3.55's or 3.73's at least with a od 833
What's the absolute maximum range of your Duster?
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Good engine! Would do well for you, for sure!
Do you know what rpm you cruise at and at what speed that would be? Thanks.
cruiser
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Mike, my original owners manual shows a 16 gallon tank. This photo is from page 52 of the manual showing the fuel capacity. In any case, it's a pretty small tank.
cruiser
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I don't have a tach, so I wouldn't know what the RPM is at 70 mph. Sorry I can't help with more info.
cruiser
Well-Known Member
No, I'm trying to keep it all original, but I know a lock up would probably help. Thanks.
You didn't say in your original post what year Duster you had. I looked up specs on a 70 in factory spec info on the Hamtramck site.
cruiser
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99K miles on engine. Last tuneup was last fall, replacing all the stuff you mentioned. Engine fires right up, and plugs show light tan coloration.
cruiser
Well-Known Member
Yeah, you're right. Mine's a 74. Guess I was assuming all Dusters used the same tank. They likely put a smaller tank in as the gas crisis deepened into the mid 1970s. Smaller tank equals less weight being hauled around.
On a stock slant that's true. On a modified one not so much. Also too, the final drive ratio has a LOT to do with it. People put an OD in something with a 3.23 or a 2.76. What do you expect? You need at the very least a 3.55 and more like a 3.91 or 4.10.
I think you need to take a deep breath and approach this from a diagnostic standpoint. Put a vacuum gauge on it. What is the reading at idle hot? WHERE is the initial timing set? WHERE is the total timing? Plot that curve in a graph and look at it. A stock slant should have close to or over 20hg of vacuum. If it doesn't something's wrong. That car should be knocking down 20 plus MPG, IMO being driven conservatively.
Also, what's you tire pressure? Setting pressure by what the owner's manual or the sticker on the car is a mistake. Those pressures are for bias ply tires AND for best ride quality, not for best wear. The maximum pressure on the side of you tire is what you should run. It's probably 35PSI.
This ^^^ Something is killing the gas mileage. A plugged Cat ?
yellow rose
Overnight Sensation
That’s exactly what my car looks like. And yes, yellow is the fastest color. That has been scientifically proven.
No it hasn't. Red is the fastest color. Just ask any insurance company. Man you got lots to learn. dummy. lol
I agree with a few of the previous posters, the whole point of the overdrive is to be able to use some lower gears to make 1,2 &3 really rock and then be able to cruise on the highway at a reasonable rpm in OD 4th. A set of 3.91s would be like a set of 3.23s with a non-od trans. Once you tried it, Oh Princess, I bet you'd love that transmission!
A 3.91 will be a 2.85 final drive in OD.
Piggly Wiggly? I'll be stopping at our Piggly Wiggly today. The O/D works better with lower gears, 3.55 or 3.91. That keeps the ratio around 2.76 which is a nice highway gear. O/D is highway cruising gear. Use it like a 3 speed until you hit the highway.
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I'd adjust the valves, and I think those years were jetted lean. You might want to try jetting richer a step at a time. Your electronic ignition will work great, nothing better. Check to be sure your vacuum advance is working. Play with timing, trial and error, and see if you can't get better power and mileage. Also get a vacuum gage and cruise at the highest vacuum for your given speed. We used to go 300 miles per stop V8 or /6. You should be able to get 20 mpg. I used to work at Chrysler up to the mid 70's. I loved those A body cars.
I don’t remember a ‘74 Duster (I owned one w/a 318) having catalytic converter(‘s) on the exhaust. Just a muffler and resonator. Perhaps Cali Dusters had them. N.Y. did t follow Cali car equipment until much later.
I guess if so equipped, a partial collapse would do it.
I’d believe that one. Just because it’s odd.
I think it’s actually that RED gets into the most accidents.
No problem. Then as I said earlier, I do believe that a retuning of the carb & distributor for Max Benefit in the mileage seeking would be where to start with a recurve of the distributor and then a fine tuning of the carb. Tweak tweak tweak!!!!
Best of luck in the search!
@Princess Valiant (Or anyone else wondering about a OD trans swap and the effect it has on the final drive ratio for mileage.)
In order for the OD trans to work best to equal or better the mileage your getting with the current 2.76 gears, the below calcs were done to show the needed gear ratio to better mileage.
4.01’s & 3.91’s are out since they are numerically higher than your current gears. Current ratio - 2.76
(Edited with a reminder of the wrong ratio first entered, thanks to 66fs.)
(4.10’s added in. Ratio’s in parentheses on the right all with the .71 overdrive ratio.)
2.76 X 1-1 = 2.76 (of course)
4.10 X .73 = 2.99 (2.91)
3.91 X .73 = 2.85 (2.818 /.71)
3.73 X .73 = 2.72 (Winner) (2.648/.71)
3.55 X .73 = 2.59 (2.52/.71), (2.59, loser, lethargic as you stated.)
Now back to our original thread topic.
In order for the OD trans to work best to equal or better the mileage your getting with the current 2.76 gears, the below calcs were done to show the needed gear ratio to better mileage.
4.01’s & 3.91’s are out since they are numerically higher than your current gears. Current ratio - 2.76
(Edited with a reminder of the wrong ratio first entered, thanks to 66fs.)
(4.10’s added in. Ratio’s in parentheses on the right all with the .71 overdrive ratio.)
2.76 X 1-1 = 2.76 (of course)
4.10 X .73 = 2.99 (2.91)
3.91 X .73 = 2.85 (2.818 /.71)
3.73 X .73 = 2.72 (Winner) (2.648/.71)
3.55 X .73 = 2.59 (2.52/.71), (2.59, loser, lethargic as you stated.)
Now back to our original thread topic.
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Correct. Chrysler's ran so clean that some 318 cars did not get them till 1976. All the rest started in 1975. Convertors will actually plug up.
75-76 O/D final ratio is .71. While 77-up O/D ratio is .73. The rest is correct.
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