1973 Dart Swinger Gas mileage

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erafuse

erafuse

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Looking for ideas on making my 1973 Dart Swinger easier on gas. It’s a stock 318. Planning on doing a road trip and would like to increase gas mileage.
 
j par said:
What is your combination now? As in rear end gears, kind of transmission, carburetion, exhaust, cam stock, not stock?
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323 gears auto trans 2 barrel carb dual exhaust stock cam. Everything is stock except dual exhaust.
 
toolmanmike said:
Not bad. I get that to about 19 with my 70 Swinger. Not too much you can do that will make a huge difference or cost a lot of money.
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Thanks had a 1973 back in 1973 same car basically only I put a 4 barrel of a 340 on it and a set of headers thought I was getting better mileage but maybe not this one is stock.
 
erafuse said:
Thanks had a 1973 back in 1973 same car basically only I put a 4 barrel of a 340 on it and a set of headers thought I was getting better mileage but maybe not this one is stock.
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What's your initial timing set at?
 
I think your current setup will get the max MPG as it is, 3.23 gears and stock cam is about as good as you can get for mileage (taller gears would do better on the highway but worse around town). I would just do a full tune-up (ignition parts, timing advance, carb tuning) to make sure it's running as efficiently as possible. The dual exhaust is also already helping with MPG compared to the stock tiny single pipe.

You could add a 4-bbl carb and a mild cam for more power but that won't do anything for gas mileage, it'll either stay about the same or go down slightly. A new small 4-bbl carb with small primaries might do better than a 2-bbl but it's a toss-up IMO.

Or dump a few grand in the car for an overdrive transmission and EFI lol...
 
MopaR&D said:
I think your current setup will get the max MPG as it is, 3.23 gears and stock cam is about as good as you can get for mileage (taller gears would do better on the highway but worse around town). I would just do a full tune-up (ignition parts, timing advance, carb tuning) to make sure it's running as efficiently as possible. The dual exhaust is also already helping with MPG compared to the stock tiny single pipe.

You could add a 4-bbl carb and a mild cam for more power but that won't do anything for gas mileage, it'll either stay about the same or go down slightly. A new small 4-bbl carb with small primaries might do better than a 2-bbl but it's a toss-up IMO.

Or dump a few grand in the car for an overdrive transmission and EFI lol...
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Okay thanks. Since the car is stock except for the dual exhaust would like to leave it that way. It’s a great car. Just have to go on short road trips. LOL.
 
MopaR&D said:
I think your current setup will get the max MPG as it is, 3.23 gears and stock cam is about as good as you can get for mileage (taller gears would do better on the highway but worse around town). I would just do a full tune-up (ignition parts, timing advance, carb tuning) to make sure it's running as efficiently as possible. The dual exhaust is also already helping with MPG compared to the stock tiny single pipe.

You could add a 4-bbl carb and a mild cam for more power but that won't do anything for gas mileage, it'll either stay about the same or go down slightly. A new small 4-bbl carb with small primaries might do better than a 2-bbl but it's a toss-up IMO.

Or dump a few grand in the car for an overdrive transmission and EFI lol...
Click to expand...
 
Gear Swap to 2.94s If you have the 8 3/4 rear housing along with the 1406 Edelbrock 4 bbl carb will get you to 20 mpg. Can use the Mr. Gasket 2 to 4 bbl intake manifold adapter, then the intake manifold ports still match the 318 head ports. It's all about smooth port flow and port velocity with these 318s for efficiency and power.

You will be surprised how nicely the 2.94s pull, the tone of the engine will deepen with the 4 bbl on it. Also you will have the secondaries of the 4 bbl to play with when you need more power and excitment.

Works great for me driving around getting to where I am going, great freeway cruising with power to pass other vehicles. Really like the added secondaries of the 4 bbl.

Stock 318, Added 4 bbl carb, 727, 2.94s

One other performance and milage trick is to put on the 100 % light Aluminum Torq Thrust Wheels they are about 20 lbs lighter per wheel than the steel wheels. That is a total of 80 lbs less in rotating mass that you have to spin up every time you take off.

Surprisingly it even brakes easier too because of this.

Happy Cruising . . .
 
I would be happy with 17, back in the day i had 70 ford f250 with a 460, 7mpg, 12 on the hwy.
If they fit you could get larger diameter tires. If you up your rear tire dia by about 10 percent that's the equivalent of going from 3.23 to 2.94. your speedo will be off so you wont be able to measure your milage.
 
Its hard to recoup any investment to increase mileage, cheaper to put it in the tank.

Now if you looking for performance with decent mileage thats a different story.
 
Eg. If you put on 5000 miles a year and could increase from 17 to 20 mpg for $1000 it would take about 7 years to break even.
 
17 is pretty good
With 2.45s and optimized timing you might get 20 or perhaps more..
Just drive slower. Every 1 percent slower speed translates to roughly 1/2% better MPG.
Traveling at 60 instead of 66 is ~10% difference and is apt to increase your mpgs by 5%. Starting at 17 this means 17.85. The same can be said about taking out 10% gear and cruising back up at 66 . So, 2.94s might get you the same 17.85; while 2.76s might get you 19.9. If you combine both, then you can double up eg 10% slower and 10% less gear totals 20% rpm change and therefore 10% mpg improvement.
This only works at "normal cruising speeds" cuz the faster you go the more power it takes to overcome wind-resistance and you can't expect 19.9 at 100mph. But if your 3.23s got 12mpg at 100, then it would again be comparable, and the math says 13.8 with 2.76s.

As to the engine; with 3.23s your rpm might be 2700@65. So you need to optimize your timing at 2700, possibly at the expense of all other rpms. Then you just lean out the carb until it pukes. It is extremely important that your vacuum advance system is working. In fact, this is your primary weapon to getting the timing optimized.
If you have a heated air intake; in PEI, I would tend to keep it . It is designed to keep your inlet air temp to one temperature, namely 85*F, IIRC, so the factory can jet the carb lean and not melt the pistons in winter. Yeah you can make more power without it. And more economy with colder ,denser air, but then you better be careful between the seasons.
And finally, cruise-control sucks in the hills. It will be constantly sawing on the gas pedal. You would think it would average out ok, and maybe it would..... if the accelerator pump wasn't spewing every time, and the metering rods weren't jumping up.
 
George Jets said:
Gear Swap to 2.94s If you have the 8 3/4 rear housing along with the 1406 Edelbrock 4 bbl carb will get you to 20 mpg. Can use the Mr. Gasket 2 to 4 bbl intake manifold adapter, then the intake manifold ports still match the 318 head ports. It's all about smooth port flow and port velocity with these 318s for efficiency and power.

You will be surprised how nicely the 2.94s pull, the tone of the engine will deepen with the 4 bbl on it. Also you will have the secondaries of the 4 bbl to play with when you need more power and excitment.

Works great for me driving around getting to where I am going, great freeway cruising with power to pass other vehicles. Really like the added secondaries of the 4 bbl.

Stock 318, Added 4 bbl carb, 727, 2.94s

One other performance and milage trick is to put on the 100 % light Aluminum Torq Thrust Wheels they are about 20 lbs lighter per wheel than the steel wheels. That is a total of 80 lbs less in rotating mass that you have to spin up every time you take off.

Surprisingly it even brakes easier too because of this.

Happy Cruising . . .
Click to expand...
I had 2.9's in a rock stock 318 auto 76 dart ex cop car w/AC and we got 24-25 mpg freeway, when my wife was driving, hahaha.
 
17 is pretty good. If it was mine, I would put an Edelbrock performer and an Edelbrock 500 on it. A 4 barrell will get better mileage as long as you're conservative with your right foot. A set of headers will also help with mileage and power as well. Also, as mentioned, you can try some higher gears. On the highway, a 3.23 gear with stock, short tires will burn some gas.

First thing I would do though, before dropping a dime would be to make sure your present combination is in optimum tune. That could pick up the mileage a bit right there.
 
17 is good. I've got a 72 Scamp with a 360 / 727, 24" tires on 14" wheels, with a 600 CFM Edelbrock 4 barrel. Holding it to 55 - 60 mph (2,800 - 3,000 rpm) I can now get about 17.5 - 18.0 mpg. That took a lot of tuning to get to that. And I'm putt-putt-putting down the interstate.

So, you're doing good. Spend money elsewhere (my $0.02).


7milesout
 
7milesout said:
17 is good. I've got a 72 Scamp with a 360 / 727, 24" tires on 14" wheels, with a 600 CFM Edelbrock 4 barrel. Holding it to 55 - 60 mph (2,800 - 3,000 rpm) I can now get about 17.5 - 18.0 mpg. That took a lot of tuning to get to that. And I'm putt-putt-putting down the interstate.

So, you're doing good. Spend money elsewhere (my $0.02).


7milesout
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That calculates out to 3.55s in the back.
Same as I had in in the early 2000s. With slightly taller tires I was doing 2600 at 56 mph, for 65=2870. Yur right it took a lotta tuning, even with my nearly 11/1 engine. I finally got tired of putt-putting and stuck an A833od with a GVod behind it. Final drive in double od was 1.97:1 so 65=1600, a reduction in rpm of 45%. According to the 50% rule my mpg shoudda jumped up 22.5%. According to that ,the 3.55s shouldda been returning 24mpgs......... but I never saw that.
I did see a tad more than what you got, probably due to the manual trans. They say a manual is good for 2 mpgs but I never ran that combo as an auto so can't say.
At 2800/3000, I feel for you man. My current combo is at 65=2240, just right for the now bigger 230*@.050 cam. But this 230 is really hard on fuel, and there is nothing I can do about it..
Good job on the 17.5/18
 
Manual trans will help a coupla mpg. 4 speed OD 833 would be even better and would be good with the 3.23.
 
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