History fuel economy assumptions

ive been doing a lot of research lately into fuel economy, a subject rarely touched in hotrod forums.

anyway, from what i learned, lets compare a modern cars fuel economy with hotrods, muscle cars, etc. a modern ford fusion is rated at 20/29, and these are often exaggerated figures that look good on paper to sell cars to a fuel concious market

in comparison, pony and muscle cars of the late 60s and early 70s with stock, often small block engines would make something like 17-18mpg city, a mere 2mpg shy of a modern compact with a small four cylinder engine

physics behind this would suggest a larger engine with more torque does less work to get a vehicle up to speed, so burns less fuel when comparing the sizes of the engine

since the thermal efficiency of the internal combustion engine is pretty much maxed out by its inherent design that there isnt much fuel economy difference between a modern compact and a stock muscle car, i have to ask... why do people assume these old cars are so much worse off when it comes to driving regularly?..

perhaps this is just automotive marketing.. if you make the general population believe theyll go broke driving an old car, and that buying a new car will "pay for itself" they obviously sell more new cars... is this where the assumption that old cars are all "gas guzzlers" comes from?

a stock pony/muscle car vs a modern car getting only a couple miles per gallon less than a modern, supposedly fuel efficient compact. i would rather take that 2mpg less and actually drive something fun, entertaining, and just plain beautiful, and the research leads me to believe my pocket wont be too sad either.

this does not include modern engine upgrades which will increase the fuel economy of these older cars even further, new carb, valve, piston designs, etc which will increase economy even more

anyway, id like to hear your opinions on this statement, and hear what you guys think about a general assumption that youll go poor simply by driving these things?.

 

well I'm not sure but I know that my old VW jetta diesel would go two weeks between fillups...No crap two weeks, my new F150 goes 2 days....

 

Well, Justin I have no idea of how old you are and if you were around when those super cars and their small block brethren were new but the gas mileage for most of them wasn't great. My 69 Old Cutlass S with a 310 hp 350R Muncie close box and 3.42 Posi got 15.5 on a road trip with me driving it an 17 with my buddy driving it on the next tank. That was with him running at 70 on the freeway across Arizona headed from Fort Hood Texas to LA. In town I would guess it got 13 or maybe 14 but it wasn't too important at the time.
Tuned right and driven right some of the cars from that era could pull decent mileage but nothing close to what these cars get now. I drove a fresh off the showroom floor 84 Corvette 350 automatic from Portland Or to Sunnyside Wa in 84 and averaged better than 24 mpg. That was while not worrying about gas mileage. The 04 Chev full size extended cab 4x4 I put 170 miles on today for work (it's a govt fleet car) got 16.5 running at the 70 mph speed limit. My 71 350 might get 12 if I baby it.

And you can always do what my dad and uncles did when they got together back in the 50's and 60's and just lie about what mileage you got.

You can't put much credence in those old Mobil Gas economy runs where they used to pull incredible gas mileage some times because those guys used every trick in the book including a lot of shutting the engine off and coasting down hill.

 

it just seems to me that a lot of those stock pony cars like the camaro/firebird, mustang, etc actually got really good fuel economy when compared to their big block relatives, and that if rebuilt using modern components (like heads, carbs, pistons) designed for better fuel economy, theyd go pretty close to toe to toe with a modern "efficient" car..

and combining that with the fact theyre easier to work on, more reliable (so many fewer parts to fail) that it wouldnt be such a bad choice even with fuel prices as they are now...

you could even include muscle cars with their small block engine options, like the charger for example with a 383 i dont think would be so bad if rebuilt to be more efficient

 

my kid's 70 camaro with the six/powerglide gets close to 20 in rural driving. My 55 with the blown big block gets around 8 under the same conditions.

That 93 ford crown vic we had several years ago (a big car with a small V8) got around 23.

My wife's Dart used to get around 20 with the original 225/3 speed. Now it gets around 12-14 with a 340/auto.

Her late model full size truck gets 21.

I usually get about 10-12 with my old trucks with big blocks in them.

Most modern cars get at least 25 on the highway, most old full size cars (pre-1975) got about 15. There were exceptions, but not many.

Stick a modern overdrive transmission in an older car, improve mileage 30%. Beyond that, there isn't much you can do that will make a big improvement.

 

My '64 with the 440 and 4.56 rear gears gets 7 or8 around town, (depending on throttle position) and an honest 10 running 70 mph on the freeway. That said, it's more fun than a modern econo box.

 

My '05 pony GT with a 5-speed manual and 3.55's out back averages about 17.5 miles per gallon. My old '91 LX 5.0 with a manual and 3.08's got 12 per gallon. Same with my '96 F-150 5.0 w/4-speed auto and 3.55's out back.. Seems the newer ones are getting better mileage with more horsepower... I can live with that...

 

well when you start talking big blocks, and 4000lb cars from the 40s and 50s, those are seriously horrible on mileage, a 1950s buick roadmaster gets something like 8mpg city... but it is safer than just about any other car on the road, who needs side curtain airbags when youre built like a tank?.. and about as slow as one

now as far as old cars vs new cars go... some efficient V8s in pony cars from the 60s are just shy of some modern four cylinder engines.. which says per cubic inch a well built V8 tends to be quite efficient

that being said the 2.3L pinto engines is a very efficient engine, its actually related as one of the most efficient american made engines out there in its thermal conversion rating

 

heres another question.. modern V8 engine but take off the excessive electronics, and install a good, quality carburator and place it into one of these old cars, what do you suppose fuel economy would be then?

i like some of the features, and designs of modern engines, however i will say they are notoriously unreliable in the sense it seems like every week another sensor has fried, or the cars they put them in you sometimes have to remove the engine just to change the spark plugs.. personally, i like an engine with less to go wrong, and a compartment with room to work in

 

well first off your comparing the best gas milage cars of the 60's to the worst mileage cars of today, so its not really like they are that close. heres how bad the example looks if you take a great mpg car of today, to a bad car of the 60's. ( truck but you get what im saying.

my ol ladys 2008 civic gets 46 mpg. my 66 c10 gets 7-8 mpg.

 

Rule of thumb made up by moi so take it for what it's worth

small block: around 12 city

big block: around 8 city

throw all the money you can at it and you *may* get an extra mile or two in city, I don't think I've ever seen anyone pretend it's cost effective though.

the vast majority of these cars were 3 speed autos or sticks.

Basically, what Squirrel says.

Don't forget, the muscle car engines needed a valve job at least by 40k and were usually leaking, smoking, inefficient s-piles by 80 k.

This is the cue for the guys whose Chevelle got 20 mpg with a 454 and did 250,000 miles without a tune up.

EDIT: FWIW mid 80s Honda CRX HF got mid 40s freeway without an electric motor.

 

I still have the '91.. I just don't drive it much anymore since I dropped a 352 ci roller windsor in it about 7 years ago.. That thing scares me!

 

Fuel economy is a function of many variables. Squirrel hit on the major one with the O.D. transmission that would reduce engine RPM on the highway.

I personally have always been concerned as much with fuel economy as with performance (yes Virginia, you CAN have both); and with one exception (1963 Corvette 327/340) all my vehicles have obtained pretty decent milage. The major issue with the Corvette was the 4.11: final drive ratio.

Current "hotrod" is my shop truck (1968 Ford F-100 w/390 2x4 and 4-speed). Mileage at 70 MPH is about 22 on real gasoline and about 18 on E-10. City driving is much worse; somewhere around 11~12. But mileage with a 16 foot trailer, and 2 400 series John Deere lawn and garden tractors only drops on the highway to about 15 on E-10.

The key is to look at the fuel efficiency curve for the engine. And go have the engine RPM at the valley of the curve (either with rear gearing or transmission gearing) at cruise speed.

The link is to a portion of the "troubleshooting" page on our website:

http://www.thecarburetorshop.com/Troubleshooting.htm#Fueleconomy

Jon.

 

If you pulled the EFI out of a modern V8 and installed an ultra efficient carb, you'd have a boat anchor. No spark = no go. By the way, I've found the EFI cars to be very dependable. The shitty part is when they do go down, few people know where to start looking for the problem.

"Back in the day", it was tough to find any car that would break 20 mpg. I had a Gremlin with 232 and got about 22-24, no one got any better, regardless of what they drove. Lots of people lied about their mileage, guessed, or forgot to add the last fillup on a trip. My buddy did that with a Buick 225. Told me he got over 16 mpg on a long trip. He left town with a full tank, came back with an empty tank. When he filled up and recalculated, it was about 14.

X 2 on the mileage of modern cars. We have an '02 Focus wagon. Zetec engine, 5 speed. Will deliver 33-36 mpg at 65-70 mph. and turns in quite respectable performance.

In the '80's GM did have some V8's that got fantastic mileage. The state had a full sized Pontiac wagon that would routinely give 24 mpg. Was the damndest thing to drive. It would NOT accelerate without dropping down a gear of two, then it would go like a scalded dog. That was just weird. If you were driving along and realized you'd let your speed drop a little, it would have to downshift before you could bring it back up.

Bill

 

spend $40k building a car & worry about fuel mileage? my car is obnoxious loud, rough riding, clutch is stiff, shifter is stiff, exhaust stinks to heaven & gets about 10 miles per gallon - i wouldn't have it any other way - fuel mileage? who cares?

 

"why do people assume these old cars are so much worse off when it comes to driving regularly?.."

Because they have allowed them selfs to become sheep..and they trust...you know who.

and its like any thing else ..if they pound it into your brain for so many years people tend to think its true with out researching for themselfs....lazyness

 

Simple fact is that emission controls suck up quite a bit of fuel economy.

Back in the 80s and 90s where a lawful emissions could be obtained (mostly) by making an engine more efficient, my memory says that "apples to apples" cars got better mileage. IMO, I want to think that in an effort to get "last percent" of pollutants out of the exhaust has cost 10% in fuel mileage, all well worth it for a bureaucrat lacking in any form of common sense...

I think modern cars could do a lot better without this huge burden.

(Remember when VW Rabbits used to get better than 40 mpg on gasoline?)

Anyway, it also does not help that Detroit can't make a Camaro, Challenger, or Mustang that weighs under 4 grand.

That said, my 55 Lincoln does at least as well on gas as my wife's Tahoe and my Silverado...

 

i noticed that about the camaros, chargers, and mustangs being over 4 grand.. i just think to myself, wow, muscle cars with steel bodies weighed an average of around 3k.. but hey, when you have to have power seats, power windows, a 6 speaker system with 2x10 subwoofers, power moon roof, gps, bluetooth.. well it tends to get heavy.. and i wouldnt care about having any of it

 

anyway, from what i learned, lets compare a modern cars fuel economy with hotrods, muscle cars, etc. a modern ford fusion is rated at 20/29, and these are often exaggerated figures that look good on paper to sell cars to a fuel concious market
Exaggerated??? I have exceeded the window sticker fuel mileage on a new 84 T Bird, a new 87 Tempo, a 2000 Lincoln LS, and my wifes 05 LeSaber. All off topic cars, all good daily drivers. The last tank in the Buick was 26.5 with just over 100,000 miles. My built Y block five speed 3:73 gave 15.5 last summer on the way to the salt and back. It also gave 10.1 on one tank. The bottom line, is, with careful driving, a newer car will perform well. And the rod? Build it and drive it. If you want great fuel mileage, buy a Euro spec turbo diesel that gives 76 MPG. Ford has one on sale now in England and Europe.

 

Pure nonsense, Justin.

 

Hell back in the day nobody gave a crap about gas mileage because the gas wasn"t that expensive,now outrageous prices,outrageous repair work ,people want as much as they can get.My 53 with 400 sb turbo 400,373 rear gets 14-16 miles to the gallon,and my old ladies Chevy pickup,2007 350 with aod trannie just gets 18-20.The Government is never going to require auto makers to build cars for gas mileage,look at the tax money they would lose on that one.

 

I've driven a lot of older vehicles as daily drivers. Driving style is a huge varible with those old cars. A newer car I've noticed won't get the same huge difference in mileage between stomping on it and driving like an old lady.

On a similar note I have a large collection of old car magazines plus I've read a lot of old car reviews online from the 50s. The belief that people back in the day didn't care about fuel economy is a bunch of bunk. In Popular Mechanics they would send out owner surveys. Almost without fail everyone would complain about poor fuel economy. Also I've used the BLS inflation calculator and found for the most part gas has averaged about 2.30 a gallon in today's dollars. The era of cheap gas was the late 90s/early 2000s. It was cheaper than any other time in history including the 60s when adjusted for inflation.

Now the most fuel efficient vintage car I had was a 53 Plymouth Cranbrook. It got 30 mpg going to work some 45 miles away. Had a 3 speed with a 218, all stock. I also drove it very conservatively. I've squeeked out 20 mpg out of a 4x4 Ramcharger with a v-8 automatic. My 77 F100 would get 23 mpg all the time (also drove like a snail). I had a 63 Rambler Classic but that didn't get as good as the 77 F100. Right around 22 mpg which was okay but a modern car in it's size class would blow it to the weeds in the mileage department. The 65 F100 I have now is quite hard on fuel. It has a little 240 with a three speed and the best I've gotten was 16 mpg. It is starting to really hurt the ole budget trying to feed it all the time.

 

we all love old cars.

but talking yourself into saying they get better gas mileage than todays cars, is like the loving mom who goes on jerry springer telling everybody her 300 pound 7 year old is healthy.

cars today are safer, run better, and get 3 times as good mpg. but thats not why we drive our old cars so why even bring that up in disscussion?
that being said...

i dont care if my 52 chevy got 3 mpg , id still drive the fucker as much as possible.

 

When I am in the market for a family car/daily driver, fuel economy is extremely important to me. When it comes to my hobby vehicles, fuel economy, or for that matter, emissions don't factor whatsoever.

 

today ,, a good econo-box car will get great gas millage ,, amusing that there is only one person inside .. BUT ,, stick a guy inside who is around 225 lbs . with 3-4 of his buddy's who weigh around the same ( amusing that you can fit them in ) and check the millage then ... try going up a big hill,, see how long it will last .. they will turn into junk quick ..i know ,, i have had a few .... i would rather have a good old car that will pull a lot of weight and have the power to spare ....
and the millage won't be too much different ...

 

Comparing same car sectors, a 2010 Fusion V-6 weighs nearly 1,000lbs more than a 63 4-dr Comet with the 144ci I-6 (non-muscle car) and their mileage would be very similar. Your assumption SB muscle cars got nearly 18 in the city is off the mark, IMO. Driving techniques will garner the best mileage and can beat EPA sticker ratings. The most amazing fact of the current vehicles is the current HP, mileage, and near zero emissions output. Back in the 60s Dodge/Plymouth were the lightest cars, then Chevrolet, then Ford in the full-size segment and mileage would vary by how they were driven. Ford's Mileage Maker 6 with OD got into the 20mpgs in a Galaxie. As for new-wave hot rodding, I'd like to see/do a 2011 301hp 3.7L Ford V-6 (base Mustang) with the new 6R80 6-spd tranny in an early 60s Falcon. Someone has already put the Ford 5.0L Coyote (2011 GT motor) in a hot rod (I think it'll be at SEMA), Rod.

 

Daily driver only vehicle, '49 Chevy 1/2 ton, '56 235, 1-2 bbl Carter- Weber, Fentons, '62 3sp+od, '57 3.90 rear, Thanksgiving 900 mile round trip 17.8 mpg.

 

At present my '31 roadster pulls about 30-32 mpg. It is a future Rod built after being challenged by my mechanic buds. I went w/a '05 Duratec alloy 2.0 DOHC Focus motor, w/Ford COP coils, sensors and a Megasquirt ECU. This motor has aftermarket gear available from Crower, Crane and Cosworth, so for this reason I chose it. Tuning may yield improvements, I'll post any that turn out worthwhile.

 

My wife is now driving her second Ford Focus. It' a 2010. Both got 28 MPH in town. The 2010 has gotten 42.2 on trips to Chicago in uninterrupted traffic with the cruise control on. If we keep it at a steady RPM it's phenomenal! We've checked it several times, and it's very accurate. With our current gas prices here in Central Illinois, it's good news for sure! On the other hand, if I'm that concerned about my hotrod's fuel economy, I'm in the wrong racket! I could care less about 2:79 gear ratioes, AOD's, 31 inch rear tires, and everything else many of us crow about, I just RUN! I've got a very high geared 5 speed & rear end gear in my 27 T RPU, and it gets 18 or better in town, and 22+ on the open road. The trouble is, it's GEARED TOO HIGH! My SBC will never see 3500 RPM's unless I'm running at Bonneville! I'm lugging around enjoying my gas mileage and wearing out an engine with all new internals in it! You can achieve overkill with some of this stuff if you're not careful. Just drive it!...that's what you built it for, Right?

 

I got an honest 21 mpg when I still had the 235/t5. I divided miles traveled by fuel used to fill the tank. pure highway driving kansas city to Salina.

I have done the same with a 2005 nissan, 60 more horsepower, 8 more mpg, loaded with furniture from Ikea in the twin cities, back to KC. air conditioner on, 75 all the way.