Mileage?

[Kixwy2]

MPG 12-16? New engine, so TBD - old engine: 8-10
ENGINE 350 GM Crate - 260hp with 350ft/lbs torque, carbed, with 30 miles on it
TRANSMISSION 350
REAR RATIO 3.08
2WD/4WD 2wd
YEAR OF TRUCK 1974 GMC
DRIVING STYLE mostly normal, until I get on campus and a student jaywalks in my way and makes me late to work = bat out of hell

[Ivan D.]

MPG: steady 19-20, calculated by topping off the tank before and after 150-mile round trips
ENGINE: 350, lightly-ported heads, Offenhauser split-port intake, Holley 650cfm spreadbore double-pumper
TRANSMISSION: TH350 with a shift kit
REAR RATIO: 3.08, but with 33" tires
2WD/4WD: 2wd, but with tires you usually see on 4wd trucks
YEAR OF TRUCK: 1979
DRIVING STYLE: freeway, steady at 2000rpm, about 60-65mph

Reason for good fuel economy - small primary runners of intake and small primary bores in carb make for very high air speed thus better cylinder filling and better fuel atomization. Oh, and about three months of weekend fiddling with jets and power valves and such. Same setup over the winter nets 15-16mpg, only now we're running two steps larger primary jets, keep it in 2nd, and driving through a raging snow storm

[gchemist]

Originally Posted by 79Silv4x4

No biggie--I still love these trucks!

Me too. I tell everyone. Buy a $15 vacuum guage. Connect it to the carb. Use this simple tuning guide. http://www.centuryperformance.com/vacuum.asp
There is more to tuning a carb, but for a novice mechanic it works great!! I use the vacuum guage on my 1406 Edelbrock. Average about 13-14 in the city, 3rd gear and 1800 RPM lockup.

I have no idea what the new ZZ4 will put out. It may take some time before I learn to keep my foot out it!!

[benoit454]

mpg 13
I got this from going 65 miles on the highway and using half tank of fuel or 5 gallons.5 goes into 65 13 times. 13mpg
th350 stock
2.73 rear lockin diff. which is stock
stock 305 with quadrajet that's not really working well.

It's in an 84 c10 2wd short bed with 255/60 15 tires

[Thumpin455]

I dunno what the 454 gets for mileage in the 76. I do know it drank gas like a camel at the only watering hole in the Sahara when it was in the 87 3/4 ton. 16 gallons to go 40 miles isnt good by any stretch.

What I can do is make some changes, rebuild the Qjet, and get everything working right, tune it, and see what it gets for mileage this summer. See how much I can squeeze out of a smogger 454 and 3.73 gears. I would do it now, but its cold out there, I am trying to pay off the bill on my 'race' engine repair, and still keep the house warm. But around May or June I can get plates for it, swap the cam, springs, and intake, then drive it for a while and see what it gets..

and of course let all of you know what works and what doesnt.

[piecesparts]

During the Seventies (the first real bad era of car mileage and high price gas) GM installed vacuum gauges in a lot of cars. The gauges read out in large words like POOR, FAIR, GOOD, OR ECONOMY. This was to let the driver see how he was driving and adjust his mind to a lighter foot on the go pedal. The article above on adjusting the carb with a vacuum gauge is the real deal and it works, but one could go another step further and attach a vacuum gauge to the intake and read his performance on the open road.

[PhilaTruck]

Originally Posted by gchemist

Me too. I tell everyone. Buy a $15 vacuum guage. Connect it to the carb. Use this simple tuning guide. http://www.centuryperformance.com/vacuum.asp
There is more to tuning a carb, but

This is a great resource for the novice like me.

If anyone wants a PDF of this page, PM me & I'll email it to you. I'd post it, but it's too big (240K).

Sorry, almost forgot-

MPG:

low 20s hwy (Driving like a granny, not mine tho' she's got a lead foot.)
305
700R4
2WD
2.73:1
83 LWB

17 hwy (Easy, easy on the gas)
brand new 406
the rest is the same.

Now, with mods to stock Q-jet carb, I think it's less, but haven't checked.

[Rollie396]

Interesting,99% small blocks so far.Where are all the BBs?
They may not be practical DDs but I'd like to see some numbers...maybe we just don't want to know?

[Ivan D.]

You want a big block? How about my '69 high-compression 429, in a lifted longbed 4x4 on 35s it gets about 10mpg city and like 15 or so freeway at about 50mph. Yeah, it ain't no GM engine, but tis bone-stock, miles unknown... a 454 rebuilt with daily driver duty in mind should be able to pull similar numbers, especially in a 2wd truck.

[Ivan D.]

Originally Posted by 79Silv4x4

I HATE these mpg threads. Everyone wants to claim better mpg than the newer trucks that have fuel injection, OD, computers, etc. Please don't insult me--18mpg out of one of these bricks (especially with a carb)? Maybe, possibly, on a downhill run with a tail wind. . .

Last time I checked my 20 years old 4500lb aerodynamically-challenged landyacht rolling on studded offroad tires gets about 24-25mpg freeway, which is more than what many V6 engines are advertised at - tis all about how you tune it and how you drive it. My Chevy had a vacuum gauge in it, that's what I used when driving uphills and such - that, the tach, and the slapstick. I also spent tons of time making sure the carb works at its best, and really my whole engine was set up as a low-revv stump-puller. The fact none of your 15+ trucks never got that fuel economy don't mean tis impossible. Of course I highly doubt I'll be able to duplicate the results on a different 350, every engine is different.