MPG experiment....1976 Dart Lite

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Backtobasics

Backtobasics

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I have an almost stock Dart Lite. 225 /6 with 3 SPEED and 7.25 rear end.
The car is manual steering, manual 4 wheel drum brakes, and very little options (3 speed wiper and 3 speed transmission were only primary options) Only "upgrades" so far are the modern radial tires, and a "dual" exhaust that splits into a Y where the stock converter would have been, through glasspacks out the rear. Exhaust is in line after carb, and distributor modifications, with a GOOD dual or bigger single system with better mufflers.

Since this was Dodge's MPG car, that is what I am going to start to do...Tune it for better mileage.

As run, it has 15" ralleye wheels, small bolt pattern. The drum brakes have been gone through COMPLETELY, and now stop EXCELLENT.

Dart has received a basic tune up consisting of:
  • plugs
    wires
    cap
    rotor
    fuel filter
    air filter
    oil change
I adjusted the valves to quiet it down, i still have one or 2 that are clacking, so I need to go back with the feeler gauge, and get them adjusted properly.
I also had to run the idle a little higher then I would like to make driving easier, as it would not leave a stop at low idle. Investigation led me to no accelerator pump function.
First full tank, of 35% in-town driving, and 65% highway, (with stop and go, but most highway is 35-55 consistantly) MPG was 13.5

Long Terms goals:
I am going to swap the 4Speed OD that I bought with the car, once I have maximized MPG in the current configuration. I also bought 8 3/4 rear with 3.55 (3.23 also available) rear end that I want to go in later. Eventual plans are Turbo stock /6, and 8.75 may wait until then, or in sooner if the 7.25 gives up sooner.
 
Next phase, next tank:

I am going to start with Carb. Mileage on odometer says 41K, so presume is 141K.

I started with carb teardown. There is extra "Stuff" on it. I will post pictures later. During teardown, I noticed coat hanger material wrapped around the choke shaft, and throttle shaft, several times. WTF.
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As I tore into it, I found 2 of the 3 bolts that hold the carb base to the carb main body were stripped.
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So I took off the extra "stuff" and separated main body / upper body / base, and set them into the carb soaker cans. Main and upper look AWESOME
I am going to tap out the main body, to a larger size for new fasteners, and rebuild carb, then run for next MPG update.

Next up is to start with some of the distributor and ignition modifications.
I think the HEI will be next.

Ideas are welcome, some might be tried some might not.
 
Just a few points to make sure you get an accurate base. In the process of doing the same thing to a standard Dart.

I would verify what gear is in the rear now, tyre size and make sure your speedo gear is the correct one. No sense in jumping through hoops trying to get mpg maxed when your numbers are skewed by being off.

There is a lot of discussion (sorry to talk about another board) about this same subject on the slant board where I have picked many a brain and read through posts for hours. Some great info!

First thing I'd do is get that carb repaired. You may just flat have a dud. Some quickie obvious things, but if the choke is not working correctly and not openning right then you are going to use more fuel. Parts missing? Wrong carb for car? What kind is it?

Does the car have any vacuum leaks?

Plugs and gap used?

Timing currently?

What rpm at 55?

Vacuum readings?

Total timing at 55?

Tyre pressure?

What do plugs indicate mix wise?

There are some starters.

Exhaust wise, seems the most popular upgrade if not going to DDuals or a header is to use a 2.25 pipe back from the exhaust to the muffler. A good quality muffler and then out the back with a 2" or stock 1 7/8". Very popular upgrade to standard exhaust and what I'm about to do.

Gearing wise that is up to you. Sounds counter productive to the goal of MPG as the turbo and increased gear sound more directed to performance and power. Granted, you can get those and still keep mileage, but depends what you really want out of the car. The 4 OD will help keep that under control though rpm wise while cruising I guess.

The car I picked up was probably getting 7 or 8 mpg for the previous owner. Bad state of tune, neglect, carb in poor shape and smoking fuel out the back etc. Basically did what you did above and rebuilt the carb and the car got 11 mpg. Started playing with timing, did the HEI and tuned the carb (1bbl Holley) and in general around town driving got 16.9mpg. Now have the pieces to recurve the dizzy, etc. so that is next as I've mapped out my advance curves and they are not the greatest in the world. Should get that fixed next week.

Oh, numbers are at just under 6000 feet elevation, 225, 904 auto, corrected speedo, 3.21 gearing and 225/60/14 tyres with PS & air (not running air during mpg tests).

Best of luck with it and perhaps see you on the slant board also.

Cheers
 
13.5 mpg for combined is pretty poor, I would say you have some issues with the timing and/or the carb.

I got 19-20 around town and 21-23 with a \6 with a comp Cam, offy intake, 390 cfm 4bbl, headers dual exhaust, A833OD and 3.55 gears.
 
dgc333 said:
13.5 mpg for combined is pretty poor, I would say you have some issues with the timing and/or the carb.

I got 19-20 around town and 21-23 with a \6 with a comp Cam, offy intake, 390 cfm 4bbl, headers dual exhaust, A833OD and 3.55 gears.
Click to expand...


I agree. 13 is terrible. The point of the post, and direction is, to incrementally make it better.

Right now, (before I took the carb off) it would start instantly, idle was pretty smooth (8 out of 10 by comparison to new car) and pulled excellent. However, leaving a stop light was a different, it did not like it, probably due to the non-functioning accelerator pump. So average person would see this as "good running car" yet it only gets 13.

I want better, much better. The carb was the biggest fault, so that is why it is first.
 
MoparBrit said:
Just a few points to make sure you get an accurate base. In the process of doing the same thing to a standard Dart.
There is a lot of discussion (sorry to talk about another board) about this same subject on the slant board where I have picked many a brain and read through posts for hours. Some great info!
Gearing wise that is up to you. Sounds counter productive to the goal of MPG as the turbo and increased gear sound more directed to performance and power. Granted, you can get those and still keep mileage, but depends what you really want out of the car. The 4 OD will help keep that under control though rpm wise while cruising I guess.
Click to expand...

You are dead on to the direction.

I am going to start with the basics and go from there. I am going to get it into a basic state of tune. It was getting the 13 mpg with the body of the carb coat-hangered to the base plate.

I intend to try most of what is on your list. Gear and speedo confirmation is coming shortly, after the carb is installed.

I don't think the carb is junk. I just think that the moron who rebuilt it last overtightened the screws that connect the base to the main body. A quick cleanup, drill and tap, and some good screws to put it back together.

/6.org....I have a post over there too. I expect them to have some input too.

I am in the early stages. I need to get a tach, so I can see what RPM is, I need to get a vacuum gauge, so I can see where max vacuum is, etc.

I will post the MPG results after the rebuild carb is installed, and then work from there.

The goal is to be solid overall performer. Turbo can cost mileage to be sure, but that is under my control with throttle, and it might be a while, likely that is a winter project. Overall goal is efficiency, which translate to fuel economy. Turbo will be minimally invasive, if sized right, and almost non existant during cruising other then an exhaust restriction. The heat from the turbo and subsequent improvement in fuel atomization, will likely offset the exhaust restriction, yet allow, at the touch of the throttle, more horsepower, as needed.
 
Mine was an "OK" runner but was also getting about 13mpg on the hwy when I first got it running. It turned out that I had many vac leaks and the carb was adjusted rich enough to almost overcome the lean condition. I'm happy to say that it gets 20-22 mpg on the hwy now ( at 65-70 mph :) ) and I'm running a 904 with a BBD carb. Now I'm not going for mpg but I'm definitely not going to make any mods to make it worse
 
Yes, 13MPG is very poor and you should be able to improve on that greatly. If I am correct, the Dart Lite and Feather Duster were rated at 34MPG. Heck, my 383 has 11.5 to 1 compression and a 528/284 solid cam and I can get 10
MPG to 12MPG with 3.54's if I baby it.
 
If I recall, it was up to 36 MPG highway with the 4 speed od. I would LOVE to be there. For now, increase in steps, and then when it appears the tune is limited to RPM of the 3 speed, step to the 4 speed OD.
I essentially want to be able to document, 3 speed to 4 speed overdrive on a well tuned ride. I see people who step to the 4 speed OD, but I wonder how much MPG is left, where maybe the 4 speed is masking another possible improvement in tune.
Hopefully have the carb back this weekend, for an update next week....?
 
2nd round has begun. I filled up Tuesday Morning.

1. The carb is rebuilt and installed, with the exception of the accelerator pump rod, which needs to be fiddled with. I am running one of a Thermoquad, as the carb did not have one upon purchase. All of the bolts holding the baseplate to main body, and top plate to main body have been tapped out and have new bolts.

2. Tire pressure has been adjusted to 35 PSI on all 4 corners. I wanted to leave it alone for the purity of the test, but could not in good conscience leave them as bought. Even thought they looked fine, they ranged from 15-18 PSI Tires max pressure is 44, so I might run them up to 44 down the road to see the effects. The manual steering is much easer now, I can almost turn it one handed.

Conclusion, I will fill up Thursday evening, and compute mileage. I now have a book, to keep MPG and notes. Update soon.
 
UPDATE​

I could not wait until this afternoon. I topped off at same station, same pump, with same routine. 54 miles on 2.97 gallons = 18.18 MPG.

Previous was 13.5 mpg.

Adjustments made between 13.5 and 18.18 was tire pressure, tires were under-inflated and the carb was rebuilt. Basic parts store rebuild kit, on a 1945 Holley.

Stock, this car had 6.95 x 14 tires, which converters to 25.3 OD if I understand correctly. Currently, tires are 235/60/15, which convert to 26.1 OD. 26.1 / 25.3 = 1.03 or 3% taller tires.

This changes the baseline to 13.9 MPG, and the current to 18.72 MPG.

Next up: Identify gear set, and fluid change in both differential and transmission. Who knows how much better it will shift and drive with new fluid.
 
you aren't going far enough to really be accurate. at that level if you had gotten in only .3 gallons more your numbers would be way off what they are now.

you need to get into the 10 gallon or so fill-up range.
 
Backtobasics said:
UPDATE​

Next up: Identify gear set, and fluid change in both differential and transmission. Who knows how much better it will shift and drive with new fluid.
Click to expand...
This is one of the little things people forget. Reducing drag to a minimum any way you can. Go with all synthetic lubes. Make sure all of your wheel bearings are fresh. Make sure none of your brakes are dragging, even a little. Make sure your front end is aligned as perfectly as possible and your tire pressures are correct.

Electronic ignition is a must. A multi-spark ignition would probably help some but will not make a huge difference if you tune a standard ignition well. Reduce intake restriction with a K&N or similar filter. All the little things matter. You can realistically get that car up close to 30MPG if you just keep doing what you are.
 
Mine's a 273 with dual exhaust, 10 - 1's, mild Isky cam and a 2V and gets 21 MPG.
 
MPG on the last tank, 19.60 per odometer, 20.18 corrected for tire size.
This was combination of city and highway. AM highway was cruising at 55 MPH for the most part. PM highway is more slow and go, 25-35 mph average.

Changes....
Transmission fluid (drained out 5 ounces, took 85 to fill it back up )
Differential fluid (ok fill level but dirty)

Both were done mid tank, so their benefits were partial. I was hoping to get new exhaust run this weekend, but it might not work with finances.

Next up will probably be the HEI ignition modification. I am also going to duct air up to air filter housing, to see if that helps.

I am not quite ready to dive into the timing modifications just yet. I have to work my way up to that (new, scary )
 
ptowntsi said:
you aren't going far enough to really be accurate. at that level if you had gotten in only .3 gallons more your numbers would be way off what they are now.

you need to get into the 10 gallon or so fill-up range.
Click to expand...

Regardless if I let the tank run dry, or run it for 1/4 tank the point is I filled completely, ran it, and filled completely, and then calculated. 18.72 corrected on last tank, versus 20.18 corrected this tank, taking into account the changes made validate the 18.72 tank run.
 
2shelbys said:
This is one of the little things people forget. Reducing drag to a minimum any way you can. Go with all synthetic lubes. Make sure all of your wheel bearings are fresh. Make sure none of your brakes are dragging, even a little. Make sure your front end is aligned as perfectly as possible and your tire pressures are correct.

Electronic ignition is a must. A multi-spark ignition would probably help some but will not make a huge difference if you tune a standard ignition well. Reduce intake restriction with a K&N or similar filter. All the little things matter. You can realistically get that car up close to 30MPG if you just keep doing what you are.
Click to expand...

Thanks Dude.​
Trans fluid was NON EXISTENT. I am running standard fluid for now, I will switch over to synthetics once the transmission and rear end get "cleaned out" with the new mineral fluid.
Wheel bearings front were repacked with the front brakes, rear are due to be checked when I switch to synthetic in rear differential.
Tires are all spot on at 35 PSI. Tire sidewall says max of 44, I might work up there later. There is a lot of "opinions" on that matter on the thread on slantsix.org.....:angry7:
I want to rebuild suspension later, throwing sway bars, etc into the mix....I wll have alignment set after rebuild.
Brakes could very well be dragging a little, I went to extremes to make sure this 4 wheel drum car would stop in daily traffic. They will also get checked, and drums turned as part of the evolvement of this experiment.
Air intake is next, going to duct air to stock air box. I am not going to spring for a K&N right now, because it would be a waste of money once the turbo come in this winter. For now, clean paper filters, with a little forced air might help. I can't wait to see the difference between the 3 speed and the OD, to actually document the difference.
 
Backtobasics said:
Regardless if I let the tank run dry, or run it for 1/4 tank the point is I filled completely, ran it, and filled completely, and then calculated. 18.72 corrected on last tank, versus 20.18 corrected this tank, taking into account the changes made validate the 18.72 tank run.
Click to expand...

unless you are filling it all the way up the filler neck, you can still easily be off on that small of a fill up.
 
Great thread... after reading yours I decided to do a mileage check when my exhaust manifold blew the gasket and I found out my carb was just sitting on my intake by about 2 threads.

I also found out that my stock air cleaner with new paper filter seemed to hindering my cars performance and not letting enough air into the carb. I bought a Mr. Gasket chrome 1 barrel breather. I'll use the stock one when I show it and this one if the mileage gets better to drive every day,

I'm running in approx 100 mile increments. 1st pass was 16.6 and I'll probably fill back up in a day or so.

I also just found out today that all of my tires had about 80 pounds of air in them!!!! So I backed then down to 35.

Keep up the good work and keep us posted.

buds
chuck
 
ptowntsi said:
unless you are filling it all the way up the filler neck, you can still easily be off on that small of a fill up.
Click to expand...


This is not going to be a perfect test. I fill up at the same station, same pump, and let it click once, and then gently fill to a second click, and then run with it. This is not laboratory science accurate, nor do I really want to be that particular. I supposed I could have gallons of gas at home and fill until the gas is right at the brim of the filler neck, if I really wanted to be that anal, but I am rightfully surprised I was attentive enough to get a book to keep track, let alone go to OC details.

The spirit of the experiment is to:
  • baseline
  • make changes, with goal of bettering the tune, and efficiency
  • report (successes and failures)
This is a report on my vehicle, with my driving, on my communte, and there are many factors that might influence this, yet the spirit if the exercise is fairly consistant.
 
DBG said:
Great thread... after reading yours I decided to do a mileage check when my exhaust manifold blew the gasket and I found out my carb was just sitting on my intake by about 2 threads.

I also found out that my stock air cleaner with new paper filter seemed to hindering my cars performance and not letting enough air into the carb. I bought a Mr. Gasket chrome 1 barrel breather. I'll use the stock one when I show it and this one if the mileage gets better to drive every day,

I'm running in approx 100 mile increments. 1st pass was 16.6 and I'll probably fill back up in a day or so.

I also just found out today that all of my tires had about 80 pounds of air in them!!!! So I backed then down to 35.

Keep up the good work and keep us posted.

buds
chuck
Click to expand...

80 LBS ! Holy Time BOMB, Batman.
 
Im not trying to hinder your experiment, but it would give you more results to analyze if you drove longer distances between diagnostic/parts changes.

I'm following this thread closely because I'm a bit of a mpg nut too.

I get 53 on my street bike and average 17 half city, half freeway in my 5.9L Jeep.
 
ptowntsi said:
...if you drove longer distances between diagnostic/parts changes.
Click to expand...

I would love to be able to run several tanks per modification, but that is not feasible for a couple reasons.
  1. My commute is not that long, I can run a tank of fuel over a 2 week course if I drive it 3-4 days a week. I would be updating once a month if I did this, and the thread, and my personal motivation would die off.
  2. If I was going to put hundred and hundreds of miles between upgrades, I would be doing a dis-service to myself, environment, and the entire principle, by running lots of miles in an in-efficient manner, just to prove the effectiveness of this modification or that one.....
  3. My personal desire to throw all the big/primary/known modifications at the car at one time is too great. I could not bear to only rebuild the carb, and leave the tires low, so I adjusted the tires.
At your suggestion, I am now running almost a full tank of fuel between reports, and noting the modifications for that tank. Some stuff falls in the middle (differential and trans fluid) but I will do my best to enact the modifications at the beginning of the next tank, for reasonably accurate reporting.
 
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