The Stovebolt Site Forums The Shop Area Engine Shop 1954 Chevy 3800 series gas mileage

Hi guys,

Up for discussion is GAS MILEAGE at a $1.65 plus, has me wondering if there is anything I can do?

I have a 1954 Chevy 3800 series (1 ton) with a 235 engine and four speed. What kind of mileage should I be looking for? I was hoping for around 12 to 15 miles per gallon, but I probably have VERY high hopes.

I don't know what ratio is in the rear end, it has a single speed rear axel with 18 inch duals. The carb is the orignial Rockchester type.

Is there anything I can do to improve the performance and get better mileage and keeping the 235 engine? The engine is tuned at top notch running performace. I know this was designed to be a work truck and it has plenty of power, but I have to wonder what it's going to do at higher speeds.

Any thoughts on what else I can do? No, changing over the engine is not an option. I just love the way that little 235 starts, runs and sounds.

John

If it has a open drive shaft you might have a few options,a late model 5 speed o/d trans or check with gear vendors or US gear and see if a o/d unit could be added to the back of your original trans. I know the gear vendors o/d units are not cheap,you would have to drive it alot to get back what it costs. The rearend center section might be able to be swaped with a newer one to get a better ratio,I know gas is getting expensive but that is not a truck that will get light truck gas mileage.

I posted a while ago about using a three speed aux trans, see my post:

12 Speed One Ton

Then click on the link for the Spicer 5831-B Auxiliary Transmission .

Also see my truck webpage for a bit more and a gearing chart for me truck.

Jolly\'s 1965 GMC One Ton .

I'd give some thought to the 2-barrel progressive carb conversion, from Langdon. I was planning that for my 3/4 ton until events overtook me, but that's another story. The
small primary, plus overall better design, should produce mileage imprevement.

If you're on a real budget, figure out how to rejet that Rochester. Carbs can be way rich and give few signs of it; the only way to really dial in is to get it too lean and then back off.

I'd think you could squeeze 12 MPG at least out of an old truck. And of course taller tires is a cheap trick.... if you can find them.

Good luck!
George

Another possibility that I haven't tried on a six is to recurve the ignition advance to give more advance at speed, igniting the fuel earlier, allowing a more complete burn and somewhat better milage. On my 350 it made a 10% improvement in mpg. I know the old hot-rodders did it, but don't know what it would take for new weights and springs on the six.

The rear gear swap is the most bang for your buck, you probably have a 5.14 or so gear now, going to a 4.10 would be a 20% difference in rpm.

I had my 'b' carb set up with a 62 main jet and a power valve restriction that was too big. I had scavenged the carb off a 250. After running way too rich for a while and only getting about 10 mpg I re- jetted it and put the right power valve assembly in it from a scrap carb. Now I get about 18 mpg in the city (mostly 35-45mph roads) with a #57 main jet. My truck is a 1/2 ton with a '62 261, single exhaust with glasspack, 4 speed, 4.11 gears, and 27" rolling diameter radial tires. I was getting about 20 mpg with the 216, but I was babying it because the bearings were so loose. I like to romp on the 261. Also check that your air cleaner isn't restricted. I had a 'hot rod' air cleaner on mine, and it was so restrictive I stacked another element on top of it and extended the center bolt to get enough air flow. That really helped.
You might try a step leaner on the jetting and a lower restriction exhaust, and make sure your carb heat riser flap is working correctly. Also, check your valve lash settings. I like to run mine slightly on the loose side. It keeps the seats sealing well and helps compression. I let my BMW valves get too tight and was getting a check engine light, and after I adjusted them the cel went away and I got about 3 more mpg.

Fred: Going from the 5.14:1 rear gears that are in there now down to a 4.11 rear gear ('67-'72 GM 3/4 ton w/automatic and coil springs) will yield a 25.06% improvement...not just 20%. It's significant for sure.

I am getting 15 mpg on my 3/4 ton truck pretty consistently and would think that you should be right in there with everything properly balanced. My '54 one ton is a HydraMatic so it's a different animal entirely.

I think your mileage expectations are realistic and very attainable. Obviously, the duals on the back end are going to cut into your mileage some. Bucking up the tire size will help but how important is mileage to you? You can play with a number of factors as suggested above but as you make those final tweaks for mileage you begin to compromise performance.

5.14 would be the standard rear end on that truck out of the factory.

Hey guys,

These are ALL some real good ideas, I was thinking about the "advance curve" last night just before going to bed. Then I came up with another thought. You know those really dumb ideas that come to you when your half asleep?

Would it and could it be possible one installing an electronic ignition distributor, with an H.E.I. (I think is called) Thinking back to the late 70's and early 80's six cylinders. I don't know what gear would be used on it, but I am a machinist and I could make something if needed be. I am alomst sure I would probably have to take this new dist. and modify the housing body either bush it up or turn it down to fit my 235 dist, hole. This is just a thought. Has anyone ever tired this before? More than likely there is already somthing on the market to drop on in. I know that I can buy an electronic ignition distributor for my Model A **** , so as many 216 and 235's and so forth engines still out there, there is probably someplace that makes em.

I remember when I had a 3/4 ton GMC (been at least a 100 years ago) with a 454 big block and again dual rear wheels and I had installed this little module kit that mounted inside the cab for the electronic ignition and you could swith (I'm assuming) the "curve" of the spark by changing the switch on the module. It's been so long since I had that truck, I really can't remember exactly how it worked, or even what it was called but I know one thing it made about 5 miles on the gallon. If I remember right, you would keep hitting this swith and when the led turned green, that was top performace.

I was 19 and that truck got a 5 miles per gallon, I did everything and everything to get better mileage.

I have thought about bigger tires, but I have been buying new 700 X 18 original tires a couple at a time, I think the wife would KILL me if I told her I needed new bigger tires, lol. The rejetting is another idea, but everytime I tired that on my Harley, I went from bad to worst. Since some of you have already tired that and with success, I will keep those jets number and keep it with all my paper work on this truck.

Ask Chip about HEI units in 235's. He could write book... :rolleyes: well, I guess he already has.

The problem with judging your truck's performance by m.p.g. is just that... miles per gallon of fuel burnt. My Zenith single-barrel is about as "adjustable" as garden hose, and I need to pull hills with a load; I can't change the fuel mix or timing too much. Until you get some longer legs under it, it will always be slow and thirsty. I had Randy's R&P shove 4.10's in it and without even adjusting the carb I'm well into double digits.

Hey John , just a little over 2 wweeks ago, I installed a 4:10/11 3rd member in my '54 3800 panel. I was driving on the frontage roads at a speed of 50mph, now that I've changed the rearend she will top in at 72mph, and that's with 7.50x17 12ply tires and the old 3 speed with the granny gear. I filled up on fuel last night and in the next day or so should fill up again and when I do, I'll tell you what kind of mileage I get.

tony'n weatherford(TEXAS that is) :rolleyes:

Many have adapted the HEI from the 75 & on six to the 235. Shorten the shaft and adapt the clamp, Tony (from NY) does it with a grinder, but he's an old bike hacker. Here in Kansas the used HEIs are getting scarce, last one I saw they wanted $65 for. Another option is to put a Pertronix ignition in your distributor. Works good if your distributor isn't worn out. Roughly $80 for the module.

As I said, the rear gear change is the most bang for your buck. Last price I was quoted on a 4.10 pumpkin was $75. Find one from a 64-72 3/4 ton. If you search the archives you'll find a lot of good info on both subjects.

One thing that is often over looked is the carb base gasket. The small hole on the mounting flange has to be exposod to manifold vacuum or the power valve will stay open all the time. Most replacment gaskets cover that hole. If covered you can loose about 5 miles a gallon.