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By 55blacktie - 4 Years Ago
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There is a recent post on one of the Thunderbird forums, regarding the gas mileage of 55-57 Thunderbirds with 292-312 Y-block engines. Some owners reported 7-10 mpg, others getting 9-12, another getting between 13-14, and another claimed 20 mpg on the highway, in overdrive. Having inherited my 55 T-bird, I drove it just a couple of times before beginning restoration, so I have no idea what kind of gas mileage I should expect. 7-13 mpg is nothing to brag about. Are these numbers typical? They are awfully low for a small v8 in a 3,000-lb. car. Is there an explanation, other than the given examples are parade cars that are seldom driven on the highway?
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By Tedster - 4 Years Ago
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There are lies, damned lies, and fuel mileage claims, er Statistics.
Most any OHV V8 in good tune and suitable gearing in a car though is fully capable of 20 to 25 hwy mpg with careful tuning. There is no need to give up performance either. Most people aren't that interested in the finer points of Tune-Ups.
Keep in mind a well tuned motor will not pass any sort of pollution testing for NOX emissions when running optimally for power and economy. This was one of the insults added to the injury of the oil embargoes, dollar devaluations, and the 1970s federal pollution mandates, the engines Detroit was putting out were notably unreliable low powered absolute gasoline hogs. They broke many engine tuning "rules" to achieve the pollution requirements. There was a whole cottage industry of mechanics restoring engines to their pre-smog configuration.
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By DANIEL TINDER - 4 Years Ago
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When I first got my ‘55, mileage was over 20mpg on the highway (in overdrive). But, after installing a Pony teapot and then rigging my Loadomatic distributor with an aggressive curve (including an advance limiter, which unfortunately did away with the factory ‘crushing vacuum’ economy feature), mileage went to hell (don’t even bother to measure it anymore). But then, I also compound the misery by buying 93 octane (which is likely overkill), and justify it all as a ‘recreational expense’.
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By Tedster - 4 Years Ago
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What has really surprised me, with any carbureted engine if it isn't tuned properly a truly astonishing amount of fuel can be simply wasted, spewed out the tailpipe, with no discernable smoke (nor any performance benefit).
A mistuned engine will tend to foul spark plugs, when extreme. With modern unleaded oxygenated gasoline formulations especially, if the spark plugs are fouling at all, the fuel curve is extremely rich and crankcase oil dilution and even washing out piston rings is a possibility. The Load-O-Matic was designed with economy in mind wasn't it? But I'm not sure if worked very well in the real world.
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By 55blacktie - 4 Years Ago
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I don't think my dad drove my 55 far enough/often enough to calculate an accurate mpg. It was almost 100% original, but I discovered that it had a 57 distributor, even though it still retained the 55 Teapot. Upon learning that the 57 distributor is not compatible with the Teapot, I began the restoration. Before my dad passed, I installed a Casco wp and converted to 12v. It had the Fordomatic/w 3.31 gears, no power steering or power brakes. It will not be stock when I'm finished, but retaining all take-off parts.Even with my engine mods, I expect a light foot, combined with 2.72 gears, will see better highway mpg.
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By charliemccraney - 4 Years Ago
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For what it's worth, mine averaged a little over 16 on the highway the last time I checked. In the mountains, it was around 12 and on flatter hwy, around 20. I think it can do better than that because the gearing is not right. It's mostly in the range of 1800rpm to 2000rpm while keeping up with traffic and while the engine seems to do fine, it sounds happier above 2000rpm and the way it's built, probably should be above 2000rpm. I've never checked city mileage but for the typical mileage I put on it in a week (Atlanta Suburbs) and the amount of gas it takes to top off, that is around 15mpg, which is about the same as my '88 Firebird, which is fuel injected, roller cammed and should be a little over half the power (stock), for perspective. The Firebird does get about 28 on the hwy, though.
A T-Bird should be more aerodynamic than my truck, so I think 20s on the highway and teens or better city is possible in good all around tune and setup. Note that this probably doesn't mean stock.
If at all possible, install an oxygen sensor and tune the carburetor with that. If you want the interior to look stock,. figure out a temporary means of installing the gauge and remove it when tuning is done. This takes a lot of the guess work out and provides a lot more info at one time than reading plugs because you can see what's going on at idle, at cruise, under load going up a hill, during acceleration, etc, all in one drive and don't have to deal with pulling hot plugs on the side of a busy road to see how it is doing. Some of the fancier 02 setups can data log so you can record the data on your laptop and take a look at it later.
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By Tedster - 4 Years Ago
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55blacktie (6/1/2021)
Upon learning that the 57 distributor is not compatible with the Teapot, I began the restoration.
It would be more correct to say that the LoadOmatic distributor is only usable with the factory Teapot carburetor, as these were designed around two different sources or types of engine vacuum. As you know there is no mechanical or centrifugal advance in these distributors.
On the other hand, a post '56 dual type distributor can be made to work quite well with any common source of engine manifold vacuum. Some people actually prefer this. The LoadOmatic distributor needs the Teapot, but, the reverse is not also true.
As I understand it, interestingly enough T-Birds have somewhat of a reputation for running hot or overheating, and any engine with a manifold vacuum distributor connection and a conventional dual distributor will generally run noticeably cooler at idle, cruise, and stop and go driving. This would probably be worth investigating if other remedies weren't panning out in this situation.
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By 55blacktie - 4 Years Ago
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I'll have an O2 bung installed in the Sanderson reducer during rebuild. RPM @ 65 should be about 2200. Cam range is 1800-5000. C4 transmission.
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By Joe 5bird7 - 4 Years Ago
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Several years ago I drove my '57 (312 and overdrive) between LA and the Bay area quite often (400+ miles) and routinely got 21/22 mpg.
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By DryLakesRacer - 4 Years Ago
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55Blacktie. A Thunderbird might be different than the full size car but during my transmission and rear end swap I was advised not to use the Ford-o-matic with the new rear I was installing with 2.74 gears so I did the true 3 speed automatic first. I agree that at highway speeds the new rear is great and is not sluggish at all starting out because it’s using 1st gear. Automatics use a lot more fuel at idle which doesn’t help our mileage.
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By ian57tbird - 4 Years Ago
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At one time I was regularly checking mileage on mine. 3.1 rear, G78x14 tyres, auto, stock 312, I would always get a combined of around 16-17Imp mpg = about 13.5-14US mpg.
Could possibly do better, as I'm will put my foot into it on occasions, and I don't drive slowly.
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By 55blacktie - 4 Years Ago
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Drylakesracer, there's a lesson to be learned, here: Keep moving! You'll get better mpg, and your car won't overheat. It might be easier, if I move from California.
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By paul2748 - 4 Years Ago
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The last trip I made coast to coast in my 56 Bird, I got an average of 14 MPG. This was all kinds of driving - flat plains, high mountains, city and country. 6300 miles total. 312 with a C-4, stock rear
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By MoonShadow - 4 Years Ago
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When my van broke down I drove my 56 Vicky, 325 cubic inch, 4-71 blown y-block from Cincinnati to New Hampshire. I do have an AOD overdrive transmission and I think around a 3:80 rear gear. I averaged a high 17mpg with steady highway driving around 70. I was a bit shocked by it.
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By 55blacktie - 4 Years Ago
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Thanks to all. I will recommend that the members of the T-bird forum read these posts.
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By PF Arcand - 4 Years Ago
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The issues with the "Loadomatic", pre 1957 distributors, which don't have centrifical advance has plagued Y-block engine owners for years.. Because, if using a 1957 & later Carb with that vacuum only distributor, the setup will not work properly. Nor will an original stock Holley 4000 'teapot" work properly as is, with the 1957 & later Distributors. For proper info on that later issue," Link" from this site to "Ted Eaton's Balancing" site & scroll down to his instructive article on modifying the Holley Teapot carb to work with the 1957 & up distributor..
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By Tedster - 4 Years Ago
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PF Arcand (6/2/2021)
Nor will an original stock Holley 4000 'teapot" work properly as is, with the 1957 & later Distributors. & up distributor..
The "Teapot" carburetor doesn't care what distributor is used, although it is true there is no source of ported vacuum below the throttle plates. That's what the carburetor modification is about.
But manifold vacuum (from whatever source derived) can be made to work perfectly well with a dual distributor, I wouldn't let the carburetor be a show stopper when considering whether to ditch the LoadOmatic. Achieving a perfectly steady idle RPM can sometimes be an issue (which incidentally was why the "ported" type of vacuum signal was invented).
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By Ted - 4 Years Ago
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My two cents worth.
Like most engines, the Y likes an overdrive transmission. Allowing the engine to run steady state at 3000 rpm versus 2200 rpm puts any engine at a definite disadvantage for any bragging rights fuel mileage numbers. The lack of overdrive puts the early Ford-O-Matic trannies equipped vehicles at a disadvantage when comparing the fuel mileage to a car or Thunderbird equipped with overdrive. To compound the fuel mileage issue with the older engines is the addition of ethanol into the gasoline which forces the need to increase the volume of fuel going into an engine to maintain the ideal fuel/air ratio. Going too lean on fuel mixtures can have the engines actually using more fuel as they then have to be driven deeper into the throttle just to maintain a given speed. The Holley Teapot carbs are sensitive to the addition of ethanol to the gasoline and many require an increase in the primary jet size to compensate for a lean condition that creates a hesitation issue. Another issue that crops up for the fuel mileage is the second ring wear. The second ring in many instances is a tapered ring and as it wears, the ring drag against the cylinder wall is increased. Up to 40K miles, that piston drag is much lower than what you will find with the same rings reaching the 100K mile and more mark. As the friction within the engine increases, the necessary fuel required to overcome this must also increase. Reduce the friction and you will reduce the fuel requirements.
My ’55 has almost 200K miles now since having new pistons and piston rings installed in 1989 and the fuel mileage now with what I’ll call local driving is now averaging 15-16 mpg. Back in its heyday, I did see 21 mpg on occasion when highway driving but 19mpg was more the norm for any trip mileage. That car has a BW 30% overdrive tranny with 3.56 rear gears while the 272 engine does have an Isky E4 camshaft and now with a Summit 500 cfm 4V carb. Looking back at my fuel mileage records, that car still averaged 13.6-15.7 mpg during the weekend I raced the car at the Big Bend Open Road Race. At that time, the car had a Speed Demon Jr. 525 cfm carb. That race is 118 miles long and the car was entered in the 90 mph class with speeds up to 110 mph being recorded when needing to make up time for curves, hills, and other impediments to maintaining a 90 mph average. And then there was also parade duty which also didn’t help the fuel mileage.
It should go without saying that the condition of the engine and its tune up is paramount in getting ‘good’ fuel mileage. Keep those comments coming.
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By tbirddragracer - 4 Years Ago
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I have a "57 T-Bird " C " car with a 292 engine, 2 bbl. carb with a 3 speed standard transmission. I swapped in a 3 speed
overdrive transmission with a 3.10 rear gears. I did not make this swap for the mileage, but to reduce engine rpm's, so I
rarely checked mileage. On one trip from Tyler to Denver Colorado, a couple of mileage checks showed slightly
above 24 mpg. This was without driving for maximum mileage. A well tuned engine is essential for best results.
Ernie
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By 55blacktie - 4 Years Ago
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My speedometer was about 15% fast, which seems to be common, original transmission and 3.31 gears, and 205/75R15 tires. On one hand, my car has fewer miles than indicated by odometer. On the other hand, gas mileage is worse than indicated. Hopefully, C4 transmission, 2.72 gears, and metric rings will show an improvement. Once the rebuilt engine is broken in, I might consider swapping carb for FiTech. The car will never be a daily driver, but might as well make it more efficient during restoration.
By the way, my 2015 Toyota Rav4 and 2017 Ram 1500 miss the mpg mark. There is a big difference in mpg between driving 65 on a flat highway/w little traffic, and driving around town, no matter what you drive. For what it's worth, I had a 1988 Mustang 5.0 convertible/w AOD and 2.73 gears. It was capable of over 25 mpg on the highway, and 18 mpg in town. I think Ford got it right with that one.
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By MoonShadow - 4 Years Ago
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I have a Dodge 3500 maxi van. One of several I have owned over the years. The 360 engine with an overdrive automatic will get 14+ around town and about the same on the highway. As soon as I hook up my car trailer I'm lucky to see 7mpg or less depending on driving style. The only way I've found to improve this is to backward convert the engine to a non-electronic set up. Parts cost is in the thousands. 
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By Town Vicky - 4 Years Ago
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Let us not forget gas was 20 cents a gallon back than and most people wanted power
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By Dobie - 4 Years Ago
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And the average working man wage was prolly around 10 to 15 grand/yr...
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By 55blacktie - 4 Years Ago
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More like 5-7 grand. 10-15 would have been extraordinary. I'm 66, and I can't remember gas being less than 26-cent/gal. Maybe in the 50s? I remember my dad's take-home being $86/wk. in the early 60s.
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By KULTULZ - 4 Years Ago
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Let us not forget gas was 20 cents a gallon back then
And you got free dishes ... 
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By famdoc3 - 4 Years Ago
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My 57bird has an .80 over 312 with the Isky 300 series cam and an E manifold with dual throttle body injection and 2.73 rear. Highway mileage is 18/gallon, town is 13 or so. Has a super T10 with a 2.64 first gear to launch a little better. Has way more bottom end with the injection than it had with the dual teapots.
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By Joe-JDC - 4 Years Ago
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To get better fuel mileage, there are several common sense things to think about. Higher compression will help mileage if you can keep it out of detonation, weight of vehicle, gear ratio in differential, fresh differential lube, radial tires vs bias ply tires, tire pressure, front end alignment, wheel bearings packed and tightened correctly, brakes adjusted properly, driving technique for starts, tune-up, distributor re-curved, clean air filter, good performance oil (10W-30), cubic inches always make a difference, headers, dual exhausts(even type of muffler will affect mileage), driving with lights on/off, AC, PS, alternator vs generator, clutch fan/flex fan, vehicle lowered and stabilized with good shocks/sway bars. With carburetors, it is suggested to accelerate fairly briskly to the speed limit and back off, with fuel injection, a slow steady increase in speed gives best mileage. Windows rolled up with AC on is best if you have it, for mileage. And last of all, a clean car actually moves through the air easier at speed. My brain is tired, so you may have some more you feel is important to good fuel mileage. Joe-JDC
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By 312YBlock - 4 Years Ago
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While we’re on the subject of gas, just filling my 55’s tank is a crap shoot with lack of back pressure causing gas to overflow. Has anyone come up with a circumvention?
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By Dobie - 4 Years Ago
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I've found that most of the time if I stick the nozzle in the filler neck as far as it will go the nozzle will click off before any gas spits back. This does however depend on how sensitive the nozzle's back pressure sensor is. If you want to get the tank completely full you'll need to squat down and watch. When you can see gas starting to come back up into the filler neck stop pumping.
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By 55blacktie - 4 Years Ago
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Isn't that cam too big for 2.73 gears? What is its RPM range? I chose a cam/w 214 duration @ .050 because I have 2.72 gears behind a C4. The RPM range is 1800-5000, 2200 @ 65 mph. The wide-ratio Dynamic Racing Transmissions gear set has a 2.90 1st and 1.60 2nd. 3rd still 1:1.
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By DANIEL TINDER - 4 Years Ago
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312YBlock (6/4/2021)
While we’re on the subject of gas, just filling my 55’s tank is a crap shoot with lack of back pressure causing gas to overflow. Has anyone come up with a circumvention?
I used to watch and listen (instead of trusting the pump auto-shutoff), and fill until I could see gas in the filler-neck. Bad idea, since my tank’s neck must leak now at the attachment point. If I do that and drive straight home from the gas station, the garage will stink of gas next day.
Since the pump usually shuts off before the level gets high enough to splash, I trust it now, but do watch in case I have to wipe-up any spill.
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By 55blacktie - 4 Years Ago
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I will no longer set the pump handle or leave any vehicle unattended while pumping gas. I made the mistake of setting the pump handle a few years ago, while gassing up my motorcycle in Bishop, CA. The pump failed to click off, spewing gas all over my motorcycle and onto the ground. Upon stopping the pump, I immediately went into the station and told the attendant about the spill. The attendant wasn't concerned. Although my motorcycle had fuel injection, it wouldn't start. After letting it sit for a while, it still wouldn't start. There was a garage nearby that provided a length of hose with which I siphoned some gas from the over-filled tank. I didn't enjoy the taste of 10% ethanol which, by the way, is kind of sweet, but I don't recommend it. I was then able to start the bike. I can only conclude that over-filling the tank must have caused vapor lock.
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By Just Brian - 4 Years Ago
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1954 Ranchwagon, 292 600cfm 4 barrel, don't know about cam oversize etc, 4 speed, don't know diff ratio, 15" tires doing around 2800rpm at 65-70 miles per smile. Wouldn't know and don't care what mpg I'm getting. It's the smiles per mile that matter. I run 95 octane which is around $2.36ltr or $8.50 US gallon here in New Zealand. That's why I run smiles per mile.
Brian
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By Florida_Phil - 4 Years Ago
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I'm 74. The cheapest gas I can remember was 18 cents a gallon during a gas war. When we were in high school, regular gas averaged about a quarter a gallon. I have no idea what my TBird's gas mileage is. When I need gas, I always put the same $20 worth in the tank. When someone asks me the price of gas? I tell them it's $20. 
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By 57RancheroJim - 4 Years Ago
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I had to laugh at the people on the east coast that were crying about gas reaching $3 a gallon when the pipe line shut down. Come to California and we will give you something to really cry about. Filled the Ranchero the other day and it wasn't completely empty and still cost $65.
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By DryLakesRacer - 4 Years Ago
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Our 56 gets 11 with all in town stop to stop driving, basic 292 with 2.74 rear gear and a cruise-o. This last tank was 75% freeway and it definitely made a difference getting 14.7. I’m sure if I hit the road 15+ is doable. I’ll always feel the earlier automatics are mileage killers. Even without an AOD the torque converter in a C4 is more efficient than the early transmissions.
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By DANIEL TINDER - 4 Years Ago
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57RancheroJim (6/5/2021)
I had to laugh at the people on the east coast that were crying about gas reaching $3 a gallon when the pipe line shut down. Come to California and we will give you something to really cry about. Filled the Ranchero the other day and it wasn't completely empty and still cost $65.
Yes, rather galling when filling the tank of my ‘grocery-getter’ SUV costs more than I paid for my first car (‘53 Merc HT)!
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By pintoplumber - 4 Years Ago
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Back when we were racing in Ohio at National Trail, and gas was around $4.00 a gallon, I filled up to come home. The pump shut off at $75.00. I put the card in for another $75.00. It was almost full so I didn’t try again. Gotta love those old suburbans with the 42 gallon tank.
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