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Fuel economy question...

When I drove this car in High School with a 10.5:1 446, Erson High Flow III, Holley 980 3-barrel, and broken gas gauge; I would use 6mpg estimate and fill up every 120 miles. I was a heavy footed teenager that did a good bit of street racing.

In it's current form, I can move the gas gauge by making a full pass. 11:1 605 Hemi, custom grind Comp Roller, Thumper Dominator.
 
13mpg with a 318 2barrel isn’t the greatest but yeah it should be capable of getting up to 20 on the highway. And I mean 20 max if you’re fine tuning everything to the best of its capabilities.
Just out of curiosity, what rpm are you spinning at 65mph?
 
Triplegreen500 said:
No idea, no tach. Factory dash has a (broken, lol) clock. If I find a decent vintage tach at Carlisle I may pick it up...
Click to expand...
Well it might not be spot on but you can figure it out with some math. I got this formula from David Freiburger on Roadkill Garage:
RPM = (mph X gear ratio X 336)/ rear tire diameter
 
fine69 said:
Well it might not be spot on but you can figure it out with some math. I got this formula from David Freiburger on Roadkill Garage:
RPM = (mph X gear ratio X 336)/ rear tire diameter
Click to expand...
So just for example:
(65mph X 2.76 X 336) / 25" (just guessing tire size) = 2411rpm
 
69 Charger 440, bone stock. 3.23 sure grip, auto trans. 10 mpg, 11-12 if I drive 55 mph.
 
Have you checked your vacuum advance is working properly?
 
I got 18.2 MPG on my 250 mile trip to Roanoke a couple of weeks ago. That's a 440 with a 5 speed Tremec (.64 OD), 3.54 gears, and Holley Sniper FI. So I guess I'm cheating a little bit. I felt like that was pretty good though. Jetting around town to cruise ins and such I usually get around 9-10, I do have a little bit of a heavy foot problem though.
 
If you even got close to 18 MPG that is a grate deal. Yep the heavy foot dose not get good fuel Millage. LOL. Just into finding out what I am getting on my 383 runner. But just cant seem to keep my foot out of it and kick in that four barrel.
 
Jerry Hall said:
I don't have a running 318 car, but a 70 Charger is a heavy car.
Click to expand...

Heavy? That is a relative term.
When I weighed my '70 the first time, it was 3660 lbs with the stock 318-904-8 1/4" axle and 2.71 gears. Bucket seats, console, A/C and 4 wheel drum brakes.
That is not a book published number. It is a real weight measured at a certified scale. I've read from some people that spout off "My car weighs 3000 lbs, that's what it says in the book. Yeah? SURE it does....
 
Here ya go: {Quote} "That said, I'm getting enough miles on my Charger that I'm pretty confident that this is "what it gets" for MPG. 70 Charger, bone stock 318 2bbl, factory air cleaner (single snorkel), factory manifolds, dual exhaust. 904 automatic, 2.73 rear. Close-to-correct size tires - speedo reads 65, GPS on Waze shows an actual speed of 62. She's getting me a pretty consistent 13 mpg, country/mountain driving and highway driving combined. No racing - it's a cruiser, not a bracket machine - just...cruisin' around in the car I've wanted all my life."

You live in Maryland? What are the roads like there? A lot of hills and curves? I see you mentioned country/mountain driving. You're not going to get good mileage under those conditions. My teen may get 18+ on a interstate highway cruise but that is pretty flat land driving. I can get high 20's with my wife's suv around here but when we travel across the state and drive in the hills the mileage goes in the dumpster. Make sure (if you haven't already) that the engine is in a good state of tune. Double check your timing. You might benefit from a few more degrees initial, a quicker advance curve, and limit the total so it doesn't ping. You may also benefit with a rear gear change. A 3:23 will give you more pep and probably not effect your mileage much if at all. That teen under your hood won't have to work so hard when out in the hills/mountains.
 
I know the mountains won't be the best for mileage. It's the price I pay for the scenery. I asked the question not because I want to hyper-mile in a 51 year old car, but because I'm still establishing the baselines for the car. If 13 is "right" for the car...it's "right", and I'm good with that. Tune is good, timing is correct, no pinging, good power, no obvious "issues" with anything. It was purely a curiosity question. If this is the baseline, then anything better is a bonus and anything worse is a sign that I need to look for problems. That's all. I was more curious if folks thought 13 was a sign of problems with the car, or if I was good to go; not so much with "how do I make it better".
 
Points for comparison:
  1. My Dad's '71 Satellite 318-2V seldom got above 13 mpg. He might have reached 14.2 mpg on a steady highway roundtrip between Richmond and D.C.
  2. I bought the '71 Satellite from him and I can guarantee that I didn't get much above 13 mpg (when I was behaving myself) with the stock setup.
  3. I modified the '71 Satellite by adding dual exhaust, purple cam, factory 340 intake, re-curved distributor, and a Holley 4 barrel carb. I still got 13 mpg, but had more fun and I had more fun at 11 mpg. It always ran great.
  4. My '79 Chrysler 300 (stock E58 360-4V high-perf engine, stock high stall torque converter, and stock 3.2 gears) is as aerodynamic as a cinder block and weighs 4,452 lbs with 1/8th tank of gas (weight as per trucking company that moved it from Texas to Washington State). This car has always gotten 12 mpg highway or around town and runs great. I took it on a few 3,000 mile roundtrips and barely crested above 14 mpg on one tank driving in Texas (relatively flat). My worst was 8 mpg and occurred on these roads: 1) driving up and down the hilly terrain on I-81 in New York and Pennsylvania at 75 to 80 mph. 2) driving Route 58 (through Virginia) up and down the hilly and curvy roads at 55+ mph.
All is fine with your car at 13 mpg.
 
Triplegreen500 said:
OK, so yes - I am aware that "if you're worried about fuel economy, you need a new hobby". This isn't a "damn, my Charger sucks at fuel mileage!" thread - it's more a question for the group about state-of-tune.

I track the mileage (MPG) in all my vehicles as a matter of course. Not because I hyper-mile or anything like that (my size 14's are too heavy for that!)...but, like tracking my heart rate during workouts, it's a great indicator of mechanical problems and a dip in mileage for no apparent reason, makes me look at the vehicle to find out what's wrong...and fix it before any type of catastrophic failure.

That said, I'm getting enough miles on my Charger that I'm pretty confident that this is "what it gets" for MPG. 70 Charger, bone stock 318 2bbl, factory air cleaner (single snorkel), factory manifolds, dual exhaust. 904 automatic, 2.73 rear. Close-to-corret size tires - speedo reads 65, GPS on Waze shows an actual speed of 62. She's getting me a pretty consistent 13 mpg, country/mountain driving and highway driving combined. No racing - it's a cruiser, not a bracket machine - just...cruisin' around in the car I've wanted all my life.

So, for the others around - does 13 sound about right? She runs great, no flat spots, no hesitation, no stink of stupid-rich exhaust, good acceleration, no pinging, no lugging. Rolls freely, no brake drag, no bearing resistance. Or, does it sound low and I should start looking at state-of-tune stuff?

I'm not looking to turn this into a 20mpg car - that's not what this is about. Just...setting the baseline for "healthy MPG". If this is where it's happy...it is my baseline, and I go from here, no problem. But if people with a similar setup ARE getting 20mpg...I'll start digging and tuning. Healthy cars are happy cars!
Click to expand...

Yup. I have 2 fresh 318s that one is carbureted and tuned with AFR meter and O2 sensors the other is EFI. Similar gears, 2.94, in a Coronet and Duster. They get 12-13MPG on nice 65 MPH open roads and occasional freeway. The 360 I just built for the Valiant (similarly tuned) get 12MPG with 3.21 gears. The 225 Dart with dual carbs and tuned correctly gets 18 MPG with 3.23 gears. The only way to get better is lower RPM (gears, tires, overdrive), smaller cubic inches, better Volumetric Efficiency of the engine (not contrary to popular belief this is the last place to look for more milage you can only get another maybe 5%-10% max better mileage by looking at just the engine), or reducing the energy require to roll down the road (skinnier tires, 0 degrees of toe in, reducing weight, better aerodynamics). That is about it, those are the 4 main inputs to the fuel required to power an engine down the road.
 
Last edited:
JimKueneman said:
Yup. I have 2 fresh 318s that one is carbureted and tuned with AFR meter and O2 sensors the other is EFI. Similar gears, 2.94, in a Coronet and Duster. They get 12-13MPG on nice 65 MPH open roads and occasional freeway. The 360 I just built for the Valiant (similarly tuned) get 12MPG with 3.21 gears. The 225 Dart with dual carbs and tuned correctly gets 18 MPG with 3.23 gears. The only way to get better is lower RPM (gears, tires, overdrive), smaller cubic inches, better Volumetric Efficiency of the engine (not contrary to popular belief this is the last place to look for more milage you can only get another maybe 5%-10% max better mileage by looking at just the engine), or reducing the energy require to roll down the road (skinnier tires, 0 degrees of toe in, reducing weight, better aerodynamics). That is about it, those are the 4 main inputs to the fuel required to power an engine down the road.
Click to expand...


The 5.7 equipped Cuda I have gets 20.2 on the highway.
 
My former 69 1/2 Superbee 440 Sixpack 4 speed with 4.88 gears would use an 1/8 of a tank of gas everytime the outboard carbs were opened up!
 
Fuel economy with a Charger? :rofl: Would watch the gauge go down while going down the road in my 440/auto R/T. That being said, the 69 Satellite I primarily drove to school, 318/auto/single exhaust/2.76 gears did 16-17 around down/short trips.
 
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