Gas mileage 225 Slant 6

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Analogprincess

Analogprincess

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Monterey, CA
I’ve just acquired my ‘66 Dart and my gas gauge doesn’t work.

It has a 225 slant 6 and I was wondering what kind of gas mileage I should expect to be getting driving around town.

852C6EB1-8D96-463E-A208-99DC52DD0ECD.jpeg
 
Hard to tell around town. Fill it up and watch the odometer. go about 50 miles and fill to see how much you used.
 
It should get 17 -20 depending on how you drive it and how much ethanol there is in the fuel.The more ethanol the lower your gas mileage will be.
 
Wow that puts my 15.6 highway to shame in my 273 V8
 
Most of my driving has been around town lately and when I do hit the freeway it's almost all accelerating (I have a 14 mile commute, split between four different highways and 4 miles of surface streets)

I am averaging a hair over 20mpg, verified against GPS, always using the same gas station. Generic 87 octane with 10% ethanol. 225/904/7.25"/13's
 
BKCowGod said:
Most of my driving has been around town lately and when I do hit the freeway it's almost all accelerating (I have a 14 mile commute, split between four different highways and 4 miles of surface streets)

I am averaging a hair over 20mpg, verified against GPS, always using the same gas station. Generic 87 octane with 10% ethanol. 225/904/7.25"/13's
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That sounds about right.
 
With the 170 cu in slant I have in my 65 Valiant wagon I get 23-25 on the highway.I have a 1965 A833 ball & trunion type 4speed and 7 1/4 323 sure grip with 13 inch tires .It's fun to drive and doesn't break the bank
 
I daily drove a stock 1 bbl slant six for years in a 67 Dart GT, 225, 904 and 7 1/4 with 2.93 open gears. Mixed driving in So Cal traffic and my average was 17 mpg. Then I cut .100 off the head with some work and bigger valves, long tube headers and Holley 1920 rejetted and got 20 mpg.
 
1st up, welcome to FABO @Analogprincess. 2nd, You can see the ballpark You're in above, pretty much typical. 3rd, don't listen to advice from anyone telling You to run "Plus-Silver-etc.", or worse "Gold-Ultimate-etc.". Any more octane than You need makes less power, wastes heat energy into the coolant/exhaust systems, both of which hurts mpgs. I'm not sure what the avg. alcohol content is in Your area, but as noted above, more can hurt....and 87 octane is plenty.
 
Killer6 said:
1st up, welcome to FABO @Analogprincess. 2nd, You can see the ballpark You're in above, pretty much typical. 3rd, don't listen to advice from anyone telling You to run "Plus-Silver-etc.", or worse "Gold-Ultimate-etc.". Any more octane than You need makes less power, wastes heat energy into the coolant/exhaust systems, both of which hurts mpgs. I'm not sure what the avg. alcohol content is in Your area, but as noted above, more can hurt....and 87 octane is plenty.
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Thanks!
 
Analogprincess said:
I wish I could do that but none of my instruments work.
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The speedometer/odometer is mechanically driven by a cable from the transmission, independent entirely from an electrical issue with the other gauges.
 
Killer6 said:
1st up, welcome to FABO @Analogprincess. 2nd, You can see the ballpark You're in above, pretty much typical. 3rd, don't listen to advice from anyone telling You to run "Plus-Silver-etc.", or worse "Gold-Ultimate-etc.". Any more octane than You need makes less power, wastes heat energy into the coolant/exhaust systems, both of which hurts mpgs. I'm not sure what the avg. alcohol content is in Your area, but as noted above, more can hurt....and 87 octane is plenty.
Click to expand...
Damned if I never considered this. I'm 14 years retired from a Colorado state vehicle emissions testing laboratory. This was not a state inspection site but rather research lab. I was licensed to perform and issue valid inspection certificates, however this was done only when lab testing problem vehicles. Anyhow, I suspect that since the high octane fuels are supposed to burn slightly slower, perhaps more heat could be sent into the cylinder walls. Makes sense to me. The level of heat tranfer may be somewhat small, but that issue was never tested in our lab during my time there. Still, makes sense.
Jerry
 
If I had to guess, I'd say you'll average about 18mpg.

Usually you have to do some mods to get consistent 20-21mpg.
 
I consistently get 16 mpg with my slant in a 68 dodge dart 2 door H/T with a 1976 OD 833.

I am kinda a lead foot and with a slant you have to be a lead foot to push it to keep up with today's traffic.

Don't expect much from a slant, sure it's only a six cylinder but it's also a heavy and very old engine that was designed to run at 55 mph or less, more so on the less part.
 
BKCowGod said:
Most of my driving has been around town lately and when I do hit the freeway it's almost all accelerating (I have a 14 mile commute, split between four different highways and 4 miles of surface streets)

I am averaging a hair over 20mpg, verified against GPS, always using the same gas station. Generic 87 octane with 10% ethanol. 225/904/7.25"/13's
Click to expand...
Sounds like hell. Reminds me of Seattle
 
At the minimum You should be getting the low 20's in the highway for mpg no matter what it is
My coronet deluxe 4 dr 225/3 on the tree got 22 - 24 on the highway at 70 mph. 2.94 8-1/4. Volare super six with a/c was 17-24.

The mechanical rolling resistance needs to be at a minimum. Slant sixes are notorious for stretched timing chains. There must be no stretch in the chain or they run for %$#@.
Min operating temp 195
Tune up
Exhaust
Tire/wheel size choices
Lubricants - very key to the rolling resistance or lack there of
Suspension
Gearing
A bit of aerodynamics - you would be surprised....
 
If I've noticed one thing in all my years of driving, owning cars and trucks, and working on them for a living/
Most vehicles I have owned I have had "2 of" or more.
When I had my 1st XJ Cherokee, I had very little trouble with, very consistent and predictable 16/20 mpg, just a great vehicle.
After my son spun it 180* on a slick road and rolled it into a ditch during his 1st winter as a driver we replaced it with another, seemingly identical except for the color.
This 2nd one gave me electrical fits that the 1st one never did, lots of issues the 1st one never gave
And not as good on gas either.
Same story on the 2, ex police diplomats, the 85 was great, so much so we then has an 89, which was a pile of junk. And lather rinse repeat with the several other vehicles I've had over the years.

I see a wide variety of results for the same questions on different /6 vehicles here.... hardly 2 of the same stories among them... Could be "built on Monday" (or not), advance in distributor not working the same between them, different gearing, different driver routes, different clearances within the engine, dragging brakes on some and not on others, different gas quality, who knows?
 
volaredon said:
If I've noticed one thing in all my years of driving, owning cars and trucks, and working on them for a living/
Most vehicles I have owned I have had "2 of" or more.
When I had my 1st XJ Cherokee, I had very little trouble with, very consistent and predictable 16/20 mpg, just a great vehicle.
After my son spun it 180* on a slick road and rolled it into a ditch during his 1st winter as a driver we replaced it with another, seemingly identical except for the color.
This 2nd one gave me electrical fits that the 1st one never did, lots of issues the 1st one never gave
And not as good on gas either.
Same story on the 2, ex police diplomats, the 85 was great, so much so we then has an 89, which was a pile of junk. And lather rinse repeat with the several other vehicles I've had over the years.

I see a wide variety of results for the same questions on different /6 vehicles here.... hardly 2 of the same stories among them... Could be "built on Monday" (or not), advance in distributor not working the same between them, different gearing, different driver routes, different clearances within the engine, dragging brakes on some and not on others, different gas quality, who knows?
Click to expand...
The sad reality is, most of us don’t have the time or money to make a 50-year-old vehicle run like new. I’m sure that’s got a lot to do with the difference in economy people see with these motors.
 
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