1973 Dart Swinger

[erafuse]

Have a 1973 Dart Swinger. What rear end would be in a stock 1973 Dart Swinger? Pretty sure it’s 3:23 gears. On the highway at 60 mph it’s turning about 2000-2200 rpms.20-21 mpg. Would different gears make it better for highway driving and would it be worth the bother to change gears?

 

[Ddaddy]

What size rear tires? Calculations show it’s probably a 2.72 rear ratio, but if I knew the actual wheel and tire size I could give you a better number.

 

[erafuse]

What size rear tires? Calculations show it’s probably a 2.72 rear ratio, but if I knew the actual wheel and tire size I could give you a better number.

Thanks. 205R-14

 

[Ddaddy]

Thanks. 205R-14

Do you know the aspect ratio of the tires? Are they 70 series or 75 series? The side wall should read something like 205/70 14.

 

[TrailBeast]

Have a 1973 Dart Swinger. What rear end would be in a stock 1973 Dart Swinger? Pretty sure it’s 3:23 gears. On the highway at 60 mph it’s turning about 2000-2200 rpms.20-21 mpg. Would different gears make it better for highway driving and would it be worth the bother to change gears?

I think it's probably 2.73:1 gears in a 7.25 rear end.
That's what my 73 has in it, but it's possible you have an 8.25.
I went from 17-18mpg to 25 when I changed to an OD trans and left the rear gears.
(hiway car, not a racer of any kind)

 

[erafuse]

Do you know the aspect ratio of the tires? Are they 70 series or 75 series? The side wall should read something like 205/70 14.

205/70R 14. Tag on rear end looks like 276

 

[Ddaddy]

205/70R 14. Tag on rear end looks like 276

That sounds about right based on your rpm and tire size.

 

[erafuse]

I think it's probably 2.73:1 gears in a 7.25 rear end.
That's what my 73 has in it, but it's possible you have an 8.25.
I went from 17-18mpg to 25 when I changed to an OD trans and left the rear gears.
(hiway car, not a racer of any kind)

Is your overdrive standard or auto? Mine is a stock 318 auto Would like to leave it stock but would like to improve gas mileage.

 

[erafuse]

That sounds about right based on your rpm and tire size.

That sounds about right based on your rpm and tire size.

so probably a 7.25. Any ideas on how to improve gas mileage. 318 2v Auto.

 

[TrailBeast]

View attachment 1715357607 so probably a 7.25. Any ideas on how to improve gas mileage. 318 2v Auto.

Yep 7.25.
I put an A500 overdrive out of a Dakota pickup in mine and built an automatic shifting system for OD and lockup.
If you are doing 19-20mpg you are doing better than most already.
Getting those hiway RPM's down is the key.

 

[Ben Drinkin]

View attachment 1715357607 so probably a 7.25. Any ideas on how to improve gas mileage. 318 2v Auto.

Depends on your budget. Getting the best out of your tune (dist advance, initial timing, carb jetting...) would be step 1. Slightly taller tire help. Possibly an intake/carb swap to a small 4 barrel (or tbi if in your realm) and reduce exhaust restriction..

I'd say tune the hell out of what you have and see if you're satisfied.. after that...

 

[erafuse]

View attachment 1715357607

Yep 7.25.
I put an A500 overdrive out of a Dakota pickup in mine and built an automatic shifting system for OD and lockup.
If you are doing 19-20mpg you are doing better than most already.
Getting those hiway RPM's down is the key.

Thanks. Last time I tryed it was 21 mph.But it varies 17-21 mph. Yes like to get the rpms down.

 

[TrailBeast]

Thanks. Last time I tryed it was 21 mph.But it varies 17-21 mph. Yes like to get the rpms down.

A trans change or an aftermarket OD unit like a Gear Vendors is your only option.

 

[Ddaddy]

Thanks. Last time I tryed it was 21 mph.But it varies 17-21 mph. Yes like to get the rpms down.

I have to ask, why?

 

[erafuse]

Depends on your budget. Getting the best out of your tune (dist advance, initial timing, carb jetting...) would be step 1. Slightly taller tire help. Possibly an intake/carb swap to a small 4 barrel (or tbi if in your realm) and reduce exhaust restriction..

I'd say tune the hell out of what you have and see if you're satisfied.. after that...

Thanks I have a 4 barrel intake of a 340. But with the 904 transmission not sure if it would stand it. I had a 1973 318 back in 1973-77. 318 4 barrel with headers and had issues with the transmission but I won’t be abusing this one like back then. Lol

 

[erafuse]

I have to ask, why?

Do mostly highway driving. Gas is $5.55 a gallon. I don’t drive the car that much so just best to put up with it I guess.

 

[erafuse]

A trans change or an aftermarket OD unit like a Gear Vendors is your only option.

Thanks for the info.

 

[Ddaddy]

Thanks I have a 4 barrel intake of a 340. But with the 904 transmission not sure if it would stand it. I had a 1973 318 back in 1973-77. 318 4 barrel with headers and had issues with the transmission but I won’t be abusing this one like back then. Lol

The 904 can handle it easily.

This engine is a 318, 4 bbl, mild cam, dual exhaust, 3.55 sure-grip rear and....a stock 904 tranny.

 

[erafuse]

The 904 can handle it easily.

This engine is a 318, 4 bbl, mild cam, dual exhaust, 3.55 sure-grip rear and....a stock 904 tranny.

View attachment 1715357617

Okay. What setup do you have in the kick down. Seems you have to have that setup right. I put 3 transmissions in back in 1973. But used to do lots of racing. Won’t be racing this one just cruising.

 

[Ddaddy]

Okay. What setup do you have in the kick down. Seems you have to have that setup right. I put 3 transmissions in back in 1973. But used to do lots of racing. Won’t be racing this one just cruising.

Factory specs on the kick down.

 

[erafuse]

Factory specs on the kick down.

Where would I find info on factory specs?

 

[Ddaddy]

Where would I find info on factory specs?

My Mopar has downloadable manuals and YouTube has old Chrysler service videos on it. It’s very easy to do.

 

[erafuse]

My Mopar has downloadable manuals and YouTube has old Chrysler service videos on it. It’s very easy to do.

Okay thanks.