340 stock gasmilage

[Qda71]

1971 340 Stock rebuild
J heads
Stock manifolds
It has:
Edelbrock avs1 650
Pertronix ignition
Sg 3:23
727 auto

Freeway driving 60 mph

12.3 mpg!!!

Spark plugs tan and clean no black smoke or gas smell

Alignment done
new radial tyres
no draggin

[Katfish]

Sounds about right, 340/518/3.73/60mph = 16.5
That's with OD, so it matches yours.

Same exact car, swapped in 5.7 for the 340, 150 more HP and now gets 20mpg.

[jimynick]

LOL! My '67 Valiant, 340, 4 speed, 3:91SG could often see less than 10 mpg- and that's an Imperial gallon of 160 ozs not the American 132. It depended how much you liked to hear the engine rev, who/what was beside you and how heavy your right foot felt. In my opinion, if you're getting 12+ you're probaly pretty average. Some will get more and some will get less. Price of admission and the reason the overdrive guys are in business. 

[71vert340]

The best I've gotten with my stock 71 Challenger 340-4 speed and 3.23 sure grip has been 22 mpg at 55-60mph on highway. It has the stock TQ carb and stock dual points ignition. Never kicked in the 4bbl on that tank. Averages at 65 to 70mph about 19 to 20mpg on highway if I don't kick in the 4bbl. Standard 14 inch rallye wheels.
 Terry W.

[chargerdon]

1971 340 Stock rebuild
J heads
Stock manifolds
It has:
Edelbrock avs1 650
Pertronix ignition
Sg 3:23
727 auto

Freeway driving 60 mph

12.3 mpg!!!

Spark plugs tan and clean no black smoke or gas smell

Alignment done
new radial tyres
no draggin

What size wheels and tires do you have?  What rpms at steady 60?   I have a 74 360/408 with 600 cfm Edlebrock, and a hot lunati voodoo cam.   With th3 14" wheels and around local driving i get about 10 mpg.  But out on a highway doing 70 with the A518 overdrive engaged and lockup torque converter i got 17.5 on one 50 mile round trip to a car cruise.   Its the RPMS   

[Qda71]

15" 255/60
I dont have ralley dash / no tach

[chargerdon]

Easy enough to hook up an aftermarket tachometer.  It will tell you a lot.   With 15" wheels and a 3.23 axle you are probably turning around 2500 RPMS at 60 and near 3000 at 70.   An overdrive would definitely help on freeway type driving.