improving fuel milage question

[landon4421]

Hello everyone !

I was wondering what I can do to improve the fuel milage in Jenna's 71 C-10. But I was also wondering how to figure out my fuel mileage now. It is 33 miles from home to work, and it takes a 1/4 of a tank to get to work from home? Is that normal?

But as far as the fuel mileage issue. Her truck is a run around town and a back up goto work truck. We use it to go camping and it pulls a trailer. < 1972 c-10 long bed & frame, trailer > The truck has a new crate 350, 15,000 miles. It has a edelbrock preformer intake and 600CFM preformer carburetor. Also has HEI. The transmission is the stock auto, and the gears in the rear I have no clue. I will be looking soon, mabe this weekend.

My question is if I take the 4 barrel off and put a 2 barrel on the engine, will the truck still pull the trailer? Will it improve the fuel mileage? If I chance the gear ratio in the rear, will that work? Or mabe a different transmission? I did not ask the guy we bought the truck from if the transmission had ever been rebuilt? Could the tranny have anything to do with the fuel milage?

Anyway I have rambled enough. Thanks Landon

[JimKshortstep4x4]

The best way to figure your gas mileage is to record your mileage
when you fill your tank. Gas gauges are not terribly accurate. It sounds like your mileage is not very good.

Some things to consider are engine tune, carb jetting, (2 bbl might be worse than 4 bbl, depends on how you drive it), tires/tire pressure, rear end ratio, transmission, etc.

I would suggest looking at 68 Suburbans thread as he is doing quite well with his Burb.

Jim

[bpmcgee]

Landon,

My understanding is that 4-barrel quadrajets well tuned will probably give you BETTER mileage than a 2-barrel because the power is available when you accelerate, but it runs mostly with the secondaries closed.

Brian

[dabeers]

I didn't think anybody drove these trucks for fuel economy anyway.

[jku72]

The only way to have it all, towing power as well as highway mileage, is adding more gears. That means either an aftermarket overdrive or a different overdrive transmission.
You can do some things to improve mileage somewhat, like a hot well tuned ignition, and synthetic oils, but gears is where the glory is. I dont know what crate 350 you have, but if its a thrift master or whatever its called, it has a lousy 8.5 compression ratio. That means marginal fuel efficientcy.

Gears, my dear Watson, gears.

These trucks are capable of better mileage than new trucks, if you are interested.

What transmission do you have? If you have the 4 speed granny tranny then you could step up to a 3.07 rear gear, if the trailers not too big. The low first gear makes up for a tall rear gear.

[Woody]

Landon,
There are a few things you can do to help with gas mileage. Start with the simple things then decide the trade offs on the more costly items.

The first thing I would do is Tune the carb. If you have a hard time staying out of the secondaries, concider unhooking them for around town and rehooking them when you plan on towing.

Next a HEI, but you have one, Tune the timing as high as it will run without pinging. Tune up the engine: New plugs, wires, if needed. try tuning it as per GMC Paul's Vacuume tuning procedure.

Air up the tires to max or close to max running pressure.

Make sure you brakes aren't draging.

Change your rear diff. fluid to a synthic (Mobal 1). Repack your front bearing with a syn grease.

Mirrors? I have the JR RV mirrors I know that they catch a lot of air. Changing to a set of sport mirrors would have to help.

Now things start to cost more but with the cost of gas some will pay back over time.

First what gear is you rearend? The Guys getting 17-20 mpg are running 3.08's (for the most part), these are fine for road running but sorta high for towing. Something around a 3.42--3.54 are nice in between gears. 3.73's are OK but at this point you start needing a 4 speed automatic to (700r4) to get good mileage.

Change your Engine and tranny fluid to synthic. This is costly but helps. With the tranny fluid you don't change it often so the the pay back might be there.

Concider a 4 speed over-drive trany. Cost is usally ~$800-1200 but pay back in a couple years if you drive it a lot. Carefull towing though, make sure you get one built for towing.

This is all I can think of right now. Anyone else care to chime in?

[my67c20]

Lets not forget that the rear spoiler (tailgate) does a great job of decreasing gas mileage. I suggest dropping the tailgate and get a net. Do not run around town with the tailgate down. Nothing worse than getting rear ended by some moron on there cell phone can create a mess of a downed tailgate. If you are towing forget about gas mileage unless you are willing to invest some serious money in new running gear. Ask someone with a newer exploder or suburban what they are getting while towing. Be happy and get a gas card.

[landon4421]

my67c20, took care of the tailgate!:p Put a cover over the bed. it also keeps the line-x looking new.

JimKshortstep4x4, bpmcgee, dabeers, jku72, Woody, thanks for all the input.

Anyone have anymore suggestions?

[68 Suburban]

Originally posted by dabeers
I didn't think anybody drove these trucks for fuel economy anyway.

Some people get off on how fast they go down the 1/4 mile. I drive my burb over 35,000 miles a year, and I love to see what type of mileage I get

[landon4421]

heres a pic of the only trailer this truck will ever pull.

[jku72]

Well, look at it this way. A used set of 3.07 gears can be had for 150 bucks, less if you shop, and if you get lucky, swap your 3.73's to a hot rodde3r, and make them pay you!!!!
You'll get a big mpg boost, I promise.

[landon4421]

I have another rear end at the house. I wounder what gears are in that one as well. I will have to look into that next weekend. Thanks or the idea, jku72.

[cdowns]

i've been getting about 16.8 with mine running 4:11 rear and a 2004r tranny, biggest boost i saw was when i changed to MOBIL1 oil and a K&N air filter. i figure i'll get 20mpg when i get around to replacing the 4:11's with something around 3:20

[cleatussnow]

I too love to play the fuel mileage game...

However I love my 454 and my 6" lift with the mud tires and the 411 Gears so those will have to stay but I still will play.

I have a (695?) quad-ra-puke that if I stay in the primaries and drive like an old lady I have gotten 11. Anyway last weekend was a new tune up and now (in just half a tank, some hot-rodding some slow cruzing) I am seeing 10ish. I think when I do a whole tank on an even cuuze I should get 13-14ish

Cleatus.

[Ackattack]

You could do a few more things...but they start getting expensive.

Fuel Injection my friend. I think for a towing application, the tpi off of a late 80s/early 90s camaro or corvette makes great lowend torque, and then a matching overdrive transmission. I'd guess this would be a pretty good combo for towing and fun to drive.

[jayssunm]

I am kinda slow and don't know much about engines but...

Are you guys telling me my 1967 Shortbed Fleetside truck can get around 17 mpg if I do these things:

tranny with overdrive (200 or 700R4)
rear end gears (like 3.08)
synthetic gear oil (tranny, rear end)
stop doing burnouts at ever green light (this one will be hard!!)

Did not really follow the advance ping thing of the engine. But if I do these things I can stop getting 9 mpg and actually drive my truck?

How tall of a tire should I run in the back? Would 30 inches work??

Thanks,
Jay

[landon4421]

Well I started to keep track of the milage on Jenna's 71. I had stated in the 1st post that I was getting crappy fuel milage. I noticed a great inprovement driving at the speed limit. As well I have keep my foot off the frame rail at every green light.

no more I guess it is time to really drive like a old lady. I will let you guys know how it goes in a few days.

[jku72]

Jayssum,

If you have an overdrive trans, then you can keep deeper gears, if you are poor like me, then 3.08 is the ticket. Free flowing exhaust, and tune the thing.
I have 31" rear tires.

[deerecat]

One more thing to consider that has helped my 72 K20 4x4, with a 350, quadrajet, 4 speed manual & 4.10 gears, is on the highway instead of driving my usual 65-70 mph drop it down to 55 or 60. It doesn't sound like it would change much but I went from 9 mpg to 12-13 mpg. But I do like get places quicker too!!