Fuel economy?

[sven557]

I might be getting a 66 c10 longbed, it has a straight six, and I believe it has a 4 speed manual. I don't know too many specifics right now but everything on the truck is stock. This truck is in pretty good shape. Right now it belongs to my grandfather and he's kept it shedded for at least the past thirty years. It runs fine, gas tank has a small hole somewhere near the top, brakes leak, and minor rust; but nothing that is too hard to fix. I'm not planning a total restoration, just fix it up to good running condition and continue to use it as a work truck on the weekends.
I know these old trucks use a lot of gas but I want to know a general baseline for what to expect. How many mpg is normal for this truck?

I've been looking around the forums for a couple weeks now and see alot about swapping out drum brakes for disc brakes. What is the advantage of disc brakes and is it really worth the effort?

Thanks

[lakeroadster]

MPG... not too good. Depends on where you will be driving and what tranny and rear end gear it has. Keep in mind these are heavy trucks. and were geared as such from the factory.

15 mpg is realistic for a stock tuned up stovebolt motor. You could maybe get 19 mpg, maybe even low 20's with some mod's, like an HEI distributor, a newer carb and the right gearing.

As far as disc's go, that also depends on how you are planning to use your truck. The drums work just fine if they are adjusted properly and you are aware that the stopping distance isn't as good with drums vs. discs... and most importantly drive accordingly. If you plan to "hop up the motor" or plan to use the truck as a daily commuter with a lot of stop and go bumper to bumper traffic then disc are a good idea.

Hope this helps

[MacAttack]

John hit all the logic/reality points.

The only thing I'd reiterate is that from a dead stop, these vehicle aren't the most efficient going down the road. Stop & Go driving? Don't even bother trying to calculate - waste of mental resource. Highway? I get about 16-18 mpg with my two-barrel 283 V-8 (new motor), but like the total when I fill the tank - I don't even bother looking after I swipe my credit card.

If knowing what the number was would change the total spent - I'd take note.

Just tune it (and maybe make the suggested upgrades) and just drive it.

Mac.

[driftbuster]

I was wondering about the brakes too. I doubt my old
truck will break 50 mph so I am hoping a downshift or two
otta get me stopped using the Drum Brakes as "backup"!!

[sven557]

I think I can live with drum brakes. I won't be using it as a daily driver; it will get used to haul things and as a back up vehicle if my other is in the shop. 15 mpg on the highway is better than I was expecting! Right now I don't think this truck will go much over 50-55 mph. What is needed to get this truck to run up to 65 mph? Would different gears in the rear diffferential get me there? I doubt I'll be doing a lot of long distance driving with it but it would be nice to go the speed limit.

[Russ65C10]

I orginally had a 66 with the 250 Six and 3 speed, 3.73 rear end the truck would top out at 82 mph MAX down hill with a tail wind. Sounds like you have a lower geared rear end.

You live in Kansas so you don't have to worry about hills, I'd go with 3.73 or higher (maybe 3.23...?) you'll need to swap the entire rear end.

Be thankfully you don't live in CA we have so much crap in our gas that we get like 20% lower mileage than everyone else. I have 65 with a 283 (edelbrock performer 4 barrell, intake and headers) nothing to racy hooked up to a 700R4 and 3.73 rear end. I average like 12 mpg.

And Disc brakes are well worth the cost and effort.

[pestwagon]

John- what is the "right" gearing and which is the "right" carb to use for mileage in a straight 6?

[collins10672]

the highest factory gear you could get in these trucks was a 3.07.with one of these you can run 60-70 miles per hour easily.when you have a 3.73 or 4.11 gear it will hold the truck back.i had a 66 with 283,3 speed and 3.73 with govenors in the factory carter carb and it would get to 75 wide open on the road and when it hit 75 it would start shutting down the engine unless you backed off a little.i also had another 66 with 350,350 turbo and 3.07 rear end and it would cruise easily at 70(actually it would hit 95 no problem,would not do it now im older and hopefully wiser)but really the 3.07 is the best stock axle to have.sometimes they are hard to find though.alot of 67,68,and 69 trucks with factory v8 and automatics had the 3.07.so you might find one in that era truck and remember look at the option list decal in the glovebox on 66 up trucks,if it had a 3.07 it will say so.forgot about the fuel economy part.the best you can do in a stock setup will be a 230(63-65 model)factory i barrel economy carb,3 speed,and 3.07 rear axle it will get about 20 miles per gallon on highway.this combo was offered in the 63-65 trucks.my spec book does not list it when they changed to the 250 6 cylinder in 66.this drivetrain combo was called the economy package back then.my dad had one with this setup(a 64 model)back in the late 70's and early 80's and it got real good gas mileage for a full size truck,turned low rpm's at highway speed,cruise on interstate all day long.also i don't know what kind of gas mileage the factory overdrive trucks got,but it would be hard to find a setup like that since they were rare when new.

[Russ65C10]

My 65 with its 283, 700R4 and 3.73 rear end will cruse all day @ 70 - 75mph turning about 2250 - 2500 rpms and it will bury the stock speedo no problem :-) It'll do it in a hurry too if I drop the tailgate!

You know an other option for Six would be to go with 200R4. It will fit better in the truck, the dementions are about the same as either the powerglide or TH350. Originally I swapped out my Powerglide for TH350 from the junkyard, when it died I first went with a 200R4 because it was the same length as Powerglide and TH350 so I didn't have to mess with my drive shaft. I have "strong" right foot so I ended up having to drop a 700R4 in, it was a tight fit, had to beat down a couple of welds on the cab to get it in plus get a new cross member and shorten my drive shaft.

Even if you have 4.10 rearend an over drive tranny will cruise down the road at a decent speed and reasonable rpms while maintaining the grunt pulling ability you currently have. If it was me, and its not, I'd look at going with an OD transmission either manual or automatic instead of changing out the rear end. BTW you didn't mention if you have a limited-slip rear end or not.

[lakeroadster]

Originally Posted by pestwagon

John- what is the "right" gearing and which is the "right" carb to use for mileage in a straight 6?

I hate to sounds like a broken record, but again I state: Depends on where you will be driving and what tranny and rear end gear it has.

Also depends on how much money you want to spend. The reality is if you pocket the money instead of making the following mod's you could buy a lot of gas....

My "goody" list would read as follows:

HEI distributor: Stock GM type, replacement.

Carb: 4 barrel 390 cfm, Holley (Good mileage if you keep your foot out of the back two barrels) http://www.jegs.com/i/Holley/510/0-8007/10002/-1

Intake: Offenhauser 4 barrell (less restrictive than stock intake, allows engine to breathe better) http://www.jegs.com/i/Offenhauser/750/5416/10002/-1

Header: Flowtech 1-1/2" tube, 2-1/2" collector (less restrictive than original stock cast manifold, allows engine to breathe better)http://www.jegs.com/i/Flowtech/387/11510/10002/-1

Trans: 5 speed from the local salvage yard...http://www.stovebolt.com/ubbthreads/...=595170&page=1

Rear Gear: Pick this based on the engine RPM, trans ratio and tire size. You need a decent "Launch Ratio" for first gear and a decent "Highway Gear" for good mileage.
http://www.5speedtransmissions.com/startlineratio.html
http://www.5speedtransmissions.com/gear_calculator.html

[816allen]

Mines a daily driver 250 I6 3 speed 373 i believe rear i dont want to drive it over 60/65 it sounds like its way to hard on the motor anything more than that... I get on the highway for a lil bit so i get about 13 mpg with no mods.
It will burn oil way faster if i keep getting on the highway ive noticed that...
Well i do have a new exhaust system but thats it.
Headers better muffler and HEI coming soon for sure!

[BMSJaX]

Mine is my daily driver. 350 w/ quadrajet, performance cam, single plane street dominator, HEI, headers and a Muncie 4 speeed with 4.10 rearend. I cruise down the freeway at 70-75 at 3000 RPM and I get around 10-12 MPG city/13-14 highway. And like stated before I dont even look at the pump anymore... I couldn't even tell you how much I paid to fill up last night. I also have drums all around and with the 'Impala Master Cyl/dual line'(about $50 of parts and a days work) upgrade it actually does real well at stopping. Havent had any close calls since I did it.

[Bob66]

You say you have a "small pinhole near the top" gas leak ? Is this because you can see it or you can smell it ? probably just the hose between the plastic filler neck and the tank inlet pipe. This hose is one of my first "replace on general principle " parts for behind the seat gas tanks. I have a metal filler neck, forgot where I bought it though.

All things being equal a 250 is the best mileage maker 6 cylinder as a stock motor for these trucks, but a 292 is mo' fun, and being that your grandad's truck is a '66 'it may be one. You can tell the difference by the side covers, 250 are 4" tall and 292 are 6" tall. A six just naturally pulls a hill better than a V8, and there are headers, intake manifolds, and you can use 307 and 327 pistons and put 1.94 SB valves in the head. A six has bigger and more main bearings than a V8. The rod bearings are huge compared to a small block and each has it's own journal, no sharing. Straight sixes are self balancing, no vibration damper. Check out cliffordperformance.net .

700R4 in front of 3.07 gears economy and warp speed in overdrive. IMHO 200r4 is too weak for high performance or a truck. Six cylinder low end torque handles the wide spread between 1st and 2nd better than a V8. Check out bowtieoverdrives.com .

I have C20 and I just swapped out the entire front crossmember from a pick and pull to get disc brakes, the whole thing hub to hub was $150 out of a t-boned cherry '86, got newer rubber bushings too. If you put front discs on your truck you will need to get a split master cylinder and a proportioning valve so they work right with rear drums. IMHO they are totally worth it, it's kind of important to be able to stop good.

[pestwagon]

FWIW- I checked the gas mileage today on my 66 SWB fleetside 292 4 speed (granny low) all stock single 1 bbl carb truck. Overall, it got 16.5 mpg on freeway, going 60-70 mph (large truck tires in rear) and 3.73.gears (I think, not sure) non posi rear end. But in the city its a different story- only 9 mpg!

[sven557]

You guys are great! Thanks for all the help so far. Bob, you're probably right about the gas leak. I only smell gas, never seen any; but I've never looked very close. I have no idea if the truck has a limited-slip rear. It's a little hard for me to make any decisions when I don't have the truck in front of me yet.

What do all of you guys do as a general principle when you get an old truck? I would guess the only maintenance done to this truck has been the occasional oil change. Would you recommend rebuilding/overhauling the engine?