Increase in gas milage

[Awann99]

My 69 gmc 1500 Long bed. Leafs in the rear. 307 rear end. Year old 350 crate. Quadrajet Th350gets around 12-14mpg. If I switched out the quadrajet for a Holley sniper. Installed a 700r4 different rear end gearing. Probably 3.54. What kind of fuel milage increase would i probably see. I would like to trip in to the goodguys get down next year without killing my wallet in the process. I do not want to LS swap the truck. Any other ideas to increase the gas milage? I also would like to make it be my daily for college (because who wouldn’t love daily driving a c10 ) but the few times I have Commuted in it the gas was too much to keep up with.

[special-K]

That's pretty good mileage. Expect less with a square bore carb. You can spend a lot of gas money trying to get a couple more MPG that you 'might' gain.

[Easttennceeten]

Originally Posted by Awann99

My 69 gmc 1500 Long bed. Leafs in the rear. 307 rear end. Year old 350 crate. Quadrajet Th350gets around 12-14mpg. If I switched out the quadrajet for a Holley sniper. Installed a 700r4 different rear end gearing. Probably 3.54. What kind of fuel milage increase would i probably see. I would like to trip in to the goodguys get down next year without killing my wallet in the process. I do not want to LS swap the truck. Any other ideas to increase the gas milage? I also would like to make it be my daily for college (because who wouldn’t love daily driving a c10 ) but the few times I have Commuted in it the gas was too much to keep up with.

Like stated above, 12-14 mpg is pretty good with these old trucks. Heck that's what my 2012 Ram daily driver gets! You might gain 1-2 mpg by going to a Holley Sniper setup and the 4 speed trans, but you'd have to spend close to $3000 to do it. That's just throwing away dollars to save dimes if you ask me. I'd drive the heck out of it and not sweat over a couple of mpg.

[Aus69c20]

I did the sniper thing and the improvement in mileage was barely noticeable.
Not worth it in my opinion if you’re purely after mileage gains.

[FRCvette]

Originally Posted by Aus69c20

I did the sniper thing and the improvement in mileage was barely noticeable.
Not worth it in my opinion if you’re purely after mileage gains.

Same here. I didn't change gearing still have 3:73.

[Keith Seymore]

Just drive slower.

That's free.

K

[special-K]

^^^ Very good tip right there! I save 2-3 mpg by staying at 65 in my '95 truck w/OD and maybe 1 mpg doing 55-60 in my '72. I have no problem on interstates staying in the right lane. It's a speed limit, not a speed requirement.

Was that Quadrajet fresh when new engine was installed? Can't beat one in proper working order.

[CG]

Originally Posted by special-K

^^^ Very good tip right there! I save 2-3 mpg by staying at 65 in my '95 truck w/OD and maybe 1 mpg doing 55-60 in my '72. I have no problem on interstates staying in the right lane. It's a speed limit, not a speed requirement.

Was that Quadrajet fresh when new engine was installed? Can't beat one in proper working order.

This is kind of interesting. When Im in my other cars or (OT) truck Im in the "fast lane" as soon as I can. When Im in my K20 I stay in the "slow lane". Its more than capable keeping up with the fast cars on the left. Im not even considering gas mileage, I just like driving on the right with my K20. For some reason I never feel rushed when Im driving it =)

[67ChevyRedneck]

You won't see much of anything at all compared to the #'s you posted. The best my truck has ever gotten with the 700R is 17 mpg - 100% highway at 60-65 mph (it's happy zone). It drops to 15 at 70-75 and I only get 11-12mpg most of the time "around town."

I did my 700R swap to get my RPM's down, but I already had a 3.73 rear.

[special-K]

Originally Posted by CG

This is kind of interesting. When Im in my other cars or (OT) truck Im in the "fast lane" as soon as I can. When Im in my K20 I stay in the "slow lane". Its more than capable keeping up with the fast cars on the left. Im not even considering gas mileage, I just like driving on the right with my K20. For some reason I never feel rushed when Im driving it =)

Me too. And I prefer the 2-lanes. It's all about the "to" when driving my '72. You know, point A "to" point B.

[Mike C]

You can buy a LOT of gas for what a gear swap, an OD trans swap and FI costs...

You will most likely never make that up. Do it because you want to. Do it because of the performance increase but don’t think the mileage improvement will pay for that stuff.

[71meangreenc10]

I am running a 3.42 rear gear with a 700R4/350 Edelbrock 600. Around town I get about 11/12. On the interstate or long back roads I can get about 16/17. Its a longbed and I drive it everyday.

There was a lot of cost to get it that way. If I do go FI it will be a Vortec swap. Only way I would add just FI is if it was really cheaper to convert. Carbs are fine if you keep them maintained. I average about 8/10 days between fill ups at about $40 a pop, but I live in a small town. Been through Dover many times..... Shoot me a PM if you want any info on the swaps....

Smitty

[Wrenchbender Ret]

The Q-jet is the best carb for MPG. Make sure it is working right & check the ign. system. Make sure the mechanical advance is not stuck or sticky. Make sure the vacuum advance is good. Experiment with timing settings. If the vacuum advance is not hooked to full manifold vacuum, try it that way. Sometimes little things can add up to 2-4 MPG. increase.
George

[cleszkie]

Schedule your trips so you always have a tailwind

[HO455]

Cleaning it up aerodynamically will help. Lowering my S10 Blazer upped my highway mileage from 18-19 to 21-22. Getting the front air dam down within 6" of the ground makes a difference. Do a search for air dam or spoiler. Switch to smaller mirrors, remove the radio antenna. Put a cover on the bed or remove the tailgate. Put skinny tires on. Get a set of Bonneville disk wheel covers. Think salt flat racer.

[68Gold/white]

12 MPG is good, 14 is great.
I also will ask about the tune of your Quadrajet...If yours is just stock, it's doing quite well. A dial in with Cliff's parts can help, but I would NOT touch your carb in it's current condition.
All the stuff you have to do to install F/I is too much work, and too much $$$
If, you want to tey to gain some MPG, I'd buy another Quadrajet, just like yours, buy a kit and all parts needed from Cliff. He can tailor a carb to your engines exact specific needs, every time, it can make a big difference...Don't touch your current carb!!!

[Coley]

Originally Posted by Awann99

....If I switched out the quadrajet for a Holley sniper. Installed a 700r4 different rear end gearing. Probably 3.54. What kind of fuel mileage increase would i probably see. I would like to trip in to the goodguys get down next year without killing my wallet in the process. ..... the few times I have Commuted in it the gas was too much to keep up with.

Remember that the supposed 'payback' on those upgrades is the difference between what your new improved gas mileage might be vs. the old gas mileage.
....what would that be?....2-5 mpg?

Next, what would those upgrades cost? carb/trans/rear diff?....$1500-2000?

So you have to save that much on the fuel difference to make the numbers work.
So how many miles does $1500-2000 pay for? ....500 gallons of gas?

The odds of seeing that savings quickly show up to pay off the upgrades are slim to zero....respectfully.

Now, if you can afford those upgrades....great, and if you want them to improve the driving experience....great, just don't expect them to help the 'bottom line' costs of the truck much.

In my opinion gas mileage has been an odd and misdirecting marketing system in attempting to establish (or 're-direct') relative vehicle costs...but this has been covered before at length in other threads.

All good
Coley

[special-K]

In the early '70s after the gas crisis you could buy nice comfortable fullsize American cars for a couple hundred dollars. The owners were casting them off to squeeze into Japanese econoboxes that replacement parts cost 4x as much as the American cars. All to save money at the pump and make car payments while we drove cars that cost what one of those payments was, but took more gas to run.

[Average Joe]

All awesome advice.

Like others have said, you are already doing well at 14 mpg. Do not expect a miracle here. I would try and tweak what you have to squeeze the most out of it.

Play with the timing and keep detailed notes. Do one change at a time and chart every fill up. Make sure your odometer/speedometer is correct or find out what percentage it is off by to factor accurate milage.

Consider a clutch fan or electric fan. They are worth a smidge on mpg. Synthetic oil in the diffs to reduce drag. Check the drag on your drum brakes. A cold air intake may help slightly as well, especially in the summer.

Like everyone else said, keep the qjet. Learn about them. Especially the adjustable part throttle circuit. An O2 sensor may be a viable investment as well.

The biggest thing here is driving slower. Keep your speed under 65. Ideally 55-60. HO455 hit the nail on the head with his info on aerodynamics.

You may see a 10-20% increase in mileage with most of your current parts and minimal cash outlay. Which is always good!

[Coley]

...also remember to put the air pressure up in your tires....at or near maximum always for gas mileage.
Running soft can cost you a mile or two per gallon pretty easily with the extra rolling resistance.

....oh yeah, don't forget to wax it.

lol

All good
Coley

[firedemon]

I bought an aem airfuel guage lets you tune what ever carb you got properly with real world real time numbers and you can see each circuit so you know your airflow screws are right jets power valve whatever your setup . I have a holley and tend to drive 55 mostly so I set the airflow screws to give me 13.5 to 14 at idle the main jets give me a nice 12.5 to 13.5 at 55 and I set up the powervalve and secondary's to give me around 10 to 11 when I want to jump on it hard . I gained 5 to 7 mpg over using just a vacume guage . im getting 12 - 14 on a stock 1984 350 turbo 400 trans and 373 rear gears . this summer I plan to play with the timing to see if I can get a few more im greedy that way . oh I found the guage in evil bay for around 200 bucks 5 to 7 mpg will pay for it in no time

[jradford]

I drive my duramax for mileage or my car. These old trucks are just for fun. They were built when gas was .25 a gallon and are an aerodynamic brick. Like others have said just drive it and enjoy. My 72 C20 gets around 12 or so and that's about normal for these things. If you want mileage then go to a newer engine with FI.

[Awann99]

Originally Posted by special-K

In the early '70s after the gas crisis you could buy nice comfortable fullsize American cars for a couple hundred dollars. The owners were casting them off to squeeze into Japanese econoboxes that replacement parts cost 4x as much as the American cars. All to save money at the pump and make car payments while we drove cars that cost what one of those payments was, but took more gas to run.

People have told me to just buy a new car to commute in. But with the car payment added to the monthly bill I would probably be in the same boat. One of the reasons I wanted to put the 700r4 in the truck was to bring the RPMs down so I could hear myself think when I’m doing 60 and I wanted to go to some of the truck shows out west without killing my wallet. When I first got the quad jet I drove 100 miles and got 19 mpg and another 100 miles and got 21. Idk how but it just happened and then it slowly dropped the next few trips and has leveled out around 12-14. The carb was off of a shop truck with the sam set up. The block cracked so I bought the intake and quadrajet from him to replace the md 70’s two barrel that was on the truck because it was getting 5 mpg on a good day and I could’ve find information on tunning them. The most I’ve done to try carb is clean it down and plug a few extra vacuum lines. Thanks for all the info.
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[67chevemall]

I increased my gas mileage by 60 percent.
I take the bus Tuesday Wednesday Thursday
45 mile and hour top speed doesn't hurt either