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What can you reasonably expect for fuel economy?

moparedtn

moparedtn

I got your Staff Member riiiight heeeere...
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Obviously, fuel economy isn't any of our cars' strong suits - not what they were
built for, after all.
That said, I actually paid a little bit of attention on today's 100-mile round trip
to the Cruise Against Cancer event in Newport, TN - and the results didn't exactly
surprise or disappoint me?

Reminder - Fred is a '68 GTX with a mild 440 w/purpleshaft, headers, 3" dual (LOUD)
exhaust, 4 speed, 3.55 gears.

What should I have expected for highway cruising on ethanol-free 93?
 
I think 9-11 also, 12 or 13 I would be happy with. Highway speed out here is at least 65, 70 is normal and nobody gets a ticket for that. A little further out of town it's 75 and nobody gets a ticket doing 80. At that speed I'd be getting maybe 8 and have a headache from the roar of the engine.
 
Tennessee is hilly?:rolleyes:

9.2 mpg
 
I'm running 3.73's, 26.5" diameter tires. Gearvendor O/D on 727 automatic in a '67 4dr Coronet. Stroked 496. Fuel injection set at 14.7 AFR. I get 10mpg at 80 on the interstate.
 
DeltaV said:
When are you going to tell us what you averaged on that 100 mile trip?
Click to expand...
Dang man, I was gonna wait to get a bit of a cross-section of folks to get an average worked up.
Sheesh. :)
Okay, to give more information on the trip...
- Tires on rear are 28" tall (275/60/15)
- speed was a pretty darn constant 63-4mph (Fred's "sweet spot")
- terrain was equal parts hilly and flat (pretty much equal elevation between points, though - around 1200'
ASL)
- temperature was 60's on the way down, 80's on the way back
- Fred ran pretty cool the whole way but REALLY cool on the way down this morning

The wild card in all this is the "reman" Edelbrock 750 that came with the engine when I got it;
I've been through it and got the as-supplied jetting and rods in it and the car runs decent with it,
but there's the usual throttle slop in it.
(Yes, it's on the "replace" list one day...)

Ok - near as I can figure, Fred went through about 8.5 gallons to go 100 miles (11.76mpg).
Not quite bad enough to be able to watch the gauge drop in real time - but noticeable. :)
 
I would be happy with that. Sounds like your car is running right. Enjoy.
 
71RRHI said:
I would be happy with that. Sounds like your car is running right. Enjoy.
Click to expand...
Thanks.
I really don't have any recent memories to compare it to (haven't driven long distances with a old
440 in many years now), but in the old days of cruising up and down the northeast to shows and events,
seems like I remember slightly better (but still comparable) results with a b-body with 3.91's...
 
I paid $6.69 yesterday for 91 with up to 10% ethanol.
Not to try to top you, Ed. Southern CA is the pinnacle of fuel price here.
On Thursday, I got 13.4 with similar gearing and tire height but doing fairly steady 70-80 mph on flat ground. I do have the .64 fifth gear though.
I agree, these are in no way “economy “ cars but it still makes sense to optimize efficiency where you can. I could probably crack 15 if I drive a steady 65 and didn’t try to pass anyone.
 
Last edited:
moparedtn said:
Ok - near as I can figure, Fred went through about 8.5 gallons to go 100 miles (11.76mpg).
Not quite bad enough to be able to watch the gauge drop in real time - but noticeable. :)
Click to expand...

I think that's good/what I would expect.

My 59 Cadillac with a 390 and 3.36 gear gets 13.

My 69 Charger on E85, EFI, .82 overdrive and 4.10's (5th pretty close to 4th gear with 3.55's) is 9.
 
Kern Dog said:
I paid $6.69 yesterday for 91 with up to 10% ethanol.
Not to try to top you, Ed. Southern CA is the pinnacle of fuel price here.
On Thursday, I got 13.4 with similar gearing and tire height but doing fairly steady 70-80 mph on flat ground.
I agree, these are in no way “economy “ cars but it still makes sense to optimize efficiency where you can. I could probably crack 15 if I drive a steady 65 and didn’t try to pass anyone.
Click to expand...
If I recall, your gearing situation is much better by comparison, no?
 
Sorry, I edited the post to include the overdrive fifth gear.
Final drive in OD is 2.27 to 1.
 
Photon440 said:
I think you can expect fuel consumption, but not fuel economy.
Click to expand...



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Fuel mileage is something that will affect me a a lot on my trip across country.

In my 2015 trip my 383 based (stock engine with a FAST fuel injection system) 70 Road Runner, with a .73 overdrive averaged 17.2 MPG for the whole trip. That included half the trip when we pissed fuel out the vent after filling the tank (the vent was not set up properly).

For my trip starting next week, I will be driving my 73 Road Runner with a 340 based stroker with 416 cubic inches, a 727 with a Gear Vendor's overdrive (.78 OD). I am running a Thermoquad carburetor from a 400. We will see what I get; I will be happy with 15 if I can get it. With high gas prices and an estimated 10-11,000 miles for the trip, fuel is going to be expensive, so every MPG counts!
 
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