toobroketoretire

I have been tinkering with my big block '71 for the last couple of years trying to improve it's fuel mileage. I started off with a dismal 8 mpg and now I'm getting 14 mpg so it has improved a lot.

What kind of fuel mileage to you guys get and what engine/transmission/rear end combination do you have?

JimLentz

10 MPG '77 L-48 with 3.08 rear end and TH350 transmission combined city/highway. Not sure why it is so bad as it runs well otherwise.

terry82

have you replaced factory cat ?

ajrothm

In my 71', I average 9 mpg in the city, 10-11 mpg commuting the freeways, and 12 mpg out on the highway running the tank full to empty at a cruise rpm of 3000 at 70 mph. This is running AC as well. This is a 650hp 496, 850 DP, T400 w/tight 10" converter, 3.36 gears and 28" tires. .

I just took it on a 2700 mile road trip and my total trip average was 11 mpg running the AC the whole time and running the Tail of the Dragon 4 times.

augiedoggy

Im getting closer to 14mpg judging by the roundtrip to my cabin and the amount of gas thats using. (actually its just about the same as the 360 in my lifted pickup with 35" tires and 4.56 gears on the highway) in my 74 with the replacement 355 I built/ this is with a holley avenger 670cfm carb with #72 primary jets and a #37 squirter, sidepipes th400 and 3.08 gears.

mrvette

Years ago my L48 with L98 induction FI on it, stick shift 4 speed Muncie, and 336 gears got 24 mpg between Md. and Fl.....18 years ago when shopping for a house down here......

Today with the 200 4r auto same 336 gears, I dunno what the car gets.....why?? because I live about a mile one way to most anything I need from car parts/banks/food/fast food/ gas stations....18 gallons will last me about 1.5 months..... obviously retired age 71

MotorHead

My 600HP 427ci small block gets 22-24mpg on the highway and about 15-17mpg around town. I run an 825CFM (actual flow is 975cfm ) Drag Race Demon ( double pumper w/ mechanical secondaries ) tuned with my LM-1 wideband A/F meter to get optimal performance.

I have a 3.08 rear end with a Tremec 5sp transmission and on the highway in 5th gear my RPM's are about 1700 @ 70mph. Around town if I don't get on the happy pedal I get the mileage above, but I am always on it so the MPG would be less than 15

7T1vette

For highway driving (70mph or less) and with 3.36 or less rear axle ratio, you should get around 15-17 mpg, if properly tuned. If your rear gear is steeper, that will go down.

The same vehicle with an overdrive transmission (manual or auto) will get 18-21 mpg.

In-town mileage is substantially lower, depending on how much idle time the car sees. 10-12 mpg is normal.

mrvette

I very surprised at what you say, as I did manage to get 14 out of the old Qjet around town, but when injection was installed it went to 18 around town....and like a said 24 at 80 turning 4k rpm.....which shocked me so much, I did the calculations over several fill-ups..... wish I got 24 on my 2 mile round trips... I could run a 6 mo to a YEAR on a tank of gas.......

rcread

I'm still on my first tank after building a new 350. I'm looking forward to finding out. My old L48 got about 12 mpg. The new engine makes a ton more power.

upnorth

last time I checked 8 with my holley 600 .been setting up a new quick tune hr 680 have gone through a 1/2 tank of gas and have 21 miles on it wont count this one .

74 LS4-454

With my 82 on the commute back & forth to work, get anywhere between 18.5 to 21.4 mpg depending on my right foot....
On long extended trips have seen high as 24 mpg, but that is few and far between to say the least.
Well you know the CFI combo....the OD helps out very nicely.

On my 94 ZR-1, I don't really check the mileage I just add gas and go.....

And I'm hoping that my 74 BB Vert whenever it's completed with get decent gas mileage. It has 3:08 gears and the TH400, which I will probably keep. Was thinking about a 200R4, but won't probably be necessary even with the few times I would take the 74 on a long trip.

The 82 is the only one I am concerned about with mpg, since it is my "dd".

Priya

79 L82 4 speed, 3.70 gears - 15 miles to the Canadian gallon on the highway at 100 kph.

REELAV8R

That's about what my stock configured "77 got too. Best was 14 MPG on the highway @ 70 MPH. Timing changes and carb rebuild via cliff ruggles' book, electric fan conversion got it up to 20 MPG combined and as good as 24 on the highway.
Now with rebuilt and 380ish HP I get 19 MPG combined, don't know the highway mileage.

'75

L48, vortec heads, quadrajet, 2004R, 3.55 gear, 20 mpg running 80 mph on the freeway,

mysixtynine

69 convertible

Iron head 509 big block 850 holley tko 600 3.55 rear.

Just got this thing mobile again after 7 yrs body off.

Tires are over 20 years old or more so I won't take it on highway yet until replaced. All city driving 1st tank of gas got me 8.7mpg.

Decided to align all 4 wheels when I saw rubber dust both front and back fenders.... Was just driving on basic setup since rebuilding everything.... It was a mess. Front was 7/16" toe out and rear was 1/2" toe in. Front tires inner were starting to cup and rear tires outer were cupping already .(again old beater tires)...Took me all day to set up alignment .... Too much up down and rolling back and fourth...engine actually sounds less strained riding around now. I was getting wheel hop getting on it... So now I am hoping for smooth burn outs.

Hoping for 10 mpg city with clean alignment.

doorgunner

I won't know until I "unweld" those 4 jackstands from under the frame

My '06 Escalade gets 22mpg interstate driving/70 mph/2200 rpm.................

I wonder what mpg the 6.0L would get if it somehow "jumped" into my project car......there would be a 2,500 lb. weight reduction!

JimLentz

Yes, I have 2" dual exhaust with no cats.

jb78L-82

Used to get around 14 MPG with the OEM L-82 4 speed 3.70 gears. The rebuilt L-82 with AFR heads, roller cam, 10.2:1 compression and a ton more power definitely does better but i have not measured it...spend too much time with my foot heavy on the gas..

pltmgr

Don't know what mileage I get on any of my collectibles. Not too concerned because gas in the cheapest thing I buy for them