What kind of fuel mileage is every one getting

[cdowns]

i think the overdrive tranny with those 308's you'll find not so good // you might get 14-15mpg

[eldogg]

I've had a bunch of 73-87's with 355/700r4, 3:42, 28" tire & Q-Jets combos that would get 21-22mpg. Granted they would only get 12-16mpg around town. Maybe it helps that I'm great at tuning a carb?? Just my 2cents.

[mrein3]

Originally Posted by molinehotrod

I have 420 hp, 32 inch rear tire, 3.08 gears, 700r4 with 30% lower first gear and a taller over drive gear, i think it is .67. I think i am going to get 23- 25 miles per gallon.

Think is the key term above. I highly doubt you're getting 23-25 mpg.

The first thing you need to do is take your or a friend's GPS and get it receiving data. Find the screen that has mph or like on mine, "SOG" or speed over ground. Then find a 30 mph zone, get the truck going 30 mph on your speedometer, and record your GPS speed.
Then find a 45 mph zone and do the same.
Then find a 55 zone and do it again.
I bet your speedometer disagrees with your speedo by a long ways.

Once you get your speedometer corrected then figure out your mileage.

To do that is quite simple. Fill your tank full. Write down the odometer reading. Drive like you always do and fill your tank again when you need it. Write down the odometer reading and the fuel you put in.

Subtract reading 1 from reading 2. Take that difference and divide by the amount of fuel you put in the second time.

THAT is what your mpg is. Guessing by what a wrong speedometer (therefore wrong odometer) says or by counting mile markers is

When you get your speedo gears right and figure out your mileage the correct way report back.

FWIW, I get 10. My best ever is 13.4 when I still had a manual transmission and wasn't towing anything.

When I'm planning a trip where a tank full won't get me there I plan on 10 mpg.

I last filled the truck in November. I keep it off the salty roads but do plow my driveway and run it out to the fish house and back. I usually average 4-6 mpg in those conditions. I'll let you know when I fill it up this spring.

[LMN8UR]

I have broke 19 mpg with the old 350 and everyone here thought I was full of then!
Last week I dropped a new 383 (the shop says it should be 400+ HP). Hope it doesn't kill my mpg, but who cares if it's fun! I'll let ya know how it comes out.

[71meangreenc10]

These trucks werent designed to get high mileage, I get about 10-12ish around town with the 350/350 3.08's, my speedo is about five miles off........you might get 20 if everything was made of fiberglass, but again with todays light made trucks and fuel injection they are barely getting 20 and thats after 40+ years of technology and thats a 2wd auto with od......I dont mind the gas cost because there is NO car payment involved.

Smitty

[1quik70]

I ran my 70 LWB with a 350/350 combo & 3.73's and normally got 15-16 on the highway. The carb was very well tuned, and the engine components worked well togther.

[northburb]

The difference between "thinking" and "reality" is all in your mind.....or math in this case.

I think I'm good looking, the reality is... I'm ugly as a picked fence....

If it turns out you are actually getting that kind of milage, please share what your secret is....

I think I get about 8-10 in my burb...( never clocked it, to affraid )

[CE20934]

The econo-boat can get 24-26 if I keep my foot out of it and loaf along at 70. However that's a TBI 305/700-R4/2.73 with 26" tires.

The truck used to get 11-13 when it had a 400 SB. Now it gets 7-9 with the 427. Same trans (SM420), same rear end (4.10), same tires (32"). I'm still tweaking the carb.

I did get 15 once with 30" tires & a 4.57 rear end. The speedo was also reading 20% high.

[Stocker]

mrein3, that's a great post on fuel mileage calculation. I'll add this: for greater accuracy, aside from filling up in exactly the same way every time, use the three-tank rolling average.

It's simple -- combine your three most recent tankfuls. When you fill up, add that one to your calculations and drop your oldest of the previous three. This helps minimize the inconsistencies and give you a more accurate consumption figure.

[mstrav1973]

another thought would be to go on a 100 mile trip with a chase car that is accurate if you dont have the gps. Go about 50 miles and then come back to the same pump at the same station. my rig is a 4x so I would think 2wd would be 13-15 when well tuned.


what do the straight 6's get with a stick?

[LONGHAIR]

Not to "pile-on", because that is not what we need here....But it is faulty thinking that getting the lowest RPM possible at highway speed will net the best fuel mileage. You really need to be in the "sweet spot" of your particular engine. For mostly highway driving and the best economy at that speed, you should probably have a cam and corresponding engine parts that work best at around 2200-2400...and the gearing to keep it there.



In case subtle hints don't work......Play Nice.

[Stano]

fuel mileage? more like fuel footage! lol not really its like average 12-13mpg est with a mild 350 400t 3.73's and 275 60's on the rear. Turnin like 3000 at 70mph

[72chevyk10]

my 4wd 454 gets 13 on the highway with 4.10s and 35's and the t350 trans. im pretty happy with that. i get about 15-16 in town

[eagleuh1]

68 C20 327 Q-jet 4 barrel w/HEI TH400 4.56 with 33 inch tires got 10 to 11 mpg driving 10 miles out and 10 back from work every day. Usually didn't go over 65 because I had to pedal to fast.

[68 longbed]

4.3 v6 quaderjet 4 barrel, wc t5 trans with 308 rear 32 inch tire getting between 18-19 depending on way driven

[big_al_71]

Maybe 9-10 mpg definetly smiling from ear to ear!!!!

[C20-67_N_MO]

Sorry but I am calling this guy out.

Cuz myself I think he is jus trolling because there is no way he is getting this kind of mileage in a 1967-72 series pickup truck!

[John Knight JR.]

I have 1970 4x4 3/4 ton tires are 33x12.5x16.5 gears are 410. With 350and 350 trans. I get 9 if i use 93 oct. Only.

[Jobe72]

Best I can tell...350/350 with 3.08 gears and 30" tires...10-12 mpg

so how big were stock tires?

[eagleuh1]

Don't take the bait and hook so deep then. Sorry.

[KFreddy]

Originally Posted by molinehotrod

I have 420 hp, 32 inch rear tire, 3.08 gears, 700r4 with 30% lower first gear and a taller over drive gear, i think it is .67. I think i am going to get 23- 25 miles per gallon.

Is this a riddle? 'Cause if it is I've got the answer; it's a diesel engine...

['72customdeluxe]

420 horsepower diesel in front of a 700r4 800-900 lb/ft wouldn't play well with even the best built 700's

[1971gmcshortbed]

Originally Posted by '72customdeluxe

420 horsepower diesel in front of a 700r4 800-900 lb/ft wouldn't play well with even the best built 700's

Ahem,

http://www.transmissioncenter.net/700MegaRaptor.htm

[fjthompsoniii]

My 70 2x4 with 3.08 gear 350/350 with stock size tires, when well tuned eeks out about 14.5 mpg. However my 70 camino with mildly built 350/350 combo and a 2.56 gear will get 17-18 if you can keep your foot out of it. It seems like some times a higher horse engine that isnt totally radical will get better.... maybe cause it doesnt have to work as hard?

[tommys69/454]

about six if I stay out of it!!!!! lol