Very impressed with gas mileage

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I check my gas mileage in my daily driver every tank. I was taught this by my friend's father 30 years ago, as an early indicator of if the engine was out of tune, brakes dragging, tire pressures low etc.

I reset the trip meter on the odometer at the gas station, fill to the 2nd click, and then drive away. Divide the miles by the gallons and bingo.

If I've had one long trip to the city it's usually around 32 mpg. If not, around 25 mpg for that tank of gas.

In reality I'd know there was an issue from the low miles on the trip computer but I still calculate it out anyway.
 
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What's the standard deviation and confidence levels with a sample size of one?

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the 1 thing that makes biggest difference in mpg will always be the driver! i get decent highway and city millage but get my best out on back country roads between 45 and 55 mph! not lugging it but not turning it up ether, for best mpg drive like theres a egg between your foot and gas peddle, and drive in a way you hardly need to use your brakes!
 
dirty white boy said:
the 1 thing that makes biggest difference in mpg will always be the driver! i get decent highway and city millage but get my best out on back country roads between 45 and 55 mph! not lugging it but not turning it up ether, for best mpg drive like theres a egg between your foot and gas peddle, and drive in a way you hardly need to use your brakes!
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Or use a vacuum gauge
 
Bewy said:
They had similar trials here & the Slant won from memory. Not hard to see why..... The long runners on the Slant [a] improved low end tq & evened up the runner length. The two other contenders were the local Holden & Ferd inline sixes. The Ferd in particular was about as inefficient for power & economy as you can get......The intake manifold resembled a 2 .5 ft length of water pipe with runners running off at 90*.
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The sixes were designed for economy. I believe the Holden and American six intakes were similar. They functioned well enough to get air/fuel to the cylinders but were not as good as the slant six manifolds. The Ford design was about like someone with a 4" rectum crapping in a toilet with a 3" sewer pipe. You could sort of get it through but that is about all you could admit to.
 
RustyRatRod said:
While I will certainly agree it is entirely possible to do it on one trip, that is not the correct way to figure fuel mileage. Fuel mileage is calculated over time with many different trips and then averaged together. You cannot just take one trip and decide you're getting 28MPG. That's not how it works.
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Kind of like driving from Calgary, Alberta to Edmonton, Alberta, about 200 miles and then doing the mileage calculation again on the return trip. Always get better fuel economy driving from Calgary as you drop about 1,000' altitude. Driving to Calgary you climb that 1,000'.
 
RustyRatRod said:
No, you cannot average ONE trip. It doesn't work that way. Go look at any window sticker. It states MPG as an average. That's always how it's been calculated. Go back and look at all the responses here. Mine was the one who called you a liar the LEAST and yet you go off on me? How bout screw you and the horse you rode in on? You just made the list.
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:lol:
 
I got 18 with a 67 383, 2:94 and 4 speed cross country from Ca. to Mo. with a GOOD engine
I have got 25 with a 71 Duster 225 slant 3:23 4 OD with a good engine.
But I drive like grandma some days with the slants!
 
I drove my 63 falcon 144, 3 speed manual, completely original except for tires from Irwindale drag strip to Tucson Az and back for the zip tie drags a few years ago. 2 people, loaded with tools and some spare parts and averaged 27.6 mpg for the whole trip, there and back. 988 miles interstate and a little driving around Tucson while there. I couldn’t believe it. For the next year I kept track of the mileage driving it semi daily back and forth to work and around town. All gps logged. For the year total average mileage was 24.1. Pretty good for an old POS ford sixer.
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I have a feeling the gas pump just shut off before the tank was full. Either that or the car has a serious OD gear in it.

I daily drove a slant for over 100k miles and did every gas mileage mod under the sun and averaged 20-21mpg if I didn't get on the gas hard. That was with a 904 trans. Best I ever got was 23mpg a few times but I chalked that up to the tank most likely not getting full enough.
 
Keep checking it. You'll get your own average over time. Some can rock mpg, others have not a clue. Do you have a vacuum gage? Can you hold the gas pedal steady? Can you coast down hills, use momentum for getting up the next hill? Do you brake coming to a stop? My 64 Barracuda 273 TQ 4 speed would average 25 mpg on a midwest 300 mile stretch between fill ups, odometer dead on. With a 170 slant 6 two barrel high 20's all day long, I'd call it 30mpg on a good 300 mile run. Sounds like you got a good drive train in that car.
 
pearljam724 said:
I’ve owned several A and B body Chryslers. All with small blocks. I just bought a superb condition, 2 owner 72 Scamp with a slant 6 with 60k original miles. I just returned from a 200 mile trip with that Scamp and averaged 28 miles per gallon !!!
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My 11/1 367 did that with a [email protected] cam, all be it with a final drive of 3.55 x .71 x .78= 1.97 ................... and still managed 106 in the quarter.
Actually it did better than that.
If you had put this thread in the /6 forum, I wouldda not said anything, cuz I'm really not an azzole.. and Not a slanty hater.
 
pearljam724 said:
If any of you are calling me a liar.
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I totally believe you man,
But I'll do you one better; I take my own gas along, and gas-up on the fly, and then I call it point to point so there is no way of "interpreting" the results.
My slanty's get tuned up until they bear fruit, and if they don't, I take 'em apart, find out why, then make a better combo out of 'em.
If you want to get an idea of why yours is particularly thrifty, Do these things;
1) a warm compression test, and
2) check your total cruise timing (at whatever speed you were traveling), including any vacuum advance it was getting.
3) Find a stretch of fairly flat, level, hardtop, then take your car up to cruising speed. Let it settle, then put it in neutral and let it coast down, for exactly half a mile. Record the time it took. Go find an on-line calculator that can tell you how much horsepower that your particular chassis is sucking just in friction. IIRC the calculator also needs to know the weight of your car, obviously with you in it.
Just for comparison, my Barracuda takes close to a mile to coast from cruising speed to a stop. This was not that easy to achieve. But if yur getting that high mileage, then yours should be close to mine.

Don't let the guys upset you, I think a lotta guys tend to think that things that they believe to be impossible, truly are impossible.
I'm not that kind of guy, and so I can say that I totally believe that 28.x mpg is totally possible. I believe MORE is possible, so
I believe you.

Check this out:
If your chassis requires only 30 hp to cruise 65mph, the math says this would take about 30 x .5 =15 pounds of fuel per hour at the absolute most, say at 12.5 AFR. A gallon of gas weighs about 6 pounds, so
15 pounds is, 15/6=2.5 gallons. thus 65miles traveled/2.5gallons=26 mpg, and you haven't even leaned it out yet... !
I believe you
BTW
Boys
Cubic inches has nothing to do with this formula
If your 273 67 Dart, or
your 367 68 Barracuda,
or your 440 New Yorker
or whatever,
takes 30hp to cruise 65 mph, then, the formula would generate the exact same numbers.
The trick is, to get the chassis to require only 30hp to cruise 65mph.....
To make this test even more accurate
Leave the trans in gear while coasting down.
Now the formula will include the friction in both the engine and the trans.
Now the big dogs are gonna show their difficulty.
Now the tiny-piston/super long-stroke 225, will show the merits of it's design.
Now that od will show it's worth...... on decel !
I believe you,man
 
Do like Chrysler engineers did, they mounted a gallon cylinder on the car to gravity feed the gas hose to the carb.
 
So if the the Feather Duster could get 35-36 mpg, then why couldn't a slant without A/C and PS get 28 and low milage? Sure it could
 
All I've ever seen , read, or heard about the Feather Duster had all the facts except one, I've never known of a true MPG test by a recognized authority. Please someone, prove me wrong
 
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