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Re: slant 6, fuel mileage. what should i get?
[Re: DaytonaTurbo]
#54897
03/15/08 03:41 PM
03/15/08 03:41 PM
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Joined: Mar 2006
Posts: 1,611
Pataskala, Ohio
GTX70sixpack
top fuel
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top fuel
Joined: Mar 2006
Posts: 1,611
Pataskala, Ohio
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I had a 67 Dart GT vert and a Spirit of 76 Dart that I drove for several years back in the 80's. They both got 16mpg. I had a 318 Charger and a 318 Coronet, the Charger got 18mpg and the Coronet 21mpg. My son,s 66 Dart SW when it had a 318 got 22mpg. These are all highway miles. In perspective if I drive my GTX nice, it gets 16.5 with the 440-6. Although normally I'm at 14 on it. My V6 Dakota gets 20mpg and my polyspere 318 65 9 pass wagon gets 19.
65 Belvedere II Station Wagon
69 Coronet R/T convertible
70 GTX
70'cuda
99 Dodge Diesel dually 4X4
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Re: slant 6, fuel mileage. what should i get?
[Re: DaytonaTurbo]
#54898
03/15/08 03:41 PM
03/15/08 03:41 PM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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Hmm, are those Imperial gallons he's getting 21 mpg with that Diplomat? Cause if so then it works out to about 16 mpg using US gallons.
I had a 72 Swinger with a 225, 2.45 gears, and it was lucky to pull 10 mpg on it in mixed driving. But I attribute that to the 2.45 gears. Swapped in an 8 1/4 to replace the 7 1/4 and never thought to see what gears it had. That was a big mistake.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: slant 6, fuel mileage. what should i get?
[Re: dirt]
#54899
03/15/08 03:50 PM
03/15/08 03:50 PM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
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Depends on much more than the cubic inches or cyls. I have a 68 cuda with a 318 that gets 29 highway and 19 city. The slant could do better if properly built and set up similarly. Why would anyone drive a slant car if you were only getting 16mpg 
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: slant 6, fuel mileage. what should i get?
[Re: dirt]
#54900
03/15/08 04:39 PM
03/15/08 04:39 PM
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Joined: Jan 2003
Posts: 2,511
Tampa , Fl
MoparJoe
super gas
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super gas
Joined: Jan 2003
Posts: 2,511
Tampa , Fl
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I was getting 15mpg out of my Duster when it had a 225 /6 1 barrel/904/2.76 7 1/4, most of my driving was hwy 65-70mph.
It was all stock and was in good shape, motor was in tune and had a carter 1 barrel- It was my driver for about 2 years like that.
When I swapped in a mild 318/998 I was getting 20-21mpg with the same rear & driving conditions.
The 318 had about 9.3 comp, 268 comp cam, 360 heads, M1, 600 eddy carb, headers & 2 1/2" duals w/turbo muffs.
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Re: slant 6, fuel mileage. what should i get?
[Re: dirt]
#54903
03/15/08 06:40 PM
03/15/08 06:40 PM
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Joined: Nov 2006
Posts: 203
Taneytown, MD
bigslant6fan
enthusiast
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enthusiast
Joined: Nov 2006
Posts: 203
Taneytown, MD
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I,m getting 24 MPG in a 3,400 lb S/6 a-body with a 470 lift cam,3.23 gears,and a turbo. If your not getting at least 25 MPG out of a S/6 a-body car,something is bigtime wrong.Check for missconected dist. advance line,blown advance cannister(very common with S/6 engines leaking oil on pass side of engine),flooding carb,stuck advance weights.I bought a S/6 79 volare and discovered the advance weights were stuck.I ran into the prevous owner 6 month latter and he said he sold the car because of a lack of power,and poor fuel economy.He s#@t a brick when I told him I was getting 23MPG. Also, the first thing I,d check is those gears,you say its "screeming along at high way speeds"2.76 or 2.94 are what most cars came with. 
Last edited by bigslant6fan; 03/16/08 09:34 AM.
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Re: slant 6, fuel mileage. what should i get?
[Re: dirt]
#54904
03/15/08 07:59 PM
03/15/08 07:59 PM
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Joined: Aug 2007
Posts: 469
New York, USA
fluegelmeister
mopar
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mopar
Joined: Aug 2007
Posts: 469
New York, USA
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Quote:
I have a slant 6 dart automatic and its only getting around 16 mpg , mostly interstate driving some on the back roads. is this average? would a 4 speed overdirve help verymuch? it is winding pretty tight on the interstate but i am not sure of what the gears are in it. and i dont have a tach in it either but it screams right along.
just looking to get some better mileage. i got 16 mpg with my 318 cuda!
Try tuning it up:
1. Adjust the valves
2. Adjust points or better yet, replace points with transistorized ignition
3. Check timing
4. new plugs & wires
5. Check heat valve isn't stuck
6. If equipped, check the EGR
7. rebuild the carb and adjust the floats to spec. Tank the cast parts if possible.
8. Check PCV
I think it should get 19-21. That's what I used to get with my valiant.
Good luck,
Barry
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Re: slant 6, fuel mileage. what should i get?
[Re: fluegelmeister]
#54905
03/15/08 10:55 PM
03/15/08 10:55 PM
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Joined: Jan 2003
Posts: 9,887
USA
CrAlt
master
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master
Joined: Jan 2003
Posts: 9,887
USA
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My 225/904/2.76's 4dr abody gets about 20-22mpg. It runs like crap because ive never tuned it and i think has a small vacuum leak or a dead cyl at idle.
I was asked to contribute money to help solve the civil unrest in Egypt, but I suspect it's some sort of pyramid scheme.
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Re: slant 6, fuel mileage. what should i get?
[Re: CrAlt]
#54906
03/16/08 01:26 AM
03/16/08 01:26 AM
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Joined: Jan 2003
Posts: 8,089
Sorrento, BC, Canada
4speeds4me
master
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master
Joined: Jan 2003
Posts: 8,089
Sorrento, BC, Canada
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Dad had a 74 \6 Duster and I had a 70 \6 duster, as well as a 65 \6 Valiant, but the Valiant was a 3 speed manual. Got 29 with the Valiant at 17 years old. Got 28 with the 70 and dad consistently got 30 with his 74. That's to an Imperial gallon. That would convert to 23-25 for a US gallon.
2 Demons...no, not my kids! 
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Re: slant 6, fuel mileage. what should i get?
[Re: dirt]
#54907
03/16/08 09:07 AM
03/16/08 09:07 AM
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Joined: Feb 2003
Posts: 8,020
Pangaea
B5 Bee
master
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master
Joined: Feb 2003
Posts: 8,020
Pangaea
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My '84 D100 gets 20mpg at 65mph. 225, 833od, 3.91sg, 235x15 tire
My '68 V200 gets 25mpg at 65mph. 225, 904, 2.94peg, 185x13 tire
My sister bought a loaded '80 Mirada new, even had the am/fm/cb/cassette radio, 225, 904, 2.45, 215x14 tire, it got 23mpg at 70mph.
There's something wrong with a slant six A body that gets less than 20mpg/hwy.
Last edited by V code '70 Bee; 03/16/08 09:09 AM.
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Re: slant 6, fuel mileage. what should i get?
[Re: slantzilla]
#54909
03/16/08 10:50 AM
03/16/08 10:50 AM
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Joined: Jan 2008
Posts: 3,886
Lost and Spaced
bboogieart
master
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master
Joined: Jan 2008
Posts: 3,886
Lost and Spaced
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do you have a stick or auto' either way there are overdrive options for both, the stick would be easier. also rear gears and tire size will make a world of difference. I have had many leaning towers and they were very tough, but not necessarily mileage conscious. How ever they are easily modified for both mileage and power.It really depends on the whole combo. Start with the tallest tire you can fit. Look for tall rears gears, should be able get a complete rear cheap to slip under it. do you know how to check your gears? Remember any of these changes will affect your speedometer.
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Re: slant 6, fuel mileage. what should i get?
[Re: dirt]
#54913
03/17/08 08:25 AM
03/17/08 08:25 AM
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Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
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my duster gets about 25mpg combined with a all stock slant6 1bbl, A833OD, and a 3.21 rear with 25" tall tires. beating on it in town I've never gotten worse than 18-19. best highway mileage I've gotten was 32mpg sticking to a constant 60mph.
that's in an all stock '76 A body, I'm guessing the car is 3200-3300 lbs.
1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: slant 6, fuel mileage. what should i get?
[Re: FarDarter]
#54914
03/17/08 03:53 PM
03/17/08 03:53 PM
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Joined: Oct 2003
Posts: 411
Texas
vynn3
mopar
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mopar
Joined: Oct 2003
Posts: 411
Texas
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Quote:
Slant sixes don't get good enough mileage to justify their existence. I did a five tank log on my Dart and the best was 21.29 while the worst was 17.40. The average was 19.13. In my opinion, that isn't good enough to live with the total lack of power.
I had an '84 Celica GT-S that got about 29 on a cross country trip at about 75 mph with the AC on full blast and it was faster than my Dart, too. I've gotta have either better mileage or more power than the Toyota with my Mopar. That's why I'm putting a 318 in it. With a small cam and an A-500, I'm betting it will do better than the /6.
And what condition is your slant in? How many miles? Sure, a new or freshened 318 can get better mileage than a tired old slant, but the same overdrive and a rebuilt slant with a few cheap, basic mods like a Super Six 2bbl and good exhaust will get mileage in the 20-25 mpg range.
If the car is a weekend toy, then sure, why not drop in a V-8. Heck, why stop there? Go big block.
But if you're using a car for a daily driver, with gas prices rising AGAIN, then 2-4 mpg makes a big difference to MY wallet.
I realize this is a hot rodder forum, but I don't like my job well enough to need more than 200hp to get there. I drive my toys on the weekend.
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If you've got the time, this is a VERY informative read.He's done his homework, and has got the numbers to back it up! 
