Hi guys,

After a 2 years full restoration of a 66 Mustang convertible I'm a little worried about my gasmilage. I have a standard rebuild 289 with an autolite 2100, c4 automatic and 3.00 open diff. I only get 12 mpg with this combination which is a bit high to my opinion. I drive 50% city and 50% highway at 60-70 mph.
I've rebuild the carburator and replaced the 58 size jets for 50. The carburator has the 1.14 stamping, C5ZF-B part number and everything looks normal and works fine. Choke symstem works fine and doesn't stick, no black smoke and good accelaration. So is this 12 mpg OK for this combination or can it be much better? If it can be better what could be the cause for this milage?

Thanks,

Erwin, The Netherlands

Heres the bottom line the present day 289 the 5.0 (302 fords can easily get 25 miles to the gallon. But milage is so inter-related with everything else, condition of engine,condition of engine components, weather, how one drives, even the fuel itself that to make blanket reccommondations is really a shoot in the dark.
My best recomendation is to get a vacuum gauge from JC whitney and install it and visually see where you are wasting gas, trust me anyone who has ever observed a vacuum gauge realizes how they can save fuel.
Otherwise make sure you carb is properly set to factory specs, ignition is top notch, tires set to specs (want a old time gas saver tip, overinflate your tires by 5 lbs, in the old days every service station that did tune-ups did this to all their tune-ups since 90% of people have at least one tire that is below proper inflation levels it looked like the tune up yielded instant results.) good adjusted belts and even proper operating thermostat can effect fuel milage.
carrying extra things in your car,maybe an emergency kit? or tire chains? 100 extra lbs will decrease milage.
I would think that 12 is on the LOW side for milage for a 289 2 barrel. I would think about 15-18 would be better and excellent milage for your mustang.

Good Luck,

Bill White
White Automotive

Thanks for the answer Bill. I just ordered a vacuum gauge. I get back to you with the results.

Thanks,

Erwin

Ours is a 64-1/2, stock 289, 4100 1.12 Autolite, c-4, 3.00 gear. On the highway at 60mph, trips of 50 miles or more it will get 20-21mpg. In the city, it can get as low as 12mpg (trips of a couple miles in cold weather, maybe 16mpg tops. So it really depends on the driving.

But on a long trip at 60mph yes you should be close to 20mpg if its tuned right. At 70mph it would drop to maybe 18mpg highway.

Make sure it is jetted until the exhaust pipes look right (not black but light gray after a long trip) and the plugs stay clean. And, total advance (initial plus mechanical plus vacuum) should be 40 to 50 degrees at cruise rpm, any more or less than that and it will not be happy.