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what are your MPG's?
#1
This weekend we went took a long ride with the car, 207 miles. and I was amazed at the MPG's I got.

I topped off the tank when we left, and I topped off when we got back, 9.5gal and traveled 207 miles, that comes out to almost 21+ MPG's!!! 98% highway.

Stock 302, Stock 2100 Carburetor, Stock FMX trans, and Stock 2.79 Rear end, Dual Exhaust.

[Image: 2zem9nk.jpg]
Iyman
1972 Mustang convertible run_horse  
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#2
Show off. Tongue Good job though! What speed were you going on the highway?

Seems like I get between 9 - 12mpg but I've not been easy on the throttle after the engine is warmed up. I should do a Myth Busters experiment. Wink I've not driven it much at all this year though. Undecided

I keep track of my mileage at http://www.fuelly.com/car/ford/mustang. My 4-speed car is the only 71 in the group. It would be cool to see others on here track on fuelly then we could see what the real world mpgs look like.

[Image: 386_07_10_13_5_58_42.jpeg]
My Mustangs:
71 M-code Mach 1, Medium Blue/White Sport, 4R70W, 3L50, Factory Ram Air.
72 Q-code Mach 1, Pewter/Black Sport, 4-spd, 3L25.
65 Convertible, Britney Blue/White/White, more modified than original.
05 Convertible, Legend Lime/Tan/Tan, future classic??
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#3
90 of the miles were at about 50 MPH, and the Rest was at about 65 - 70MPH.

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Iyman
1972 Mustang convertible run_horse  
Visit the Mustang Car Club of New England Facebook Page

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#4
i've gotten 25 mpg highway on a long trip as well. at the time i had a taller ratio 2.75:1 this was on my 351 cleveland also.

what murders MPG is the accelerator pump/power valve, that is why a light pedal slow acceleration increases MPG. When you stomp on it 30cc of fluid goes right into the engine instantly. additionally the Power valve will open and dump like 1/2 a gallon into the engine. Plus the cruise jets are running and the transition slot is driping fuel.

so every time you get on the pedal, first your dumping pump shot into the engine from the accelerator pump to compensate for lean condition, the engine vacuum then drops and the power valve kicks on, so 3/8 or 5/8 tube worth of fuel is dumping into the engine for as long as you hold the pedal down. plus the cruise jets are flowing down into the engine. that is why for street driving red light to red light you get like 4-12 mpgs even modern cars can get like 6-9mpg. It was a joke on some cars that you reved the motor and watched the fuel gauge drop 1/8 at a time, and that was actually true on the 1970s jeep cherokee where in offroad configuration you got 1-2 mpg and 4-6 on the highway, the dodge power wagon was just as bad also.

most guys want more power so they also increase the carb CFM and increase the exhaust size, flow more in, flow more out equals more power and drop the MPG even more. that is in addition to what Cubic inch the engine is.
there is more to it also the heads on the engine and intake valve to exhaust valve size ratio has a tremendous effect on MPG. i read somewhere the closer you get to IN/out valve ratio being 1:1 the better the mpg.

this is why in the fuel crises days the Inline 6 was the best option for 71-73, coupled with a single pipe exhaust and 2 barrel carb and the tallest 2.75:1 ratio you could find, and it was possible to get 35MPG in a 71-73 mustang on the highway. and street mpg would be in the 9-12 range, some people would advance the timing and increase throttle rpms and could even get 16mpg on the street with a light foot and learning how to roll the car with a higher idle.

This is why the vacuum advance is so critical and it is the least understood part of the motor for many many engine builders. they all think those are evil and they always disable them and run the engines on mechanical advance only.
basically the vacuum advance advances timing depending on load in addition to the mechanical advance. that means as you accelerate the load is increased the vaccum advance advances timing which raises engine RPMS and gets you to your desired Speed faster meaning your lighter on the pedal without you realizing it. it also helps the motor burn the fuel better by adjusting when spark occurs. so the engine runs more efficiently. just tuning a distributor for the street could bump MPG 10 or more.

so lean out the motors just shy of detonation install a smaller diameter exhaust instead of 3" or 2.5" you go to 2.25" and the increased back pressure and carb double dip from resonance will increase MPG by itself. but the seat of your pants may feel slower.
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#5
Hmmm. 35 MPG You are sure making a good case for the inline 6 for cruisin!

Ray

1971 Boss 351  
1972 Q code 4 speed convertible 
1971 Mustang Sportsroof  351-2V FMX 
1973 Mach 1 (parts car)
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#6
Even though I've greatly increased the power output of my 351C, I'm thinking the AOD and 3.00:1 rear gears should offer up some pretty decent fuel mileage numbers - providing I can keep my foot out of it, that is. My speculatory 'fuzzy math' has me in the 21-22mpg range based on 'normal' driving.

I know my 1997 Dodge Ram 1500 4x4 gets an average of 12mpg during 'normal' driving for me (a mix of 1/3 regular street driving with about 2/3 'freeway' driving). So if I can squeeze out over 20mpg during 'normal' driving conditions, it'll be close to double my overall fuel economy.

I also expect to improve it even further after awhile by installing an Edelbrock E-Street TBI set-up. But, that's down the road - gotta get it 'on the road' first. Wink Big Grin

Eric

[Image: mach1sig2.gif]
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#7
Mister 4x4;130488 Wrote:Even though I've greatly increased the power output of my 351C, I'm thinking the AOD and 3.00:1 rear gears should offer up some pretty decent fuel mileage numbers - providing I can keep my foot out of it, that is. My speculatory 'fuzzy math' has me in the 21-22mpg range based on 'normal' driving.

I think you're in the ballpark Eric. With a 26" tire height you'll be at 1800 rpm at 70 mph - a great rpm for mpg. The downside is the AOD's 2.40 first gear might be a tad slow off the line with a 3.00:1 rear but you'll be able to hit 65mph in first gear at 6k rpm. Big Grin A normal 2500 rpm shift point would be 27mph from first gear and 44mph from second to third gear.

[Image: 386_07_10_13_5_58_42.jpeg]
My Mustangs:
71 M-code Mach 1, Medium Blue/White Sport, 4R70W, 3L50, Factory Ram Air.
72 Q-code Mach 1, Pewter/Black Sport, 4-spd, 3L25.
65 Convertible, Britney Blue/White/White, more modified than original.
05 Convertible, Legend Lime/Tan/Tan, future classic??
  Reply
#8
Don65Stang;130506 Wrote:I think you're in the ballpark Eric. With a 26" tire height you'll be at 1800 rpm at 70 mph - a great rpm for mpg. The downside is the AOD's 2.40 first gear might be a tad slow off the line with a 3.00:1 rear but you'll be able to hit 65mph in first gear at 6k rpm. Big Grin A normal 2500 rpm shift point would be 27mph from first gear and 44mph from second to third gear.

Then that would be the downside of the FMX as well, since the AOD and FMX share the same gear ratios... until the AOD kicks into Overdrive (which the FMX does not have). Wink

That's one reason I haven't been so worried about changing out the rear gears - the car essentially came this way from the factory (minus the Overdrive, though). Factory 245hp 351C-2V 'H-code,' FMX, 3.00 seemed to be 'OK' out of the box... I'm thinking it should be pretty awesome with 400-ish horsepower. Big Grin

Worse-case scenario: I swap the 3.00s for 3.55s.


Sorry for 'jacking the thread... but at least it's relevant. Cool

Eric

[Image: mach1sig2.gif]
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#9
With my 460 ,i figured it would be too depressing to even try to figure that out!Tongue

[Image: 1_11_01_14_4_00_47.jpeg]
460 , Edelbrock Performer carb. + intake , 204 / 214 cam , Pertronix Flamethrower 2 billet dizzy + coil , Crites long tubes , C6 .









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#10
Kermit 460;130519 Wrote:With my 460 ,i figured it would be too depressing to even try to figure that out!Tongue

If you have anything close to highway gears (3.55 or taller), it might not be as bad as you think. Cool

Eric

[Image: mach1sig2.gif]
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