1971 chevy c10

[jagwarman]

Hello everyone,
I recently bought a 71 c10. It is fairly hard on fuel mileage. Here is a bit of info on the truck. It has a 1969 z28 302 short block with mid 70's 350 heads , stock intake with a 750 cfm quadrajet. engine rebuilt with 030 pistons and stock cam with cast iron manifolds, th350 trans and 373 gears in the diff. it get 13 mpg on a good hwy driving day around 10 in town. I know I just jump up the rear gears to a 3:07 and put in a 700r4 trans to help with mileage. But here is my question, if I were to replace the intake and carb with a 2 barrel setup like a Rochester 2gc , would it help my gas mileage much? I am not after performance just hwy cruising. I am trying to keep a low budget for now. Where I live I just run a lot of miles. it is 15 miles just to a gas staion and 40 one way to Walmart. The truck keeps flirting with all gas staions. lol Give me any and all thoughts please

[demian5]

Welcome to the boards!

Its a truck, you are right were it should be with everything mentioned.

tune it up good, dial back timing and lighten up your foot. Maybe put some 33" tires on it if its not lowered to give you more with those gears.

Looks like you should get a cheap civic.

[jagwarman]

Your answer is what I was afraid of. I did put a new electronic ignition in it and tuned it up. That got me to the 13mpg. Before it was 10 and 7 in town. BTW I see you have a Healey so do I.

[demian5]

Originally Posted by jagwarman

Your answer is what I was afraid of. I did put a new electronic ignition in it and tuned it up. That got me to the 13mpg. Before it was 10 and 7 in town. BTW I see you have a Healey so do I.

So you are no stranger to poor gas mileage!

[GASoline71]

Never buy a truck for "mileage"

Mine gets around 6... but I built it that way.

Gary

[jagwarman]

Actually the truck is the worst on gas mileage. My Dodge dually gets 23 my jag with a Chevy motor gets 34 and my Healey gets 21 my 72 El Camino gets 19.

[Mike C]

You are going to be limited to about 16 mpg best case scenario with the carb IME. Their are lots of things you can do to improve. BUT, in your case, sell DZ 302 block for big money. Buy wrecked Escalade. Swap 6.2l LS motor and 8L70E into your truck.

Truck is now fast and gets 18 mpg.

[jagwarman]

I hear ya. That block is worth good money and I have thought about it. The truck runs great as it is and I would just be creating myself a lot of work to do the swap. I may just end up changing the rear gears and then to an overdrive. That will probably accomplish what I am looking for.

[Mike C]

Don’t change gears. The OD takes care of that and will improve all around performance. I’m a TH200 4R guy. I hate the 1-2 rpm drop on the TH700R4. Im buying from Exreme Automatics when I swap the 427 in my short step.

If you keep your foot out of it, 4 barrels get better mileage usually because smaller primaries.

What stock cam? I’m assumng a truck cam and not the 30/30 solid lifter which will kill mileage. And the 76cc heads kill some torque which results in needing more throttle.

OD trans best mod ever.

[jagwarman]

I think an overdrive would really help. Should drop rpm' by 4-500. I need to put a tach in it to see what is currently running at. I don't drive it over 60 and most of the time just 55. I am in no big rush to get anywhere. Just enjoy cruising down life's highway.

[engineer_gregh]

Best advise so far, add an overdrive. Do not put in overdrive trans and 3.07 gears, that is a really bad combination. Just my .02 cents.

[jagwarman]

Greg, do you say that because it would make the truck a gutless turd? Lol

[randy.powell]

700R4 (or 200R4) 3:73 rear. Around 1800 RPM at cruise with 30" tall tires. Still won't make her an economy vehicle but we all know that's not why we buy them.
Merry Christmas!
Randy

[rsgt]

At what road speed does everyone's overdrive kick in? My 2000 chevy truck kicks in at 52 mph. With almost all in town driving my overdrive doesn't get much use. That is why I though it wouldn't do me much good to have one in my 72 Chevy truck.

[Mike C]

If you have 3.07 gears in your truck it is an OK cruiser on the road already. But if you go to an OD trans with a 2.74 (TH200 4R) or 3.06 (TH7000R4) first gear with 3.73 rear it will be a BLAST around town with significantly more torque to the wheels. Then the OD kicks in and you can cruise the highway again.

Again, my preference is the TH200 4R with it's better ratio spread and even more OD than the 700.

The primary thing that makes late model vehicles better all around performers more than anything else is more forward speeds with lower first gear and OD top gear. You will be amazed at how much more powerful an old carb'ed 350 will feel with gears and the OD trans.

[jagwarman]

The truck runs like a bat out hell. I have 373 gears currently. I think all the advice here has helped me to decide to do the transmission swap before anything else. I would like to post some pics but I don't know how. It's not pretty it has just all the mechanicals reworked. All new front suspension, lowered 6 inches in the rear 4 inches in the front, power steering added, rebuilt dz302 engine, all new brake components. I just want all mechanicals done before I give into the body work.

[Mike C]

I'm sure there is a FAQ on posting pics, but in a nutshell, get an account to host images. I use Shutterfly. PhotoBucket is a no-no anymore.

You will right click and copy the image address once you have them uploaded. Then start a new thread or respond to a thread. On a line by itself, type [ img ] (just as it appears, brackets and all, without the spaces) and paste the address you copied. Then at the end type [ / img] once again, without the spaces.

Then complete your thread/response and you will have an image posted.

[70 shorty]

The Quadrajet will get better gas mileage than a 2 barrel if you keep your foot out of it. A 3.07 gear and an overdrive will be too low RPM's for a 302. I'd stick with the same rear gears and swap for an OD, or swap to the 3.07's and keep the 3spd tranny. 13mpg is actually decent for the setup you're running currently.

[Alex V.]

The 302 has the shortest stroke of all the small blocks. Chevy probably used it only in a light car with a really high perf top end for a good reason - the short stroke is best suited for an application that begs to be revved high like a Camaro with lots of sport/high perf options, aka the original Z28. Find a video of an original 302/Z28 running a drag pass, driven by someone with the cajones to run it right - it sounds like a chain saw compared to other SBC's. IIRC the 302's redline was something like 7,000 RPM.

More stroke = more torque. Torque is the ingredient most responsible for keeping a vehicle moving at fairly low RPM, which is what you need to have gas mileage and an OD trans. If your block really is an original Z28 302, it's going to be far more valuable to sell, in turn funding the purchase of a 327, 350, 383, LS swap, etc., than to keep in the truck and expect decent gas mileage and good "daily driver" performance out of when it's being used in somewhat the opposite role the engine was designed for: a heavy vehicle that's at its best with a smooth, torquey engine with a meaty mid-range under the hood.

Incidentally, your 3.73's was a common ratio for a lot of the late 60's 1/2 and 3/4 ton trucks, with no OD. The OD of a 4L80E, for instance, drops a 60 MPH engine speed of 2,600 (30" tires) down to 1,950. The OD transmission plus 3.07's are going to drop the bottom out of that combo, to 1,600 RPM which is well below most gas engine's power curve. "Low-end torque" and "exciting top-end horsepower" were opposites until the perfection of variable valve timing and variable intake volume in recent years. The OD ratio in a 4L60E is yet faster than a 4L80, so you see where I'm going...

Just saying, I think you're asking an apple to be an orange by trying to build an economical, smooth cruiser around a 302 with an overdrive.

Incidentally, the Quadrajet is very much a variable CFM carburetor by the nature of how its secondaries work - so the "750" rating doesn't automatically equate to being thirsty. If you tune it right, and set the secondaries so they don't open when you just look at them, most of your driving will be done on the tiny primaries. My '85 1-ton, with a stock 454, TH400, 4.10 gears, and an 800 CFM Q-jet, would get 12.5 MPG in sustained 55-65 MPH highway driving because it was running on those two tiny barrels most of the time. But, when I'm coming around a 30 MPH on-ramp with a 9,000 lb. trailer and ask her for all she's got, put the hammer down, and hear a noise like a leaf blower start up under the hood, I know I've got all 800 CFM's on my side.

[68Stepbed]

Originally Posted by Alex V.

The 302 has the shortest stroke of all the small blocks. Chevy probably used it only in a light car with a really high perf top end for a good reason - the short stroke is best suited for an application that begs to be revved high like a Camaro with lots of sport/high perf options, aka the original Z28. Find a video of an original 302/Z28 running a drag pass, driven by someone with the cajones to run it right - it sounds like a chain saw compared to other SBC's. IIRC the 302's redline was something like 7,000 RPM.

More stroke = more torque. Torque is the ingredient most responsible for keeping a vehicle moving at fairly low RPM, which is what you need to have gas mileage and an OD trans. If your block really is an original Z28 302, it's going to be far more valuable to sell, in turn funding the purchase of a 327, 350, 383, LS swap, etc., than to keep in the truck and expect decent gas mileage and good "daily driver" performance out of when it's being used in somewhat the opposite role the engine was designed for: a heavy vehicle that's at its best with a smooth, torquey engine with a meaty mid-range under the hood.

Incidentally, your 3.73's was a common ratio for a lot of the late 60's 1/2 and 3/4 ton trucks, with no OD. The OD of a 4L80E, for instance, drops a 60 MPH engine speed of 2,600 (30" tires) down to 1,950. The OD transmission plus 3.07's are going to drop the bottom out of that combo, to 1,600 RPM which is well below most gas engine's power curve. "Low-end torque" and "exciting top-end horsepower" were opposites until the perfection of variable valve timing and variable intake volume in recent years. The OD ratio in a 4L60E is yet faster than a 4L80, so you see where I'm going...

Just saying, I think you're asking an apple to be an orange by trying to build an economical, smooth cruiser around a 302 with an overdrive.

Incidentally, the Quadrajet is very much a variable CFM carburetor by the nature of how its secondaries work - so the "750" rating doesn't automatically equate to being thirsty. If you tune it right, and set the secondaries so they don't open when you just look at them, most of your driving will be done on the tiny primaries. My '85 1-ton, with a stock 454, TH400, 4.10 gears, and an 800 CFM Q-jet, would get 12.5 MPG in sustained 55-65 MPH highway driving because it was running on those two tiny barrels most of the time. But, when I'm coming around a 30 MPH on-ramp with a 9,000 lb. trailer and ask her for all she's got, put the hammer down, and hear a noise like a leaf blower start up under the hood, I know I've got all 800 CFM's on my side.

I'm glad I didn't have to type all that.

[bbrriiaann1973]

I have a 383/700R4 in my 1970 c10 and to honest I top it off with gas when ever the fuel gauge says so! I don't even pay attention to it! I didn't build my truck for fuel economy.