The Stovebolt Site Forums The Shop Area General Truck Talk 13m.p.g.

denny (sandwich) posted up some time ago about fuel mileage. this peaked my curiosity so after renovating the tank sending unit, i thought i'd do some "non-destructive testing" to see where my 50, 3/4 ton came in, in comparison to the other folks on this site.

my speedo is off by a few miles per hour, but it is still the best source for my current findings.

looks like i"m in the 13 m.p,g, area. i could tweak the carb some, and look at other methods for improving mileage, but at 13, i'm still getting better results than vehicles built 57 years later.

sad that either we can't evolve beyond antiquated methodologies, or we are just too passive to allow ourselves to accept the poor results from money hungry corporations bent on making the next buck to finance their next indulgence.

I love my truck. The best thing I'll ever have done for her is to have changed out the rear gear ratio. Now with the 4.10, 50 mph is gentle and 60 is sustainable. If the high-speed morons want to see the front of my truck, they can still go around. And then whine about the price of fuel. One day I'll get my speedometer working, or just do a measured run for the hell of it, to calculate fuel economy. But it feels as if it has doubled from the old 5.14 ratio, and now my truck relaxes all the time instead of feeling wound out.

valid points denny, but i'm still sticking with my 50.

as far as not going fast enough, the irrate drivers who pass me just get a smile from me because i know that whatever car of the moment they are driving will be in the junk yard and i'll still be driving around at 45mph and 13mpg.

I have a '64 K10 Suburban, 350, 4 speed, 373 gears and a Holley 4 barrel. The tires are 30X9.50 on 15" rims. Dual exhaust, with 2-1/4" pipes. This summer went out on the interstate with a friend who is a Wyoming Highway Patrolman. I had the speedometer reading a steady 60 mph for about a mile. My friend said that he clocked me at a steady 65 mph.

Filled the truck up and drove 18 miles, on a lightly traveled highway, turned around and drove the same 18 miles back. And refilled the tank. Kept the speedometer reading a steady 60 mph (ie. 65 actual mph) for 32 of the 36 miles. About 40 mph for the first and last 2 miles.

Results: I averaged 14.3 mpg. I was pleased with the results. For a truck that sits as high as this one, is fairly heavy ( compared to a newer Suburban or Tahoe ) and no fuel injection, I felt, that 14+ mpg on the highway, was fairly respectable.

Buffalo gets 14.3 and that's with two extra cylinders. I don't have a dog in this as my rear is 3.73 but if I was running an original rear I would seriously consider swapping for something that would be less of a strain on the engine and better gas mileage. Just my 2 cents...

I'm running a slightly built 283, turbo 350 transmission and Camaro rearend with 2.73 gears. Alot of people don't believe it, but I get my best mileage at 65 mph. I get on the freeway and hold it at 65 and I get 19.5 to 20.5. I have gotten as high as 23, but I had a considerable tail wind that day, so I don't really count that. Driving 55 around here I get about 14 to 15 mpg.

I can get about 14 or so with my 250 around town. On the road it will get 18 or 19 at 55mph, but at 65 or 70 it drops back to 15 or 16.
My 37 is pushing a lot of air at highway speeds, the front windshield is as flat as a barn side!

My '03 Toyota with its 3.4L V6 gets slightly better milage then the '37. Its a whole lot more aerodynamic and weighs about 200 lbs more.
But considering I pieced the old truck together, made my own intake, set up carburators (3 of them) off a different car, and set the tune up as best I could, I say the old engine is pretty good.

I am with PJ on this one. Old designs are not nearly as bad as most think the are or were.

In a head to head test, same speeds and payloads, I bet the old truck will hold its own pretty well!

Joe

I'm with P.J. on this.
I have a 64 with a 350 (not hot rodded-in fact it runs a 2 barrel), 700R4 and a 3.08 from a 71. Doesn't matter if the overdrive is engaged or not 15 to 16 mph. I do believe that in 40 years the auto makers could do much better than that (in a full sized pick up) if they wanted to.
And yes I do enjoy the fact that I have that ear to ear grin while driving mine.

You guys know the rules. This forum is about old Chevys and GMCs. Let's keep this discussion about them. I just deleted posts about Volkswagens, Dodges and newer trucks. If you want to discuss gas mileage of your newer vehicles, you are more than welcome to in "the Greasy Spoon"

Hey cletis, I saved you the trouble of censoring my reply so I just deleted mine to. After all, I did make mention of something other than an old Chevy or GMC in my post!!!! Sorry p.j. for ruining your thread by comparing the Old & the New in the same breath, that must be Taboo here.
I never could tell right from wrong, oh well, it's probably just a phase, maybe I'll grow out of it!

Denny Graham
Sandwich, IL

I think somebody is discussing a newer than 73 truck somewhere on this board, better censor that one too.

Can you say overzealous? I saw that as a comparison between the old and the new, fitting perfectly within general truck talk. But now the point may be lost. I guess everything is black and white here with some (one) of us.

after closer review, it appears that the latest model vehicle mentioned specifically in this thread was a 1964. this clearly falls under the 1972 or older requirements for this section.

references were made to newer cars/trucks/suv's, and some gas mileage information, but as far as i can tell, this fits fine into "general truck talk".

if you feel that it is not appropriate for this section cletis, feel free to move it to the spoon.

sorry you felt compelled to delete your post denny. i don't think it was necessary.

Something else to consider, driving style will also greatly affect gas mileage, no matter what you are driving.

John

i drive like my grandpa, slow and like i have all the time in the world...but be careful john, talk like that will get you (us) banned.


“I'm nobody! Who are you? Are you nobody, too? Then there's a pair of us - don't tell! They'd banish us, you know” emily dickinson

The manufactuerers didn't care, mileage wasn't such a consideration for many years, not as much as getting more power out the engine was concerned anyway. Then the gas crunch hit and everyone went to smaller motors that were supposed to get better milage. Once the crunch was over it was about getting the most oomph while holding to emissions standards which choked the engines to death & lowered thier economy in several cases. Sure there are several overseas companies that made much more efficient engines in the same period, but in this country fuel resources were not a problem so it was about power, not savings.
If you wanted a better engine and weren't opposed to swapping in a newer block (perish the thought!) you can get very powerful yet economical engines to drop in these days. The GM VorTech motors are an overall good engine for that task.

As for methods to improve what you have, there are loads! Rear end gears are a big one, refreshing or totaly rebuilding a motor helps a lot too. The reality is when trying to make an economical engine there are many crossovers with making it more powerful as well. Stay away from max power and look at what makes it burn the fuel better.
Get friendly with your local machinist, you'll be seeing him alot,...
-Biggest fast improvement is strengthening the components where needed (forged vs. cast pistons) and upping your compression. Compression is so low in our old bolts that you lose a lot of potential power from modern fuels. Bump that 7.5:1 up to 8.5:1 and run higher octane, see what that gets ya. Get it up around 9 and your really cookin with gas! Keep in mind this will burn hotter as well, better have the cooling system up to snuff, pretty much a requirment anytime you are looking to boost the performance of an engine.
-IF they are available, changing your cam profile can have a huge effect on power output when combined with other mods, it can also make a serious dent in your fuel consumption. Searching around may turn up folks that are making custom grinds and can tailor one to your engine & needs.
-Modifying your exhaust to fit your driving style will make a big change & I have done this with varying levels of success on several vehicles. Smaller diamter pipes for low RPM, low end power, and larger pipes for highway driving & high end torque (this is where folks with big pipes see MUCH better mileage at speed than in town).
-Right along with the exhaust, intakes and carbs need to be modified to breathe evenly in as well as out and is often what messes up peoples performance when they only change one side of the engine. Port matching the manifolds and head & polishing is not that difficult (may be able to goto larger diamter valves as well), allowing an engine to breathe better. Better for power numbers, but can also assist fuel econmy. A carb thats can be easily tuned to fit your engine is a great thing, is a big reason why Webers work wonders. For the best performance overall, you really cant beat a closed loop fuel injection system. But if you're looking to keep the motor stock looking, your options are pretty limited. Altho, there are a couple aftermarket companies that are hiding TBI's in housings that look like stock Carter 2bbl carbs.
Ignition is another one, timing timing timing! EFI conversions are nice, but being able to tune the timing advance is key. Changing your timing curve can make a lot of difference, but you have to be careful there.

If you wanna see some basic power numbers and can get ahold of it, Desktop Dyno is a simulation program that allows you to change things around to see what change has what effect. I believe they have a few Inline-6 profiles in there, nevermind the loads of V8's. I haven't seen any of the recent versions, might be more useful now for making an all around performer than before, used to be more about how to get the most oomph out of your engine. Still, a pretty neat program just to tinker with, but also an effective tool for pre-planning. Then it's about research and $$ (always the $$, gotta love it!).

I average around 16 mpg with my 1966 C-10. It has the original 283 and a Powerglide. On the highway at a steady 60 mph, it gets closer to 18 mpg. That ain't bad for a 41 year old truck.

In my '65 (the IRWIPI truck) with a 327 and powerglide and 3.73 rear end, I got about 11.2 mpg average going to Kansas City and back. I ran it about 70-75 mph all the way.

I need a 3.08 rear end.

9 to 11. 62-63 wore out 283 with a nasty edelbrock 1406, spinning a wore out 700R4 tranny, into a 76 chevy half ton pickup rear end with an unknown gear ratio... probably around a 3.73 or so.