Hello slant six. I got myself a 74 dart slant six and I want to increase my gas mileage.
It's an old motor and it seems as if it does not get good mileage for what it is.
I plan on figuring out when I get the chance, how much mpg I'm getting by writing the fuel use down, along with my speedometer reading, then filling it then when I get to empty do the math.
How can I increase milage? I bought a new filter, new spark plugs, a new voltage regulator (it died) and replaced the distributor cap and rotor. What can I do to help my mileage?

Also I'm burning oil. Uh oh whats your thoughts on this? I need to replace the tranny pan gasket I know that. But I can't see where I'm losing oil. What's your thoughts and ideas? Thank you for taking time to read this post.

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1974 Dodge Dart Swinger

Welcome to the board!

You'll find many articles on gas mileage by using the search function on this forum.

Your '74 should get you anywhere from 20-24 MPG, maybe even a bit more, depending on how you drive it and what state of tune it is in.

What is your current MPG?

How many miles are on this vehicle?

How much oil are you losing every 1000 miles?

Have you changed your PCV valve?

Give us those answers and we'll be glad to help you!

- Mac

Welcome on the board. You'll want to get the three books listed in this thread as quickly as you can -- they are your first, second, and third most important tools for successfully and economically diagnosing, repairing, and improving your car.

Tune-up parts and technique suggestions in this thread. The engine requires periodic valve adjustment. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Once you've got the engine in tip-top tune, that will establish a baseline from which to work towards improved mileage.

Are you burning oil (blue smoke from the tailpipe) or leaking oil, or both? If you're burning oil, the engine is mechanically tired and won't give you good mileage no matter what else you do; it would be time to look for a replacement engine or look into having yours rebuilt.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Oh please, how can you tell somebody that they should get this type of mileage when these cars could hardly get 17mpg when they were new.

Not on this planet, unless he's coasting from here to Hell with the wind at his back (or his odometer runs about 40% fast).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

My '68 regularly gets me 21 mpg, with a VERY tired slant. My 74 (long gone) always ran between 22 & 23.

Yes, 24+ would be ideal, but it's not impossible.

But if 17 MPG is optimum for A-bodies, running in factory-fresh tune on this planet, then by all means, shoot for that.

- Mac

You're on the far right end of the bell curve. It would be interesting to see how accurate your odometer is.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Just to add in my experience, with a mix of city and highway mileage and top highway speed of 60-65, I get about 16.2 MPG, pre HEI upgrade and 2-1/4" exhaust overhaul.

Hopefully noticeably better after those two adjustments.

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<img src="http://i91.photobucket.com/albums/k286/Krytellan/Vehicles/view1.jpg" border="0" alt="Photobucket">

Since when did 20-22mpg or so become unrealistic? I thought thats what the norm was for a well tuned stock slant? I've done just about every upgrade you guys have mentioned these last few years (super six, nos carb, 2 1/2" exhaust, HEI etc) and I've gotten 20-22.5mpg at every fill up. My engine isn't tired out though, it has about 30k on it.

I start getting skeptical at numbers that are above 24. I figure if I can get 22mpg once in a while with a 904 tranny, then it wouldn't be out of the realm of possiblity to get 24mpg with an 833 OD.

I'll check and see if my odometer is working correctly but I don't see why it wouldn't be. Nothing has ever been messed with as far as that and the speedo gear goes.

Dan, what mpg's are you getting right now?

Go dig through old magazines and look at what these cars got when they were brand new. It wasn't any 22 mpg, let alone 24+. With everything in tippy-top tune and some efficiency-improving mods (exhaust, ignition, distributor, etc.) and an optimal match of rear gears and tire size to highway cruise speed, 20-22 moves into the window of realistic expectations, but a stock '74 A-body complete with tiny exhaust system and sluggish distributor advance curve is highly unlikely to get that kind of economy. Even the lightweight non-smog early A-bodies didn't get anything like that kind of fuel economy, though in that case the main factor was less-than-completely-reasonable rear axle ratios. I'd expect to see really nice MPGs out of an early A-body retrofitted with a 2.76 rear axle and the aforementioned efficiency mods.

My '73's fuel economy sucks right now because the timing chain is stretched and therefore the cam rides the short bus. Ask me again after the new engine goes in.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Yeah that makes sense, 20-22mpg should be what you can end up with by doing all the required mods...not what you would expect to start with.

I'm curious as to what one could get out of an early A body with the right tire size, highway gears, exhaust, correct engine build and 833 OD transmission. Surprised no one has done a full on MPG build yet. Ted has one thats close but he doesn't have an early A and I don't think he has an overdrive either.

We have consensus!
Probably quite excellent, given the MPG figures turned in by the heavier Dart Lite and Feather Duster. The big variable is what we consider "correct engine build". I think a thoughtfully-engineered and -tuned fuel injection system on a thoughtfully-built 170 engine has real prospects…

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Indeed.

The Feather Duster broke all sorts of slant six MPG records at the time, didn't it? 32mpg highway?

Better than my Toyota Camry!!

http://www.slantsix.org/forum/viewtopic ... 2a502397a8

Having had several 225 /6 A-bodies as daily drivers for over 10 years, I usually got a best of 19-20 mpg in summer (mixed driving), while in the dead of winter mpg dropped to 12.5.

In theory I should have gotten slightly better on highway driving, but anytime I'd drive any serious distance, I'd end up going 75+ mph to keep up with traffic.

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63 Valiant Wagon
225 - 4 bbl

My '74 Valiant used to pull down 23-24 all the time with the stock engine. An Offy / 390 Holley tuned in, and a bit of distributor recurve. Your there.

You can do it with a 1bbl, but your going to work harder at it. The good news is, with a stock engine, the 1bbl car will be quicker!

CJ

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Part of Tyrde-Browne Racing