Mileage
- Thread starter jrx347
- Start date
well, I have a computer simulator which calculates field miles per gallon given some basic details. I've used it to forecast different miles per gallon for different engine combinations. And then backed it up by realworld testing.
Generally, a 28% overdrive ratio gives a 9% fuel consumption improvement in the field on a 4 cylinder car. A 50% over drive can give 15% more economy on the open road on an I6. Automatic Fords usually have a lower numericsl, higher geared diff than manuals, and taht makes open road milage similar to the old non overdrive 3 and 4 speed gearboxes. But a 5 speed T5 or AOD with a lopeing overdrive can save 15% easily, maybee more, so the stock figures can vary a lot.
So I know that you could pick up 11 to 25% better fuel figures with a 3.08/srod than the C3 or C4 2.73:1 diff BV code Fairmonts when babied. But having 4 to 5% more power at the rear wheels in the real world, you'd probably use the extra performance of a manual and it would probably cost at the gas pump.
There are many factors for mileage.
Power to weight ratio
Engine tune (Idle speed influences, ignition, HP per liter)
Gear ratio, tires, and aerodynamics
Climate (warmer climate uses less fuel)
Driving style (getting optimum mileage takes skill)
Terrain (flat terrain gets a lot better mileage than hilly terrain)
I use the EPA constant 55 mph highway and constant 30 mph city estimates from the LA basin test, they are found only for post 1979 cars. It was an electronic dyno test, so thats why the EPA used it, and it is so accurate, you can pick the percentage improvment a manual has over an automatic, or even the differences a heavier and boxier body has over a lighter, smoother one. Or the influence of a diff ratio.
I have an I6 81 3.3 Mustang Hatch, a 92 hp low efficiency car with a Revised EPA US Highway/City rating in California spec C3 auto form of
City:18 MPG (U.S.)
Highway:26 MPG (U.S.)
Combine:22 MPG (U.S.).
The average cold running city figure of 10.3 US mpg in San Francisco like hills of Dunedin, open road warm running best of 17mpg at 62 mph average open road speed, but normally 53 to 73 mph due to traffic flows and grades of up to +/-12%. My overall average is therefore 13.7 mpg vs. the 22 US mpg ideal for the LA basin test.
Although 21 US mpg is what I get regularly on our steep graded coarse chip roads with an average speed of 62 mph.
Economy on any Fox I6 was great while ambeled along, but poor when used hard, basically due to the wide ratio gearbox. Using an 82 SROD from the 2-BBL GT means the ratio spread is wider, as all SROD 3.3's ran a 3.08:1 diff and 0.81 top. The V8 SROD has a 0.70:1 top and taller first and second gear ratios.
Stock LA Basin 7 mile CAFE millage numbers weren't released for the 4 speed Fairmont, as the option of SROD was withdrawn, but the Mustang/Capri 4speed it was rated at 20 mpg City and 30 Highway, with 23 mpg composite, and the EPA Revised were 18, 28 and 22 respectively. In practice, it could be great or lousy just based on driving style. 16 to 17 is common when not concentrationg on good mileage, but 21-22 is easily within reach in split city and highway conditions
http://www.aboutautomobile.com/Fuel/1981/Ford/Mustang
Compared to the stock 2.73:1 ratio Fairmont auto, http://www.aboutautomobile.com/Fuel/1981/Ford/Fairmont
you could pick up 11 to 25% better fuel figures with a 3.08/srod than the C3 or C4 BV code Fairmonts. BM code Mustangs were around in reasonable numbers, but were only high mount Blue engines.
http://www.coverbrowser.com/image/motor-trend/326-9.jpg
http://www.ascmclarencoupe.com/Literature/Magazines/MotorTrend-March1981_1.jpg
http://www.ascmclarencoupe.com/Literature/Magazines/MotorTrend-March1981_2.jpg
But you can calculate it for any pre 1983 passenger car without a wind cheeter body.
The formula for best miles per gallon at an average speed of 62 mph is based on the from the Index of Thermal Efficiency, found in French Grand Prix and English RAC litrature by Hodges,
and revised in 1980 for the Australian Total Economy Run. http://www.snooksmotorsport.com.au/inde ... &Itemid=39
It eliminates different frontal areas, tire drag and variable drag co-efficents, and is based on a coarse chip road surface, so it works for non wind cheeter boxy Mustangs, Falcons and sedans and wagons driven in non freeway conditions.
mpg@62mph = 1/(140 L/M act + 0.006W + 5)*100*2.2588
3.540062
Where: L = the engine swept volume in liters, calculated as follows:
Bore in mm*Bore in mm*Stroke in mm*No of Cylinders*0.78543691
M act = mph per 1000rpm in the highest available gear, using normal driven wheel tire
placard details as follows:
(Tire section*Aspect ratio as decimal)+(Tire section*Aspect ratio as decimal)+Wheel diameter in inches*25.4
1.022
Then multiply the result by 3.141 * 60, then divide by the diff ratio, and multiply by the top gear ratio
Note: If auto,atic, 15% allowance for slippage was allowed for automatic transmissions,
and the result of M is mulitiplied by 0.85.
This is because a T5 and 7.25 to 9" diff takes 26.5% power from the engine,
a C4 and 7.25 to 9" diff takes 31%. Difference in power loss from a manual to an automatic is usally 0.85
W = weight of the vehicles in pounds, plus the ballasted weight of the
one driver and same weight passenger (200 +200 pounds and full tank of advertised fuel US Gals times 6.073 pounds).
Divide by 2.2046223
Those figures above for
the 1981 3.3 Mustang SROD 4 speed , 3.08:1 diff, 0.81:1 top gear(overdriven)= 28.5 US mpg at 62 mph
the 1981 3.3 Mustang C3 Auto 3 speed , 2.73:1 diff, 1:1 top gear =24.7 US mpg at 62 mph
the planned 1981 4.1 Mustang AOD 4 speed , 2.73:1 diff, 0.67:1 top gear = 27.2 US mpg at 62 mph
all come from the above formulae, and it works.
Generally, a 28% overdrive ratio gives a 9% fuel consumption improvement in the field on a 4 cylinder car. A 50% over drive can give 15% more economy on the open road on an I6. Automatic Fords usually have a lower numericsl, higher geared diff than manuals, and taht makes open road milage similar to the old non overdrive 3 and 4 speed gearboxes. But a 5 speed T5 or AOD with a lopeing overdrive can save 15% easily, maybee more, so the stock figures can vary a lot.
So I know that you could pick up 11 to 25% better fuel figures with a 3.08/srod than the C3 or C4 2.73:1 diff BV code Fairmonts when babied. But having 4 to 5% more power at the rear wheels in the real world, you'd probably use the extra performance of a manual and it would probably cost at the gas pump.
There are many factors for mileage.
Power to weight ratio
Engine tune (Idle speed influences, ignition, HP per liter)
Gear ratio, tires, and aerodynamics
Climate (warmer climate uses less fuel)
Driving style (getting optimum mileage takes skill)
Terrain (flat terrain gets a lot better mileage than hilly terrain)
I use the EPA constant 55 mph highway and constant 30 mph city estimates from the LA basin test, they are found only for post 1979 cars. It was an electronic dyno test, so thats why the EPA used it, and it is so accurate, you can pick the percentage improvment a manual has over an automatic, or even the differences a heavier and boxier body has over a lighter, smoother one. Or the influence of a diff ratio.
I have an I6 81 3.3 Mustang Hatch, a 92 hp low efficiency car with a Revised EPA US Highway/City rating in California spec C3 auto form of
City:18 MPG (U.S.)
Highway:26 MPG (U.S.)
Combine:22 MPG (U.S.).
The average cold running city figure of 10.3 US mpg in San Francisco like hills of Dunedin, open road warm running best of 17mpg at 62 mph average open road speed, but normally 53 to 73 mph due to traffic flows and grades of up to +/-12%. My overall average is therefore 13.7 mpg vs. the 22 US mpg ideal for the LA basin test.
Although 21 US mpg is what I get regularly on our steep graded coarse chip roads with an average speed of 62 mph.
Economy on any Fox I6 was great while ambeled along, but poor when used hard, basically due to the wide ratio gearbox. Using an 82 SROD from the 2-BBL GT means the ratio spread is wider, as all SROD 3.3's ran a 3.08:1 diff and 0.81 top. The V8 SROD has a 0.70:1 top and taller first and second gear ratios.
Stock LA Basin 7 mile CAFE millage numbers weren't released for the 4 speed Fairmont, as the option of SROD was withdrawn, but the Mustang/Capri 4speed it was rated at 20 mpg City and 30 Highway, with 23 mpg composite, and the EPA Revised were 18, 28 and 22 respectively. In practice, it could be great or lousy just based on driving style. 16 to 17 is common when not concentrationg on good mileage, but 21-22 is easily within reach in split city and highway conditions
http://www.aboutautomobile.com/Fuel/1981/Ford/Mustang
Compared to the stock 2.73:1 ratio Fairmont auto, http://www.aboutautomobile.com/Fuel/1981/Ford/Fairmont
you could pick up 11 to 25% better fuel figures with a 3.08/srod than the C3 or C4 BV code Fairmonts. BM code Mustangs were around in reasonable numbers, but were only high mount Blue engines.
http://www.coverbrowser.com/image/motor-trend/326-9.jpg
http://www.ascmclarencoupe.com/Literature/Magazines/MotorTrend-March1981_1.jpg
http://www.ascmclarencoupe.com/Literature/Magazines/MotorTrend-March1981_2.jpg
But you can calculate it for any pre 1983 passenger car without a wind cheeter body.
The formula for best miles per gallon at an average speed of 62 mph is based on the from the Index of Thermal Efficiency, found in French Grand Prix and English RAC litrature by Hodges,
and revised in 1980 for the Australian Total Economy Run. http://www.snooksmotorsport.com.au/inde ... &Itemid=39
It eliminates different frontal areas, tire drag and variable drag co-efficents, and is based on a coarse chip road surface, so it works for non wind cheeter boxy Mustangs, Falcons and sedans and wagons driven in non freeway conditions.
mpg@62mph = 1/(140 L/M act + 0.006W + 5)*100*2.2588
3.540062
Where: L = the engine swept volume in liters, calculated as follows:
Bore in mm*Bore in mm*Stroke in mm*No of Cylinders*0.78543691
M act = mph per 1000rpm in the highest available gear, using normal driven wheel tire
placard details as follows:
(Tire section*Aspect ratio as decimal)+(Tire section*Aspect ratio as decimal)+Wheel diameter in inches*25.4
1.022
Then multiply the result by 3.141 * 60, then divide by the diff ratio, and multiply by the top gear ratio
Note: If auto,atic, 15% allowance for slippage was allowed for automatic transmissions,
and the result of M is mulitiplied by 0.85.
This is because a T5 and 7.25 to 9" diff takes 26.5% power from the engine,
a C4 and 7.25 to 9" diff takes 31%. Difference in power loss from a manual to an automatic is usally 0.85
W = weight of the vehicles in pounds, plus the ballasted weight of the
one driver and same weight passenger (200 +200 pounds and full tank of advertised fuel US Gals times 6.073 pounds).
Divide by 2.2046223
Those figures above for
the 1981 3.3 Mustang SROD 4 speed , 3.08:1 diff, 0.81:1 top gear(overdriven)= 28.5 US mpg at 62 mph
the 1981 3.3 Mustang C3 Auto 3 speed , 2.73:1 diff, 1:1 top gear =24.7 US mpg at 62 mph
the planned 1981 4.1 Mustang AOD 4 speed , 2.73:1 diff, 0.67:1 top gear = 27.2 US mpg at 62 mph
all come from the above formulae, and it works.
jrx347":2opf2trm said:
For your 1966 Mustang coupe, 200 six, c4, 279 rear axle, my workings are:-
24.3 us miles per gallon at 62 mph
With that axle ratio, a 4 cyl T5, 29.9 mpg at 62 mph
On http://www.automobile-catalog.com/model ... _1gen.html
they list http://www.automobile-catalog.com/car/1 ... matic.html, they get 17.8 US mpg with a 3.20:1 four speed, while I get 24.7 mpg
And 17.0 miles per gallon with auto and 2.83:1 gears, while I get 24.1
See http://fordsix.com/forum/viewtopic.php? ... 35#p544435
Ks65Mustang
New member
Don't have a C4 but with my stock 3 speed, in a stock 65 mustang I get 26 mpg overall.
edgewood bronco
Well-known member
I've ran a 78 zephyr with a 200 and c4, all stock except for removal of the catalytic converter and EGR stuff, and I got 20 on average. At 65 mph on long road trips, I have gotten as high as 22. I find that on any vehicle once you top 60 - 65, your mileage suffers; that includes my 02 accent (I admit: I commute in a ricer) and my 62 F100.
xctasy, your formulae are intriguing, I'm going to have to play with that some time.
Best,
Andy
xctasy, your formulae are intriguing, I'm going to have to play with that some time.
Best,
Andy
Mileage may vary
I have driven many miles under widely varrying condition.
I drive a 69.5 Maverick with a 170 and a 3 speed manual transmission.
I have gotten as low as 13 mpg on a 3 mile one way comute. I removed the fan and blocked the partly radiator in an attempt to reach opperating temperature as soon as possible. This was in all flat driving in the Bay area of California.
I have gotten a one time high of 39 MPG in Arizona on rout 10 driving from Phonix to Tucomcary in the 80's with a freshly tuned engine.
My son gets between 22 to 26 MPG right now on a 15 mile express way one way comute in the bay area.
Bottom line, Mileage depends heavily on how you drive, where you drive, the length of the trip and weather conditions.
If you can't keep your foot out of it, like me, your mileage will suffer.
Goodluck
PS my son is a lot easier on the throttle then I am.
I have driven many miles under widely varrying condition.
I drive a 69.5 Maverick with a 170 and a 3 speed manual transmission.
I have gotten as low as 13 mpg on a 3 mile one way comute. I removed the fan and blocked the partly radiator in an attempt to reach opperating temperature as soon as possible. This was in all flat driving in the Bay area of California.
I have gotten a one time high of 39 MPG in Arizona on rout 10 driving from Phonix to Tucomcary in the 80's with a freshly tuned engine.
My son gets between 22 to 26 MPG right now on a 15 mile express way one way comute in the bay area.
Bottom line, Mileage depends heavily on how you drive, where you drive, the length of the trip and weather conditions.
If you can't keep your foot out of it, like me, your mileage will suffer.
Goodluck
PS my son is a lot easier on the throttle then I am.