slant 6, fuel mileage. what should i get?

Posted By: bigslant6fan

Re: slant 6, fuel mileage. what should i get? - 03/15/08 10:40 PM

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.

Posted By: fluegelmeister

Re: slant 6, fuel mileage. what should i get? - 03/15/08 11:59 PM

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

Posted By: CrAlt

Re: slant 6, fuel mileage. what should i get? - 03/16/08 02:55 AM

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.

Posted By: 4speeds4me

Re: slant 6, fuel mileage. what should i get? - 03/16/08 05:26 AM

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.

Posted By: B5 Bee

Re: slant 6, fuel mileage. what should i get? - 03/16/08 01:07 PM

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.

Posted By: slantzilla

Re: slant 6, fuel mileage. what should i get? - 03/16/08 02:16 PM

I have had a 1bbl Slant get as much as 24 in my '66 Valiant. My first good motor got 22 with a 390 Holley on it. Jetting and timing are crucial to mileage on a Slant.

Posted By: bboogieart

Re: slant 6, fuel mileage. what should i get? - 03/16/08 02:50 PM

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.

Posted By: mopowergtx

Re: slant 6, fuel mileage. what should i get? - 03/16/08 11:26 PM

Had a well tuned 80 Aspen 2dr with the stock Holley 1 Barrel and 33,000 orignal miles and best was 18mpg daily commuting to work. Same engine, pulled it and dropped it in my 79 Aspen in my sig pic and installed it with that cars orignal Super Six intake/carb setup with no other changes. Same daily commute and it gets 22 mpg consistently. Oh they both had 2.76 geared 7 1/4" rear ends with automatics. The best I ever got out of it was a 2 and half hour trip one way to Norwalk C.C. last fall and it got 25 mpg.

Posted By: FarDarter

Re: slant 6, fuel mileage. what should i get? - 03/17/08 12:29 AM

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.

Posted By: dirt

Re: slant 6, fuel mileage. what should i get? - 03/17/08 01:24 AM

i am thinking of a v8 swap in place of the /6 in the dart. i figure if its going to suck gas it may as well have the power. i have a 71 360 with 72,000 original miles on it that i may put in. it still is a good running motor and with a overdrive 4 speed it may not be too bad on gas.

Posted By: patrick

Re: slant 6, fuel mileage. what should i get? - 03/17/08 12:25 PM

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.

Posted By: vynn3

Re: slant 6, fuel mileage. what should i get? - 03/17/08 07:53 PM

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.

Posted By: FarDarter

Re: slant 6, fuel mileage. what should i get? - 03/17/08 10:53 PM

Good luck getting 200 hp out of a slant six!

Yeah, you can do it but the mileage will probably go out the window at that point. Then you'll have bad mileage and only 200 hp!

Posted By: 4speeds4me

Re: slant 6, fuel mileage. what should i get? - 03/18/08 12:53 AM

Geez...early 70's 225 single barrels were 145bhp. Headers and some creative cam and headwork, and 200 really isn't out of line. Let alone looking at a fairly easy turbo swap which should offer considerably more. Let's not even mention that Hyper-pak engines were already pretty much there, at 195.

I don't know why everyone's always dumping on the slant. It's a decent (or should be) economy engine with a LONGSTANDING history for longevity that is hard pressed to be matched by ANY production passenger vehicle engine.

Posted By: FarDarter

Re: slant 6, fuel mileage. what should i get? - 03/18/08 01:24 AM

It's not a bad engine. It is quiet and very smooth and it does get the car from place to place just fine. It's just not fun. Not at all.

I think most of us here are the kind of guys who can enjoy just standing behind our cars and listening to the rumble of the dual exhaust. To watch the car sink a little bit on the right when we stab the gas in neutral. To feel the vibrations of the engine through the whole car. It's more than the numbers that we get out of a nice V-8. Old American cars are just meant to have them!

Posted By: 4speeds4me

Re: slant 6, fuel mileage. what should i get? - 03/18/08 02:20 AM

Now THAT I agree with, but after making the ugly payments on a new car, and dealing with dealerships and shops for everything because the things are too freaking cramped (or under warranty) to work on, I gotta say...a late 60's-mid 70's A-body with a slant (or 318, as hotroddave40 has proven) that'll knock down better mileage than my current daily drivers, (or past, considering the last 5 years) gets awfully appealing when there's not a thing that requires me to seek outside service, and NO PAYMENT!

Posted By: mr.318

Re: slant 6, fuel mileage. what should i get? - 03/18/08 02:53 AM

I had one in a 79 dipomat supersix 2barr. that got 26 on the highway,And i don't know what they get m.p.g. But i've seen the slant six class raceing twice and some of those cars are running over 120mph in the 1/4,Thats faster than a toyota and more fun, but then i don't know cause i'd never drive one

Posted By: slantzilla

Re: slant 6, fuel mileage. what should i get? - 03/18/08 12:49 PM

Quote:

Good luck getting 200 hp out of a slant six!

Yeah, you can do it but the mileage will probably go out the window at that point. Then you'll have bad mileage and only 200 hp!

Mine is around 240 on motor and 375 on the hose. It still got almost 20 on the highway with 3.91 gears and a 3500 stall converter.

Posted By: dirt

Re: slant 6, fuel mileage. what should i get? - 03/18/08 01:01 PM

some one mentioned a turbo. i used to run a shelby Z daytona with turbo it got 31 MPG on the interstate and was fun to drive....until i wraped it around a tree when i was 19. but i still have the car and thought it would be cool to put the turbo or another turbo on my slant 6 dart.
I know the /6 is strong and at least when its stock its indestructible! how complicated would it be to put a turbo on one? i know how it works and i know i could fabricate everything to hook it up but what about over boosting or selecting the right turbo? I would like to keep it cheap , like junk yard stuff. would you just plumb in the turbo from a daytona and see what happens? would the compression in a /6 be low enough to work? how many punnds boost would be safe with a stocker?

i am just thinking out loud here, thanks for any advice, the blue one
is my $400 beater /6 the other one is my 70 340 that i restored 15 years ago.

Posted By: vynn3

Re: slant 6, fuel mileage. what should i get? - 03/18/08 01:05 PM

Quote:

I think most of us here are the kind of guys who can enjoy just standing behind our cars and listening to the rumble of the dual exhaust. To watch the car sink a little bit on the right when we stab the gas in neutral. To feel the vibrations of the engine through the whole car.

My mildly-modified slant has true duals (and a nice rumble), the torque rotates the engine nicely in neutral, and makes plenty of nice vibrations through the car. On top of that, it makes a roar on the highway akin to a WWII fighter plane, rather than the V-8 noises that come from every Tom, Dick and Harry's Camaro, Mustang, or pick-up.

Sure, apples to apples, with the same mods a V-8 will always make more power. But my slant responds well to modifications (sometimes better than a V-8 � the 2bbl and Dutra Dual exhaust made a night and day difference in power, and got BETTER mileage!), it's easy to work on, and gets a different kind of interest when I pop the hood. Finding slant parts is more challenging than finding V-8 parts, but the same applies to finding Mopar small block parts compared to Chebbie parts. For example, my "long rod" slant has longer 198 rods and 2.2 4-banger pistons, giving it the same displacement but a better rod ratio and lighter pistons. Slanters like Doug Dutra have to get "creative" to make up for the lack of hot parts. I LIKE that challenge. But, to each his own.

I'm not knocking V-8's, I've owned plenty over the years, and I have a wonderful little V-8 Dart GT now. I love 'em for what they are and what they can do. But my slant is UNIQUE, and uniqueness is what lured me to Mopars and away from Fords and Chebbies in the first place.

I happen to think there's room enough for hot slants, small blocks, AND big blocks in the Mopar world (not to mention V-6's and inline 4's) without knocking the other engines. They can ALL be fun and cool in their own way.

(But yes, Dave, there's not an engine out there that will get me HOME from work fast enough.

)

vm

Posted By: finadk

Re: slant 6, fuel mileage. what should i get? - 03/18/08 01:46 PM

Up until a few months ago felt that a /6 was only good as a boat anchor. Once gas hit $3 a gallon I started to research the slanty six a bit and elected to go with an 80 Volare /6 over a 318 Duster for my Son's first car. Sure a 318 can get good milage with careful driving but the /6 has does respond well to traditional hot rod upgrades and is as reliable an ax. Checl our slantsix.org for all you will ever need to know.
The "Super Six" 2 barrels get better milage than the one barrel. My car is not on the road yet so I cant speak to gas milage but I have had many 318's and never saw more than 12 mpg with any of them, not that it cant be done but I live in the north east and there is just a lot of stop and go, even on the highways.
the car we found was an automatic but with a stick even a 90hp 1bbl would be fun to drive.

Posted By: 4speeds4me

Re: slant 6, fuel mileage. what should i get? - 03/18/08 06:44 PM

Quote:

some one mentioned a turbo. i used to run a shelby Z daytona with turbo it got 31 MPG on the interstate and was fun to drive....until i wraped it around a tree when i was 19. but i still have the car and thought it would be cool to put the turbo or another turbo on my slant 6 dart.
I know the /6 is strong and at least when its stock its indestructible! how complicated would it be to put a turbo on one? i know how it works and i know i could fabricate everything to hook it up but what about over boosting or selecting the right turbo? I would like to keep it cheap , like junk yard stuff. would you just plumb in the turbo from a daytona and see what happens? would the compression in a /6 be low enough to work? how many punnds boost would be safe with a stocker?

i am just thinking out loud here, thanks for any advice, the blue one
is my $400 beater /6 the other one is my 70 340 that i restored 15 years ago.

Turbo from a 3.8L GM is perfect for this, as displacement is almost identical... Turbo Regal, etc...and I happen to have one...

Posted By: groovy ghoulie

Re: slant 6, fuel mileage. what should i get? - 03/18/08 08:19 PM

Back in the early 1990s I knew a soldier on Fort Sill who had a 225 slant six in a two door post seafoam green 1964 Dart.

He had tricked the thing out with a custom built header, a magneto, an Offy four barrel intake and a bumpy cam with a stock push button tranny behind it all.

I swear that thing would only lope about once every ten seconds at an idle but that thing would freakin' scream when he shot the coals to it.

I've often wondered if it's still alive somewhere....?

Posted By: Anonymous

Re: slant 6, fuel mileage. what should i get? - 03/30/09 11:00 PM

I own a 72 dart swinger with a 225 slant 6 in it. and my fuel mileage is anywhere from 7 yes 7 to 13 mpg. The thing is driving me a little nuts since it is my daily driver. I bought and installed new spark plugs, spark plug wires, it has the stock electrical ignition, an accel coil. the gears are 2.79 if I remember right and is an 3 speed automatic. the car only has about 160,000 miles on it too and from what I hear and read that is about the half way point on these cars. I also had the timing redo by a mechanic and he set it to 5 twice the amount of what the stock is of 2.5 so I am not too sure if that helps any. I am still new to the car world and am learning a lot on the way to fixing my dart up.

When I bought it the previous owner already installed a two barrel carburetor, I am not too sure of which it is I will have to check and post later.

But I am seriously hoping I can do much better than 13 mpg so if you guys can give me any further detail it would be much appreciated.

Posted By: dgc333

Re: slant 6, fuel mileage. what should i get? - 03/30/09 11:11 PM

My 68 Barracuda with an A833OD tranny and 3.55 gears with this engine would get 19-20 mpg around town and 22-23 mpg on the hiway. I figured this engine was making around 180-190 HP

Now with this 360 ,which makes ~370HP, in the same car with same tranny and gears will get 17-18 mpg around town and 21-22 mpg on the hiway.

Posted By: mark7171

Re: slant 6, fuel mileage. what should i get? - 03/30/09 11:51 PM

my 323" (.430/.444" cam) 4 spd, and 3.23 gears < It gets 14-15mpg. Well tuned.

my 4der, will accelerate fast, like a 90's 5.0L mustang 5 speed. At least the first 4 gears, with no OD833. No 13 seconds. No 20+ MPG.

Posted By: patrick

Re: slant 6, fuel mileage. what should i get? - 03/31/09 12:58 AM

my bone stock '76 with a 225 1bbl, A833OD, 3.21 gears and 25" tall tires knocks down 19-22mpg city, 25-28mpg highway with a best of 32. a lot of people actually report marginally BETTER mileage after retrofitting the super 6 2bbl setup...

your combo I'd expect about 18-20 city and 22-24 highway.

I'd look at maybe a carb rebuild.

Posted By: elmor

Re: slant 6, fuel mileage. what should i get? - 03/31/09 02:35 AM

There is a local guy that runs a 225 in 65 Valiant wagon. He's running with the big blocks at the local strip. Knocks down mid to low 12's consistently. They will run hard with some TLC!

Posted By: Anonymous

Re: slant 6, fuel mileage. what should i get? - 03/31/09 02:44 AM

Quote:

my bone stock '76 with a 225 1bbl, A833OD, 3.21 gears and 25" tall tires knocks down 19-22mpg city, 25-28mpg highway with a best of 32. a lot of people actually report marginally BETTER mileage after retrofitting the super 6 2bbl setup...

your combo I'd expect about 18-20 city and 22-24 highway.

I'd look at maybe a carb rebuild.

So I found out what my fuel problem was as I went to go look at what type of carburetor I have. And the verdict was having a huge wad of a paper towel shoved in my air blower.... my carburetor was sucking for air and couldn't get any... I can already tell the difference of how much less I have to push the pedal to go at freeway speeds.

And answering someone who asked about how much boost a slant 6 can take. from all the research I have done, since it has an 8:4:1 compression ratio it has been able to take 24-26 pounds of boost max which is a hell of a lot. I don't know if some one's engine survived after that but that is what I read if you are planning on turboing your slant 6.

Posted By: 500ciDuster

Re: slant 6, fuel mileage. what should i get? - 03/31/09 02:58 AM

I have a 225 in a 74 Duster automatic with 2.7 gears and it gets 20-25 which is about the same as my 94 Chysler New Yorker with the 3.5.

Mitch

Posted By: dulcich

Re: slant 6, fuel mileage. what should i get? - 03/31/09 03:33 AM

Stock slant gets about 18 mpg average if everything is right. Very inefficient motor.
-dulcich

Posted By: mark7171

Re: slant 6, fuel mileage. what should i get? - 03/31/09 03:59 AM

Quote:

There is a local guy that runs a 225 in 65 Valiant wagon. He's running with the big blocks at the local strip. Knocks down mid to low 12's consistently. They will run hard with some TLC!

that is almost impossible.

9+ to 1 compression I6. 4.88 gear. mechanical cam MP4286681. race everything. Abody stripped to less than 2750 lbs. 4 speed. no rear brake contact. no front bearing drag. suspension set for drag only.

You get....high 14's

....and no mileage worth typing. Save your money.

Posted By: Dallasdart

Re: slant 6, fuel mileage. what should i get? - 03/31/09 05:27 AM

it's been a while since I have been in the slant forum but I know there are several A body guys running 12's. It's possible, just very $$. I had a 66 dart with a slant and a 3 on the tree. Loved that car and after I rebuilt the tired motor it was a strong car.

Posted By: volaredon

Re: slant 6, fuel mileage. what should i get? - 03/31/09 01:21 PM

Quote:

Stock slant gets about 18 mpg average if everything is right. Very inefficient motor.
-dulcich

go tell the rest of the guys how "inefficient" the /6 is over on the /6.org board and be ready for a flame war! I've had efficient ones and inefficient ones just like I have with V8s. My Dad had an 82 Gran Fury in which I had PLENTY of seat time in that got 28 MPG over the road (NO I am NOT dreaming) /6. Ive seen lotsa "modern" V-6s with all their computer BS and injection that can't do that!!!

Posted By: Magnum

Re: slant 6, fuel mileage. what should i get? - 04/01/09 02:31 AM

Quote:

My '68 V200 gets 25mpg at 65mph. 225, 904, 2.94peg, 185x13 tire

What is a V200?

Quote:

I have a 225 in a 74 Duster automatic with 2.7 gears and it gets 20-25 which is about the same as my 94 Chysler New Yorker with the 3.5.

Mitch

Have similar cars. 225 in a 65 Belvedere and a 94 LHS. Nice thing about the 65 is even if you city drive it and drive it hard it's still gets 20 mpg. Mid 20s are average for highway and our best tank is a straight Full to Empty at 70 mph, was 26 mpg. Odometer was confirmed against GPS.

As for comparing it to the LH with a similar size engine. Our mileage is also around the same numbers. I've seen the mileage in the teens when city driving the LHS but have also seen 29 straight highway. The biggest difference is the performance. 65 ran a 19.9, the LHS is 15.8 in the 1/4.

Posted By: dOrk !

Re: slant 6, fuel mileage. what should i get? - 04/01/09 02:37 AM

Quote:

my bone stock '76 with a 225 1bbl, A833OD, 3.21 gears and 25" tall tires knocks down 19-22mpg city, 25-28mpg highway with a best of 32. a lot of people actually report marginally BETTER mileage after retrofitting the super 6 2bbl setup...

Better MPG than 32 ? .... roger that.

Anyone remember a biz called SVI ? ... they did muchO bester !

Posted By: moparmarks

Re: slant 6, fuel mileage. what should i get? - 04/01/09 02:58 AM

Fact: The 1976 Feather Duster and Dart Sport Light with the 255/883OD were the first US cars to get over 31mpg.
My 75 Dart Sport with an auto got 27-28 highway all day long. My 79 B200 w/ 318 883OD and 355 gears got 25 highway.
If your getting under 20 in an A-body then something is wrong.

Posted By: Rug_Trucker

Re: slant 6, fuel mileage. what should i get? - 04/01/09 04:00 AM

The best I ever did was 29.5 with my 72 Duster. 1bbl 198 long rod short stroke with 3:23's and a 3 speed manual. Usually got 25.4 highway. This is running pump 93.

I added a Holley 2bbl from a 318 headers, .090 off the head, lots of porting, really tight lash. It dropped to 22mpg.

I swear the 2:74's or 2:76's lug the slant and suck the gas.

Dad had a 73 Valiant 4 door that got 13. Slush box PS and air.

I was getting about 16 with my 74 auto 2:76 PS 4 door Dart. I reset the lash tighter than stock, tuned it and got 18+ before it sucked a rag into theoil pick up

I have a post with pics running right now.

slant 6, fuel mileage. what should i get?