6 cyl MPG

[rio]

How Many MPG does a 250 6 cyl get? How much more with headers?

[Longhorn Man]

anywhere from 8 MPG to 15=MPG Too many variables to guess, and even if you do get all the variables nailed down, it's still hard to say.
I always say figure 10-12 MPG regardless of engine/tranny/tire size/gear. If you get better, then sweet.
Almost 1/2 of the people who responded get 10 - 12 MPG on this poll from a while back;
http://67-72chevytrucks.com/vboard/s...d.php?t=172346

[Chevy454]

Kinda off topic, but check out this old school MPG test of a 4-cylinder Nova...over 30mpg back in the days before overdrives is pretty impressive! And the auto manufacturers say they've came sooooooo far...!

[rio]

anyone?

[tkeduk8r]

I used to get 15-16 hwy with a 74 250, 3.73's and 31x10.5's... That is with an updated HEI and tuned to the max....
--Mike

[Palf70Step]

My 82 got between 10-12 combo driving. That was with an automatic, pwr steering, AC running and hooked to a 2.76ish rear end.

My 70 with a 3 speed and power nothing, w 3.73s saw about the same, maybe a hair more, if I stayed out of it....but that did not happen very often

[68gmsee]

Originally Posted by Chevy454

Kinda off topic, but check out this old school MPG test of a 4-cylinder Nova...over 30mpg back in the days before overdrives is pretty impressive! And the auto manufacturers say they've came sooooooo far...!

Yeah, I remember... I've been around that long. The problem was they wouldn't pull a hen off a nest... Pintos were no better.

Re: mpg... What everyone is saying about 6 cyl mpg is correct. My 69 had a 250 three speed and no AC before I converted to 350/350 ps and pb. Mpg stayed the same. About 14-15 on the highway and about 8-10 in town.

I did change rear end when I went to the 350. I believe I had a 3.73 or lower and went to a 3.08.

[bad6772]

my 67 250 3speed...Rear gears???????? stock....i get around 12-14....depending on traffic.....

[rio]

I got a Rear axle 307 ratio.How Many MPG.???

[68gmsee]

I didn't know that sixes came with 3.07's.. I always thought they'd be in the higher ratio like 3.73 or 4 point something.... I guess that may get you a little better gas mileage. It all depends on engine condition, traffic, where you will be driving, how you drive, carburetor, on and on...

Everything else being equal, and being that I used to get 14-15 on the highway with a 3.73, maybe your can get 15-16. Hard to say.
But for all practical purposes, expect the worst and if you get better, that's goodness.

[Brad]

I agree with everything that's been mentioned so far. Unless you've rebuilt your L6 and have used quality components and time for the build, don't expect anything more than already mentioned. Your mileage will be a combination of factors with the majority based on city or highway driving and how you drive.

I once put a 3.07 behind my 250/3 speed and regretted it after a few months. You'll use alot more clutch for daily city driving and it gets annoying. Also, if you're using your truck as a truck and hauling loads or towing, you'll reeeeeeally regret the 3.07. If 80% or more of your driving is highway then I definately recommend it.

My engine has about 130,000 on the engine and is could use a rebuild I think to get optimum mileage and performance, but having said that I'm getting about 17mpg @ 65mph

[shifty]

i was getting less than 10mpg, before and after headers, even with a fresh tune. with my 3spd transmission and 3.73 gears, I would wind out on the interstate going 65mph, and was getting 8mp or less.

[rio]

about 77,000 on my engine and run good.

[68gmsee]

Originally Posted by shifty

i was getting less than 10mpg, before and after headers, even with a fresh tune. with my 3spd transmission and 3.73 gears, I would wind out on the interstate going 65mph, and was getting 8mp or less.

Oh, oh... My 68 GMC has the same setup. Completely stock, 250, three speed with 3.73 rear end. I had it on the highway for the first time in several years last week and it sure looked like it was winding high at about the same speed. I'm hoping I can squeeze a little more than 10 mpg out of it though.

[68gmsee]

Originally Posted by rio

about 77,000 on my engine and run good.

If you'll be running it around Brenham you should be okay with the mpg. Not much traffice there and if you go anywhere it's usually going to be highway mileage. I'd like to know what kind of mileage you'd get with that 3.07 rear end.

[rio]

what kind of mileage you'd get with that 3.07 rear end.

[bad_turbo]

I drove my '67 4x4 burb 400 miles on the highway at 55 mph and got 15mpg. It has a stock 250 with a 4 speed trans and 4.56 gears. It has a 1 barrell carb that needs a rebuild, too.

[rio]

anyone else?

[heyjoe]

1967 C-20, stock 250, Rotchester 1 barrel, 3 on the tree, 4:56 rear, no a/c nor power steering.
10 mpg city.

[rio]

anyone else?

[mrein3]

Kinda off topic, kinda not. I had a 1971 Monte Carlo. It had a 273 open rear end, th350, and 350 cu. in. engine with a factory 2bbl. carb. I regularly got 20 mpg and one time in 1989 trekking up to the NW corner of Minnesota to go moose hunting I had a 22 mpg tank followed by a 23 mpg tank. Or maye it was 23 followed by a 22. (They say memory is the first thing to go)

Numbers a touch less than that in a truck are possible but you have to be going down the slab at a constant, slower speed. If you all remember, in 1989 the speed limit was 55mph. As a college student with all the money I had tied up in that moose tag I couldn't afford a speeding ticket so I doubt I was going much if any over 60.

Stop and go kills mileage. A heavy truck kills mileage. 3.73 or 4.11 gears kills mileage. If all you want to do is sip gas down the slab you can build a vehicle that does that well. That 71 Monte I had couldn't spin the tires off the line on a bet but if I was at highway speed and kicked that th350 down a gear - OH MAN!

If all you want to do is make clouds of tire smoke and impress your buddies - you ain't gonna get good gas mileage.

[fishingjred73]

68, 3 on the tree, no ps, or a/c, 3.73 gears get about 13 mpg city or highway. Top speed of 70 with a tailwind

[TP from Cntl PA]

Can't speak for everyone, but my mpg's went up with a set of headers, intake, and 4 barrel..........

[rio]

anyone else?

[jgrh64]

Originally Posted by TP from Cntl PA

Can't speak for everyone, but my mpg's went up with a set of headers, intake, and 4 barrel..........

1st rule of engines "the better it breathes the more efficient it is" imports have known this for awhile they get more power and mileage out of there straight sixes.