaver. I'd go with a 250 or 283, not the 292 or bigger v8. I would build to 250 to about 220-250 hp. That would be enough cam for a mild lope, for the stop signs.

The proverbial 2s

Larry

It really all comes down to a balancing act with many variables to consider. Even a short bed step side weighs about 4,000 pounds empty, with the aerodynamics of a brick, and a built in speed brake above the windshield. 20 mpg isn’t unreachable, but it would be easiest to obtain with an automatic overdrive transmission, optimal rear end gearing and electronic fuel injection on whatever engine is selected. The trade off being the cost of the upgrades compared to the savings in better mileage.

What’s most important is setting up each truck to fit the realistic needs of the owner. Years ago my daily driver was a 1954 Chevy 2 door sedan. With a 235 six it got about 10-12 mpg, and after I swapped in a 283 V8 it jumped up to about 16+. Not sure how much of the improvement was mechanical vs driver input. I was much easier on the V8 because it would climb to speed easily (and in the beginning I was still running the break easy stock transmission and torque tube rear end), without shoving the pedal to the floor all the time like I did with the 235. The 235 in this case was a bad fit for me because I wanted a hot rod and the six was a low rpm torque motor.

My current driver is a 1960 GMC short step with a stock 350, Super T10 4 speed, and 4.10 rear axle. Normally this would be a ridiculous combination for a daily driver, but it’s ideal for me because 90% of the time it’s driven at 35 mph, and rarely goes above 50. Last time I checked it was getting about 16-17 mpg. If it were driven on the freeway the mileage would probably drop near single digits.

Personally I like both the six and the V8 for different reasons. The sixes are simple and easy to work on, make a lot of torque, can last forever with almost no maintenance, and are popular at rod runs because they’re not very common anymore. For around town driving they can be ideal, where theoretical mileage may not be all that important if the truck doesn’t rack up a lot of annual mileage.

A modern V8 spins higher, faster and is much easier to tune to lean running, because so many combinations of parts are available compared to six. A small block V8 is physically smaller with a nearly unlimited amount of inexpensive speed parts available.

Any combination of V8, six, automatic or manual transmission can produce an ideal arrangement if it’s suited to the application. If an automatic transmission is chosen, a lock up converter will lower engine speed. A few years back I swapped in the 4 speed manual replacing a Turbo 350. With no other changes, my engine speed dropped 500 rpm in drive by eliminating the torque converter slippage. An overdrive transmission can also eliminate the need for a rear axle change. A .70 overdrive will change a 3.90 rear end ratio to a 2.73, providing potential savings, but it is important to match the final drive ratio with the power curve of the engine. If the engine is running at a speed below where it makes torque, mileage will suffer.

darn, I opened a can of worms didn't I. I still stick to my original statement! It's really easy to top the 20mpg mark if you set the V8 up right. The misconception has always been better mileage with the 6. It just ain't so. If you set the 6 up right, and most don't, you can get close. I'm sure we'll hear more.

No, Justhorsenround, this is great. Thanks for opening that can of worms! This is all good info, even if I am now lost in a sea of numbers (engine sizes, transmissions, and gearings).

So what is your specific setup that allows you to top 20mpg with a V8? What kind of truck, engine, transmission, and gear ratio? Could it be duplicated on a 60-66 truck?

Whatever you have, it must be good and well thought-out. Is it all aftermarket parts and mods? Like someone else said, it might not be worth paying a grand to upgrade a truck to save $10 a year in gas.

283, 327,350 it really doesn't matter. A good rebuild with quality parts. It can be done with carberation or fuel injection. Just a good tune to a good engine. Gearing needs to be high enough to let the engine loaf along (within reason)and for most drivers the automatic transmission will yield the best results. It takes a skilled driver to work the stick shift tranny to its optimim. If you have it put together right and you drive like you have a raw egg under the accelerator most anyone can get the magic 20mpg. Not much science to it just good ole common sense.

i sure see what you are saying about changing the rear gearing. that would be the biggest bost to milage no matter what engine you are running. some v8's would be able to handle the taller gears better and make some of the smaller sixes seem pretty puny and might get better milage to boot. but for how these trucks were originaly built i still doubt a 350 gets better milage than a 250 with everything else the same. yes, if you insist on flooring it at every light and drive 70 down the interstate, maybe your right. my 64 shifts into 4th gear at 25mph and milage seems to be best at 35 to 40. i rarly drive over 52mph. that's what my truck was designed to do and i realize i am in the minority. why would chevrolet keep around these gas hog sixes for all those years after '55? they were always listed as the economy model.

I do like the point that a poorly driven stick might get worse gas mileage than an automatic. I've never driven a stick, so it will be new to me, and I won't be the smoothest stick driver for a while.

However, I do want to be able to do most any work my truck requires. A 6 with a manual transmission seems like the simplest system. That would be worth a lot to me, and still, that setup seems like the best mpg in the stock setup. So I think a medium to large I6 with a stick is still my goal.

However, if I see a cheap V8 truck where everything else is perfect, maybe I should jump on it and consider switching out the rear later on.

So much to learn...

I got the 250 but it's bored out to a 261, 3 on the tree 1/2 ton stepside shortbed, so it's the lightest one possible.

I get 14 mpg drivin normal to school, about half city half highway.

I get 11 mpg if I goose it everywhere i'm going on the way to school, like if i'm running late (which always happens).

Now, for some odd reason I get the best mileage when I'm doing over 80 mph, and with only 3 gears the motors just screamin at this point. I wouldn't expect it but thats my best fuel consumption, go figure..

During mileage testing, my truck attains better mileage numbers with a T10 4 speed, but in daily service the 350 with the slipping converter was probably more efficient because it didn’t rely on driver input. The 4 speed manual is so much fun it inspires less efficient driver behavior.

If you want to learn everything about vintage trucks, a 3 speed standard can easily be rebuilt at home by a novice with a service manual. It’s very empowering being able to fix everything yourself.

Good morning to all.

I read this post with interest because I have a 1980 Vette 350, TH350C (c is for clutch which adds 2 MPG when working) with about 3.08 rear end that I get 20 MPG with if I drive easy and not over 55 -60.

So when I built my 64 1/2 Ton Chevy SB Stepside with a rebuilt 350, Super T10 and 1.56 rear end (yes that is 1.56 from a 1978) I expected to get 20+ GPM. After I learned to drive easy I get 14 MPG at about the same kind of driving. I have an Edlebrock 600 cfm 4bl carb and jetted it down 2 steps and still don't get much better mileage.

Now the vette has a Rochester 4 bl which I am told is the best and is probably the reason for the better mileage. At some point I want to try that on my truck.

How about everyone that has a 15+ MPG combo sound off so we can see what is working?? Truck, engine, carb/inj, trans, rearend.

Thanks,
Ron S

Thanks, everybody.

I agree with Ron regarding people posting their setups and results. Certainly everyone here knows roughly whether they're getting MPG in the low teens or if they're pushing 20.

It would great if the folks with good or great gas mileage would let us know their setups, and it would also be great to hear from those with stock setups. How's it working for you?

Thanks again for everything.
Steve.