Hi all, I'm getting a 1976 Dart 4-door with slant-six 225, 1-barrel carb, automatic transmission. I'm going for fuel economy improvement only. not power. I've read different sources on improving the fuel economy on the slant-6, but they also include getting more power which possibly lowers the economy? What can I do to get better mileage only? Is changing to a 2-barrel carb better or worse, and is the bigger exhaust (2 1/4") just a matter of connecting a bigger pipe to the existing manifold? Is milling the head for higher compression an improvement for mileage?
I've wanted a Slant-6 for about 23 years now, and it looks like I'm finally going to get one. The main purpose is for reliability and easy backyard-mechanic work. I am done with newer vehicles with all the electronic sensors, computers, etc. I can live with slant-6 electronic ignition module, but that is it.

Thanks for any help!
Jeff

In 1976 the Dart Lite was released. This car was made as light as possible with an aluminum hood, trunk bracing and bumper brackets. An aluminum intake manifold, a specially calibrated carberetor and distributor, economy rear axle ratio, TorqueFlite automatic or A833 4-speed manual overdrive trans... A dual biscuit catalyst was utilized and a new larger exhaust system. The Dart Lite was rated by the EPA at 36 mpg. The Plymouth version was the Feather Duster.

I would see if you could find some of the aluminum items to make yours as light as possible, enlarge your exhaust system...go to an overdrive tranny and go with the electronic ignition.

Welcome on the board. Think carefully and plan out your specific goals before you do anything; be careful not to spend so much money on modifications that you never make back the expense in saved fuel. Unless you plan on driving this car on the highway at high speeds a lot, swapping to an overdrive transmission probably falls into the "more money and work than it'll ever be worth" category, because it's a lot of work and requires a lot of parts.

There are lots of options for almost every category of modifications you can make to that car. You can bolt a 2#&188;" headpipe to the stock exhaust manifold (they're all the same size) — that's what the factory began doing on some slant-6 models in '76 and most of them in '77 — or, if you have the money and want to improve things even further, get Dutra Duals and build a good exhaust system off of those.

The 2bbl setup can give better mileage and performance than a 1bbl setup, but this is not always or necessarily the case. It depends on how the particular setup on the particular car is configured. How do you intend to use the car?

There are improvements to be made not just in the intake and exhaust, but also in the ignition and various other departments, too — your '76 already has electronic ignition from the factory, but there are upgrades to the spark-making components and you can adjust the distributor's advance curves for max driveability and economy.

Will your car have to pass any kind of emission test? If so, what kind (be specific)? Where is the car registered? How many miles are on it, and what kind of condition is it in overall? If there are enough miles on it that the timing chain might be stretched and/or other parts might be worn, then your money and effort will be best spent renewing worn parts at first.

Get the factory service manual, check to make sure that indicated TDC is actual TDC (the crank pulley can slip so the mark's no longer accurate), do a careful tune-up, and adjust the valves. One thing to check: Does a vacuum hose run directly from the carburetor to the distributor? Or does it go from the carburetor to a widget on the air cleaner housing, and from there to the distributor? If so, reroute it so it runs directly. This will significantly improve driveability and mileage.

If you'll post a clear, sharp, full-frame picture or an accurate transcript of the car's fender tag (a 2" × 3" metal plate full of letters and numbers on the driver's side inner fender), we can tell you details about the car's construction and equipment.

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

The Dart Lite and Feather Duster pieces are nice, but very rare and expensive these days. here are some more realistic things you can do to improve the fuel economy of your slant six:

(1) A good tuneup. Don't forget the basics. Read this thread to find out the best parts and techniques to use. New cap, rotor, plugs, and air filter. Don't waste your money on K7N stuff. A napa gold air filter flows just as much air and filters just as well.

(2) adjust the valves. this thread tells you how. Well adjusted valves are critical to how a slant six runs.

(3) Upgrade the exhaust. Increase your entire exhaust line from the exhaust manifold to the tailpipe tip to a 2 1/4 inch system with a free flowing muffler. This will produce a noticeable improvement in power and economy.

(4) Route the vacuum advance hose from the distributor vacuum advance pod directly from the distributor to the ported vacuum port on the carb. basically just bypass the OSAC valve.

(5) Clean and lubricate the distributor. At this point in your car's life, chances are the distributor springs are no longer operating freely. The original grease has probably crusted up and keeping the springs from operating smoothly. Clean them and relube them. While the distributor is apart, make note of the numbers staped on the governor and the vacuum advance arm. These might be important later.

(6) Check for vibration dampener slip. The outer ring on the vibration dampener is where your timing mark is. After 30 years, chances are the outer ring has slipped from its original location, but maybe not. I once worked on a 1976 motor wjhere the vibration dampener had slipped and the tmiing mark read 8 degrees retarded. Point is, all the careful efforts of timing the motor properly will be wasted if the timing mark isn;t accurate.

(7) Clutch fan/electric fan. These are proven ways to increase your MPG. Clutch fans are cheaper and easier, and work nearly as well as an electric fan.

(8 ) Cold air intake. It is fairly easy to get an air cleaner from a later model slant six vehicle (late 70s/early 80s) which has a provision for a cold air intake, or you can modify your original air cleaner. Supplying the motor with cooler, denser air is another proven way of improving both performance and MPG. Don't go nuts like the import crowd does. A dryer hose and some gutter flashing bits can be purchased at a home improvement store and work well to duct cold ait to the air cleaner.

(9) Rebuild/replace the carb. A throrough and high quality rebuild and proper adjustment of your carburetor is key. Rebuild the original carb, don't buy a rebuilt one. If you don't feel comfortable rebuilding it yourself, ask for a recommendation of where to send it to be rebuilt. Better yet, order a brand new Economaster carburetor from SlantSixDan. Pricey, but these are carbs specially designed to improve fuel economy. Finally, make sure that whatever carb you use is properly adjusted and functioning. Make sure the chokeis set right, make sure the choke pulloff diaphragm isn't ruptured, etc...

(10) Run stock rims and tires. Skinnier tires offer lower rolling resistance. Resist the urge to look cool with fat tires.

(11) Make sure the transmission, especially the kickdown is adjusted properly.

(12) Check for timing chain stretch. Agauin, a 30 year old motor probably has some worn components. Factory slant six timing xhains had NYLON coating the teeth. As you can imagine, this wears off and the chain stretches. This leads to unreliable and late timing events.

(13) Swap ignition to HEI. This is actually a fairly simple and cheap ignition system upgrade which will improve performance and economy, a smidge. Do a seach on the board. This has been discussed many times before.

(14) Check for vacuum leaks. A stock slant six in good tune with no vacuum leaks should get above 16 inches of mercury at idle. My brother's van got 21 when I was done tuning it up. More vacuum is always better. In fact, one of the best things you can do to improve fuel economy is to install a vacuum guage and adjust your driving habits to drive to achieve maximum vacuum at all times.

(15) increase the gap on your plugs. This is especially good if you upgrade to HEI. I always gap my plugs to .045. This make a little bit hotter spark, which might give you better fuel economy. Then again, I might just be deluding myself.

(16) make sure the heated air intake system is hooked up and functioning on your car, especially if you live in a colder climate.

(17) Many people report that switching to a two barrel carb improved their fuel economy. I would suspect that some of the increase in fuel economy came from replacing a worn out carburetor with a fesh one and eliminatingvacuum leaks, but is the engine makes more power with less throttle opening then you can increase your fuel economy too. Personally, I recommend keeping your one barrel and getting an economaster from Dan.

That is all of the easy ones I can think of right now. I am sure others will chime in with more ideas.

Welcome to the board, feel free to ask more questions.

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Casually looking for a Clifford hyperpak intake for cheap.

Wow, thanks guys. That's a good start for me.
I'll try to get a good picture tomorrow. I'll also get a better idea of the mileage/condition then. The only picture I have now is one of the side of the car. My location is Ponce, Puerto Rico, and the driving is strictly daily transportation at an average of 55 mph after we get out of the city. I can't give a detailed emissions regulation yet. All I know is that they connect a hose to the tailpipe, run the motor at a specific RPM for a minute or two and read the findings on a computer screen. They do that with our 89 Ford Crown Vic, 95 Caprice, and the 89 Ford F150 I owned in the past. They take longer on the newer vehicles I noticed, and have seen them get in mild arguments with the owners on more than one ocassion, which leads me to believe that the newer cars have a stricter emissions regulation than older ones here in Puerto Rico. Unless the owner is seriously wrong about the overall condition, I should have the car on Monday. I plan on keeping it forever and simply replacing/rebuilding parts when necessary. I just wasted $400 into repairing my 95 Chevy Caprice which had a fried ECM unit, only to have it go bad again in one week. Between that and the other multiple electronic devices and sensors, I decided to get what I've always wanted: an older Slant-6, and say goodbye to the modern gasoline-powered computers-on-wheels FOREVER. That's just me, I guess I'm a minimalist when it comes to mechanics; the less "stuff" the better. Considering the Slant-6 motor can get comparable mileage to 4-bangers today, it makes a lot of sense to me to get one. Not sure if the link will work, but here's a picture of it below.

http://forums.qrz.com/attachment.php?at ... 1227385563

kp3ft,

I agree with you on the complexities of modern vehicles and have become a minimalist as well in terms of vehicle choices. When ever I get in my 69 Chrysler 300 (with a 375 HP 440) and step on it I can't help but smile. My wife drives a beautiful 72 Imperial for safety reasons, she was nearly killed in our Chevy Sprint after being hit head on. I drive a highly modified 74 Dodge Dart Swinger. It is a car I always wanted since I was a teen. I drive it about 120 miles a day and have allot of fun with it. Sometimes simple is good!

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG