3.55 or 3.73 gears in 66 dart gt

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maldridgeks

maldridgeks

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Hello everyone,

I'm looking to bump up the torque in my 66 dart gt. Car has 273 with 4 barrel carb, 3 speed 904, and 8 3/4 sure grip with 2.93 gears now. I understand my dart could have come with up to 3.55 gears from factory. Anyone have experience with 3.55 and / or 3.73 gears in similar setup? Main use of car is cruising around town and of course occasional burnouts and such. No aspirations for track. Only occasional highway.

Thank you.
 
IMHO

I have 3:23 in my 67 dart. Highway is no issue.

3:55 is a nice compromise.

My friend has 3:73 in his 67 dart. And he has to lead on the interstate as he is screaming at 75mph.

From an online calculator.

26" tires 75mph (add trans slippage and the numbers are higher)
2.93 = 2840
3:23 = 3131
3:55 = 3441
3:73 = 3615
 
66 Barracuda with 24.5” tall tires.
8-3/4 rear with 3:23 sg. Highway is will cruise all day at 75mph
Back roads and take off a tad slow but the 273 makes power more up top then down below. (Old adage is still true. “You cannot beat displacement.”)
To jump from a 2:9 to 3:23 not worth it.
3:55 is worth the jump but top
End will be lost “some.” I like not screaming at 70. But I do dream of Smokey burnouts.
Lol! How tall of tire do you have in the rear?
Syleng1
 
I went from 2.93 to 3.55s when I put the 8-3/4 in my 65. Thought I would be happy with it. (273-4 4bbl 4 spd). On the highway I wasn't happy with it. Put a 1000 miles on its first trip out after the swap. Noticed I was in the 4 bbl a lot at the 80mph zones.

After a couple years, I switched to 3.23s and am much happier with the ability to be on the highway and not be rev'd as high.
 
if you don't care about highway 3.73 then, I'd go 3.91 get a full ratio over the 2.93
 
I run 3:91’s with a 4 speed. Has been a 273-4bbl, 340 and now a Gen 3 Hemi. Great fun around town
 
maldridgeks said:
Hello everyone,

I'm looking to bump up the torque in my 66 dart gt.
Click to expand...
It's not really about bumping up tq, it's about getting into main powerband easier say 3500-5500 rpm, 2.93 takes about 38 mph in 1st just to get to 3500 rpm, 3.91 gets there at 28 mph a more reasonable speed, to just enter the powerband.
 
Gear ratio is about torque multiplication. That’s why 2.76 kills it so bad and 3.55 is what everyone wants.
 
I have 3.23s behind a warm slant 6 and it's plenty snappy. 3.55 is too much for highway cruising, really.
 
Well, in the OP's case, since he uses it mainly for around town and only occasionally highway, I'd go 3.55, maybe 3.73 if it really only occasionally gets highway use. Either would be a lot peppier than the 2.93 gears he has now.

Agree with everyone who says 3.55 is really too low (high numerically) for sustained highway cruising. Although, back in the day, a friend of mine had a GTO with 3.90 gears and he routinely cruised at 90. Don't know how long his motor lasted, though, as he left school and I never saw him again.
 
maldridgeks said:
Hello everyone,

I'm looking to bump up the torque in my 66 dart gt. Car has 273 with 4 barrel carb, 3 speed 904, and 8 3/4 sure grip with 2.93 gears now. I understand my dart could have come with up to 3.55 gears from factory. Anyone have experience with 3.55 and / or 3.73 gears in similar setup? Main use of car is cruising around town and of course occasional burnouts and such. No aspirations for track. Only occasional highway.

Thank you.
Click to expand...
3.55 is exactly what you are looking for
 
65 Cuda 340 said:
Don't know how long his motor lasted, though, as he left school and I never saw him again
Click to expand...
He is still standing on the side of the highway waiting for you to come pick him up!

Screenshot_20230911-152934.png
 
Dana67Dart said:
IMHO

I have 3:23 in my 67 dart. Highway is no issue.

3:55 is a nice compromise.

My friend has 3:73 in his 67 dart. And he has to lead on the interstate as he is screaming at 75mph.

From an online calculator.

26" tires 75mph (add trans slippage and the numbers are higher)
2.93 = 2840
3:23 = 3131
3:55 = 3441
3:73 = 3615
Click to expand...
Thank you very much
 
Syleng1 said:
66 Barracuda with 24.5” tall tires.
8-3/4 rear with 3:23 sg. Highway is will cruise all day at 75mph
Back roads and take off a tad slow but the 273 makes power more up top then down below. (Old adage is still true. “You cannot beat displacement.”)
To jump from a 2:9 to 3:23 not worth it.
3:55 is worth the jump but top
End will be lost “some.” I like not screaming at 70. But I do dream of Smokey burnouts.
Lol! How tall of tire do you have in the rear?
Syleng1
Click to expand...
Thank you again.

On rear of car I'm running 225/70 r14's - they are rated to be 26.4" tall.
 
413 said:
Gear ratio is about torque multiplication. That’s why 2.76 kills it so bad and 3.55 is what everyone wants.
Click to expand...
The goal of more tq doesn't help figure out optimal gearing, for pure acceleration a continuous variable tranny that kept you at peak hp would be ultimate solution, best we can do is best average, for the OP being able to get into the main powerband at average intown road speeds would be my goal.

2.93 26" 1st gear 3500 rpm @ 38 mph, 2nd gear 5500 rpm @ 100 mph
3.23 26" 1st gear 3500 rpm @ 34 mph, 2nd gear 5500 rpm @ 91 mph
3.55 26" 1st gear 3500 rpm @ 31 mph, 2nd gear 5500 rpm @ 83 mph
3.73 26" 1st gear 3500 rpm @ 30 mph, 2nd gear 5500 rpm @ 79 mph
3.91 26" 1st gear 3500 rpm @ 28 mph, 2nd gear 5500 rpm @ 75 mph
4.10 26" 1st gear 3500 rpm @ 27 mph, 2nd gear 5500 rpm @ 72 mph

Here's a dyno of a 273 commando

1694558580227.png
 
Last edited:
The rear end ratio is always a trade off. If you want quicker acceleration, get lower gears. If you want mileage with lower RPM on the engine, get higher gears. I wouldn't go lower than 3.55's in your case if you do any freeway driving. 3.23's would probably be your best choice with an automatic, but, if you don't mind the extra fuel being used, extra wear on the engine, extra exhaust noise, and potentially less traction, get the 3.55's or 3.73's. It mainly depends on what you want the most.
 
Another thing you could do is more stall so to start in/nearer to the main powerband, go with lower 1st & 2nd gears 2.74/1.54 vs 2.45/1.45, or swap in a OD tranny get all that.

I'm sure these are more than you want do, but if you got the cash and desire it will get the most out of the 273.
 
yup...install the lo set 1st and 2nd gears from a later transmission.
Torque multiplication will be like using 3.30:1 rear gears in first and a little less in second and your final drive
ratio will remain 2.94.
That extra rpm from a 3.55 or 3.91 lo gear set is not just the rear gears. It spins everything faster...crankshaft, camshaft, distributor, waterpump, fan, alternator, fuel pump, power steering pump, transmission and torque converter, driveshaft and both u joints, and gears. and they just create a ton of vehicle harmonics. Another option would be a
modern tight torque converter wit a higher flash stall.
 
maldridgeks said:
Hello everyone,

I'm looking to bump up the torque in my 66 dart gt. Car has 273 with 4 barrel carb, 3 speed 904, and 8 3/4 sure grip with 2.93 gears now. I understand my dart could have come with up to 3.55 gears from factory. Anyone have experience with 3.55 and / or 3.73 gears in similar setup? Main use of car is cruising around town and of course occasional burnouts and such. No aspirations for track. Only occasional highway.

Thank you.
Click to expand...
I put 3.73s iny 65 Signet. Was 2 Barrell now a Commando look. Have 225x70 radials. Built rear when planning on mild 340. Sold engine. I would like better if had 3.55s. Good compromise.Quick acceleration but better road gears
 
my vote goes for 3.55's

to me that's the compromise on what you're looking for. perfect for around town cruising and the occasional smoke show when called upon, totally acceptable for some occasional highway use.
 
And if you run 3.23:1 rear gears first gear will be the equivilant of 3.60:1 and with the later lo gear set.
 
65 Cuda 340 said:
Well, in the OP's case, since he uses it mainly for around town and only occasionally highway, I'd go 3.55, maybe 3.73 if it really only occasionally gets highway use. Either would be a lot peppier than the 2.93 gears he has now.

Agree with everyone who says 3.55 is really too low (high numerically) for sustained highway cruising. Although, back in the day, a friend of mine had a GTO with 3.90 gears and he routinely cruised at 90. Don't know how long his motor lasted, though, as he left school and I never saw him again.
Click to expand...

We were much younger and dumber then!
 
maldridgeks said:
Hello everyone,

I'm looking to bump up the torque in my 66 dart gt. Car has 273 with 4 barrel carb, 3 speed 904, and 8 3/4 sure grip with 2.93 gears now. I understand my dart could have come with up to 3.55 gears from factory. Anyone have experience with 3.55 and / or 3.73 gears in similar setup? Main use of car is cruising around town and of course occasional burnouts and such. No aspirations for track. Only occasional highway.

Thank you.
Click to expand...
I have a 66 Dart Conv. with a 318 & 904 I had 3.55 gears and felt I needed another gear so I swapped in a set of 3.23's and now it cruises nice
Joe
 
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