I just check on my 409 with 4 speed stick the mpg and I come up with 8 mpg the motor is stock it has a 750 holly demon i would think it would get a little better than that.
with a car like this i am not worried about the mpg , I would like to see what other are getting
I got about 11-12 MPGs while free way cruising in a 1962 ImpalaSS with a stroked 409 running dual quad AFBs. Rear end was a 3.36 posi, transmission was a Borg Warner T-10.
I have no idea what she got on the streets, never checked .
My 32, 409 (414 now) TKO 600 will get 15-17 on the highway. GM OEM 425hp carb and intake setup progressive linkage, Joe Hunt Magneto 11-1 comp, and an Aubrey Bruneau solid flat tappet cam shaft, 246/256* dur @ .05.
Likes to cruise around 70-75
The first road trip on my 65 low horsepower 409 with 2.73 and Muncie m 21 I got 15.7 kept it 70 mph and under; surprised the hell out of me; thought if I got 12 mpg I would be lucky.
I have had several people ask me about gas mileage in the last few years and I usually replied that my two four's if I drove the car probably wouldn't get 10 MPG if falling off a cliff.
Robert
What is your rear axle ratio and do you have vacuum advance on your distributor?If you have lower than a 3.50 gear ratio and lack any vacuum advance on your distributor,every time you let off the gas it will feel like your stepping on the brake pedal due to engine braking,and the higher the compression ratio or the lighter the car the more noticeable it will be.The vacuum advance mechanism is critical to getting good mpg on a street driven car,part throttle cruise and coast is where you will get your mileage and that's when vacuum advance comes in.
As i recall the 750 is mechanical secondaries and 780 is vacuum. If my memory is correct swap carb and tune those secondaries. Ive had several vehicles ive swapped those carbs and got real good results. You could always consider swapping that 4 for a 5 speed or changing rear gears.
The only thing you need is over drive. I'm running a power glide right now and I know it gives me horrible fuel economy. The 700r4 on the ground next to the car will fix that but I probably won't get better than 17mpg on the interestate if I'm lucky. My truck weighs more and is a 3/4 4x4 and it gets almost 16 with a 700r4 down the highway. For your manual set up a 5 speed would help a bunch.
All of my early Ford hot rod buddies, most with belly buttons under the bonnet, that have a 4 speed or 1-1 top gear are happy with 10. As discussed OD lockup automatic of 5 speed will fix it.
With a car as light as an early Ford, you can lean your cruise mixture settings some and make a noticeable difference.
I had a new 63 Impala SS, 425 hp with 3:70 posi rear, that was a long time ago but if I remember correctly it usually got about 11 to 12 mpg. I remember driving it from Richmond Va to the races in Daytona in the winter of 1964 , had 3 guys riding with me and the deal was I provided the car and they split the gas. They were crying by the time we got home.