Hot Rods Flathead Gas Mileage

I was kidding an AACA buddy of mine last week about the gas mileage his 56 Caddy Convertible with 2 - 4 barrels must get. He laughed and said,"Man, I get 10.5 mpg with this car. My 40 Ford only got 8! I've gone Green!" Lol!

I was shocked. He said at every AACA event he had participated in, 40 Fords got between 7.5 and 8.5 mpg. is that true? Does mileage get better or worse with modifications? I suspect the lack of a vacuum advance plus low compression are the main contributing factors. Inquiring minds want to know.

 

FWIW on both of my flatheads, one 8RT and the other a 8CM (Mercury version with slightly larger displacement) I get around 15mpg in summer highway driving. I can get a little better on longer sustained runs on the highway. Fall, winter and spring quite lower as the trips are typically shorter and the warm ups longer. Caveats: one car has overdrive and the other a 3:55 rear.

 

I get a little over 20 mpg on the highway in my 39 with OD trans.

 

I'm getting smiles per gallon !

 

Gas mileage is just a number. I guess smiles per gallon would be a number as well, but a more worthwhile number to keep track of.

 

Poor range or fuel economy just means your shit ain't tuned right. One thing I noticed, crankcase oil stays nice and clean a lot longer with a good sharp tune, and the plugs don't foul.

 

Every thing done to my 265ci 8BA including .425 lift cam. around town, 8-10 mpg with two 2Brls,
16-18 with M90 supercharger and Q-jet & Lots more FUN!!!

 

My 40 has a stock 59AB with a single stromberg. It´s finally getting 15-17 mpg since I replaced all the brittle and leaky rubber fuel lines. To my experience excessive fuel milage often has a lot to do how leaky your fuel system and how well your tuning is. I brought my 65 Riviera from 8 mpg to 13 just by replacing the gas tank cap with a new one. Another 2 mpg came with replacing the leaky hoses and rebuilding the AFB , converting to Pertronix did not improve anything .
I also helped my buddy to improve the mpg on his 62 Impala. The connector hose between the filler tube and the tank had dry rotted, and it was fine while he filled up. But on right turns the fuel would slush to the left and drain from under the car... He had been complaining about bad milage for years, took a while until we found the issue.

 

When I had my 53 Ranch wagon as my daily. It had a stock flathead except for headers and duals.
The biggest gain came from a 6 volt alternator for more juice.
It had overdrive and on a my daily 82 mile one way commute it got 21 and in town it got 15-16 mpg.
If your flattie is getting 8 then you need to open the hood and get to work. Retarded timing is a gas mileage killer.

 

From various sources, Fords from Model T to Model A, to flathead V8 to Y block got around 17 MPG. Over the years they got more efficient but that translated into more power and speed, not better mileage.
The OHV six in the 52s was good for 20 or so, and in the sixties they went after mileage with the Falcon 6 and small V8 Fairlane, those were good for 20 (V8) and up to 25 (Falcon 6).

 

Maybe he was talking "around town" driving. You've convinced me it could have been a lot better, which is what I thought.

 

Usually in the mid teens for mpg. Remember; flatheads sound like no other, like gasoline, use oil & mark their territory.
Ain't that why we love them ?!

 

Don't know what mine got but gas was around $.18 a gallon so I didn't care. 1962 with a 50 Ford.

 

And you made how much an hour? lol....

 

Modifications done right will improve the efficiency of any motor. That is the whole point of modifying. Case in point, I own an SBC (a 355 that we call it the Timex motor) that makes a little more then 400 horse with torque numbers in the 440 pound foot range. It has consistently got mileage in the 20 MPG range since we first screwed it together in 1997 and has done that in any of the 5 or so bodies it has been in.

There are s few hurdles to overcome when trying to upgrade a flathead. one is that they are a low compression motor, to get efficient fuel burn one of the things that are required is compression, I like to see it in the 10-11:1 range for a street motor but even increasing to 9-9.5:1 will show a marked improvement in fuel burn.

next you must consider how your gas/air mix is delivered to the motor in question. Most flathead intakes are not very efficient and to make one efficient is to loose that traditional look. Then you have the problem of breathing, flatheads by nature do not breath well. Traditionally many things have been done to try and jump that hurdle including making one breath backward, IE intake through the exhaust ports of which there are only 3. There are things that can be done obviously to optimize breathing but you are still working with a poor design in that dept. it works it just does not work well.

Now all that said we did get 14-16 MPG out of our merc flathead when I was in high school. It was not stock but not highly modified, and was backed up by a 3 speed OD.

 

I have a '51 Mercury in my '51 club coupe. he engine is slightly modified with an updated ignition, Edmunds heads massaged for optimum quench and compression, and a Rochester 2G carburetor. I have no OD at present (one is going in this summer), 3.55 gears and 225/75 15 rear tires. I get 15 mpg in normal use and two years ago took a 300 mile highway round trip on which I got 19 mpg running an 65-70 most of the time.

 

I drove several different flathead cars during the late fifties & early sixties.
Very few road trips, mostly just daily driving. Ten to thirteen miles per gallon is what I remember.

 

Hmmmm, there may be something to this raising combustion efficiency, more modern carburetion, and better ignition thing after all.

 

Even with 2 97's I don't care. When the gauge gets to 1/4 I put more in.
Having too much fun. Now the 05 Chrysler 300C Hemi gets around 12 around town, better on a trip.
Paul in CT

 

The second owners of my '40 used it for several cross country trips in the early 50's and kept logs of the fuel usage that came with the car when I got it. Stock 221 with 3.78 gears and 6.00 - 16 tires averaged 18.5-19 mpg at the highway speeds of those days. Of course these days, with a Cad 390 w/dual quads installed it doesn't quite achieve those numbers...

 

Low compression engines especially ones which dont breathe well do well at low RPM. Overdrive and tall gears help.

 

I remember reading that in the early 50s the winner of the Mobile economy run was usually a V8 Mercury, getting 26+ MPG.
No doubt they were trying everything they could thin of to do that, but it proves it could be done.

 

View attachment 5070849 View attachment 5070849 I'm with 4ty. Gets to 1/4 tank I refill , and still runners " smiles per gallon " Drove mine last Sept from Md to Springfield Mo. Almost 2200 miles round trip. Charged all the fill ups to check mileage and keep track of what I spent . Had lots of "smiles per gallon" never took the time to check milage how many times I stopped , amount of gas used and different prices along the way. Maybe this year I'll keep better records ,expecting my wife to go if we make the trip . Southwest 40 ford 80 yr reunion .2020 . 8ba 3 two's electronic ignition , 355 gears . Run 60-70mph most of the trip . Changed to these bigger air cleaner filters after trip .

 

I've had several people ask me about the mileage on my V8 A and don't have a clue, warmed over flat, dual 94's, closed Ford trans and rear end with 3:54 gears. I'm guessing probably 12-14 mpg but didn't build it for mileage and having fun with it.

 

Guess I don't understand.

I mean, put it this way. What is there to smile about if say, you could get 20 mpg but you're only getting 10?

There's no performance benefit to literally spewing fuel out the tailpipe (performance may well be worse) and a mistuned engine tends to foul spark plugs, dilute crankcase oil, increased cylinder wear, among other things. I mean sure, it's only money, but that doesn't make any sense. Performance and mileage go hand in hand, believe it or not.

For my part I actually like road trips in out out the way places, everything from 4WD trails, gravel, remote highways and byways, backcountry national forests, deserts etc. Best range on a given tank of juice, is way mo' better.

 

My Uncle told me the best way to get better fuel economy than your buddy,..............have him tell you what he gets first.

 

Mine gets just under 10 MPG so far but I flog it... a lot. Progressive linkage keeps the end carbs out of the equation until half throttle. 4:10's in the QC, 5 gear. No, that is not my carb adjustment tool on the lift arm. That was for making a fine tune adjustment to my "hencho in Mexico" SW wings oil pressure gauge.

 

16mpg with by 8BA F1 on a good day.

But then again we use Imperial Gallons (Until litres took over)

 

My 8ba in the 37 coupe gets 14-15 around town and 18 highway. Two 94’s.
My 34 pickup has had three different 59 engines at various mild and hot rebuilds. All running the same intake, carbs and ignition.
All three engines ran at 10mpg regardless.