1957 8 MPG

I've tracked the MPG on my 57 (automatic with P/S and P/B) since I bought it 6 years ago. It started out at about 10-12 MPG, but after some work (that I didn't do), it's averaged about 14 MPG over the entire 6 years. Added A/C in 2019, but haven't driven it a lot with the A/C on, so can't judge the effect it might have had on the MPG.

BTW, I started using ethanol-free fuel (when possible) about a couple years ago or so. Doubt that this had impacted the MPG, but hopefully will make the fuel system last longer without having alcohol-induced problems.
 
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I have been using 90 octane, 100% gasoline for over 8 years now. I don't think it has increased my fuel mileage any (13.24 MPG), but I no longer have any hard starting or vapor lock issues. I am fortunate that there are 2 gas stations that sell ethanol free fuel within 5 miles of my house.

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doug7740
1955 Thunderbird Blue
 
Well, Just checked again. 8.8 MPG. Does not smell rich in the exhaust, Runs great But it was a rebuild from the mid 70's. Don't know the specs of the engine or how much over bore was done. Blew a head gasket at 500 miles as I forgot to re-torque the heads after break in and had them planned to make sure.
My engine may be more potent than stock and hence the poor MPG but I'm not complaining.
 
Are you sure your timing is correct and your mechanical advance is correct. It sounds like your engine is retarded. FYI, I found I could advance my distributor from 6 degrees to 16 or 18 degrees without pinging and that helped response and gas mileage.
 
Bruce Hardy said:
Are you sure your timing is correct and your mechanical advance is correct. It sounds like your engine is retarded. FYI, I found I could advance my distributor from 6 degrees to 16 or 18 degrees without pinging and that helped response and gas mileage.
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It's been tuned to spec.
 
Most purist would never change the original carb - but I'm a driver so I don't care.
I've had 4160's & Edelbrock's of various years ...they're all problematic.

I changed my carb over to the Street Demon 625 CFM and it's the BEST carb I've ever installed.
The primaries are half the size are the originals and the secondaries are huge.
I will test but I definitely saw an increase (easily 3 MPG) in a 100 mile jaunt on the way back from a show......the drive down was all about opening it up and getting the "whomp" of the secondaries.

I'' shoot a video of the secondaries opening and the sound, my rebuilder / restorer who worked on the suspension said it's the best carb he knows of.

If you're all about driving.......upgrade you will be impressed.

I forgot to add ...my bird is a 390 FE with a recent valve job and slightly taller tires .....at 55 mph my vacuum is low and the secondaries don't sound like they are open...when I get on it and drop a gear the womp is nothing like the original....it's the best. If you remember the early QJet Sound you'll know what I mean.
 
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Ward 57 said:
It's been tuned to spec.
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It has always gotten this milage. Stock carb, runs great and torque that is astounding. A touch of the throttle and doing 35MPH in a heartbeat. Horsepower is handy if you want to spin the tires but torque is what gets a heavy machine moving with grace. All the older cars had torque numbers above HP.
When I stomp on it and the secondaries open, it howls through the hood scoop and rumbles out the back pressing me back in the seat. I have no complaints just wondering what others see.
 
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Ward 57 said:
Well, Just checked again. 8.8 MPG. Does not smell rich in the exhaust, Runs great But it was a rebuild from the mid 70's. Don't know the specs of the engine or how much over bore was done. Blew a head gasket at 500 miles as I forgot to re-torque the heads after break in and had them planned to make sure.
My engine may be more potent than stock and hence the poor MPG but I'm not complaining.
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Ward,

Since you are commenting on the post you started in July 2022, tells me that there is something wrong with your car and you would like some more suggestions on how you can increase your fuel mileage. As it states in the article below, normal fuel mileage on a 1957 Thunderbird with a D 312 engine is between 12 to 14 miles per gallon. If you are sure that the carburetor is functioning properly, the ignition timing is set correctly and that the distributor vacuum and mechanical advance is in good working order, then a slipping converter sprag could be the cause of your low fuel mileage. That is assuming your Thunderbird has an automatic transmission.

doug7740
1955 Thunderbird Blue

Fuel Mileage.jpg
 
Ward 57 said:
It's been tuned to spec.
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Then maybe check your float levels. Obviously something is not right. As an example,I've got a 5.0 in my 55. dual quad dyno'd at 410 hp. 5 speed 3:23 rear I get 17.5mpg consistently.I have 2 390 CFM holleys that I tuned myself.I run 16 degrees initial advance with a total of 32 degrees . Some how you've got to find the problem because I think your washing your cylinder walls and gas is getting into your oil pan.
 
Hey @Ward 57 , maybe it's time for you to check the jet sizes in the carburetor. An over jetted carburetor will give very poor mileage and can still be tuned to idle correctly.
 
Bruce Hardy said:
Then maybe check your float levels. Obviously something is not right. As an example,I've got a 5.0 in my 55. dual quad dyno'd at 410 hp. 5 speed 3:23 rear I get 17.5mpg consistently.I have 2 390 CFM holleys that I tuned myself.I run 16 degrees initial advance with a total of 32 degrees . Some how you've got to find the problem because I think your washing your cylinder walls and gas is getting into your oil pan.
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No soot, recently rebuilt carb I bought from Ford 40yrs ago as a specific fit, exhaust does not smell rich, oil smells clean has more than enough power. I can watch the advance with my timing light and all seems normal.
When I replaced the plugs they were of uniform and proper color. It's just thirsty and I don't really have an issue. This engine has always been this way since it was installed 40+ yrs ago. I wish I knew the specifics of it's build but I was young and naive at the time so never asked.
 
Ward,

Since you feel that everything seems normal, then a slipping converter sprag could be the cause of your low fuel mileage. That is assuming your Thunderbird has an automatic transmission. Only getting 8.8 miles per gallon is not normal.

doug7740
1955 Thunderbird Blue
 
doug7740 said:
Ward,

Since you feel that everything seems normal, then a slipping converter sprag could be the cause of your low fuel mileage. That is assuming your Thunderbird has an automatic transmission. Only getting 8.8 miles per gallon is not normal.

doug7740
1955 Thunderbird Blue
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I have no idea what a converter sprag is. I feel no slippage, delay or any kind of operational deficiency. I did have the transmission rebuilt many years ago after the engine install. I'm not planning on any major repairs or investigations and the car is running better than in years.
It's a pleasure machine and the price of fuel while running mean, clean and smooth is a small price to pay.
 
The converter sprag is a one way clutch inside the torque converter that allows the stator to turn in one direction but not the other. If the converter sprag was starting to slip you would not have any transmission slippage, but some of the torque multiplication could be affected lowering the fuel mileage.

doug7740
1955 Thunderbird Blue
 
doug7740 said:
The converter sprag is a one way clutch inside the torque converter that allows the stator to turn in one direction but not the other. If the converter sprag was starting to slip you would not have any transmission slippage, but some of the torque multiplication could be affected lowering the fuel mileage.

doug7740
1955 Thunderbird Blue
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Thanks for the info. Unless it wasn't properly rebuilt it has always been this way. Plenty of torque from what I can tell but I have no reference point.
 
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