3.55 or 3.73 Which Do You Like Better?

[RRcrazy]

1970 Roadrunner 383 .40 over w/ 4 speed. It has the orginal 3.23 gear in it, I want to change to 3.55 or 3.73 dont want to go any further since I will take it on the highway sometimes. I'm looking for more low end performance. The 3.73 calucates to be 3135 rpms @ 70mph, the 3.55 comes in at 2984 @ 70 (this is based on 28 inch tires.

What I want to know since there isnt that big of a difference is your experience with 70 roadrunner with these different gears do you favor one over the other and why.

Thanks

 

[tpodwdog]

i have a 70 RR also....383. i have 3:55 gears in it...automatic. im doing 70 mph@ about 3000 RPM. 55 MPH @ 2200 RPM.

im also running 28 inch diameter tires in back. your speedo pinion will need to be a 33 tooth to be accurate... ( i just spent 4 weeks dialing in my speedo)..i calibrated the speedo with my GPS and its dead on up to 60 mph...it varies a bit after 60. this might save you some time.

i have not had 3:73 's in it so i cant tell you about those, but for highway driving and low end launching on the street, the 3:55's are ideal .

 

[RRcrazy]

So did you have 3.23 and went to a 3.55 was there a big difference. Thanks for the info on the speedo gear. Really looking for better launch.

 

[tpodwdog]

So did you have 3.23 and went to a 3.55 was there a big difference. Thanks for the info on the speedo gear. Really looking for better launch.

no,,,the car came with 3:55's...but i had 3:23's in my old road runner 30 years ago and i remember they were dogs off the line.:blob1:

 

[RRcrazy]

Anybody else have any experience with 3.73 or 3.55 ????

 

[ironherad]

No offense, but a 3:73 ratio was not a stock Mopar gear. Please correct me if I am wrong, but they went right up to 3:91 's (they are great for a big block, but a little deep for a small block) but, what do I know, I run 4:30 gears in my '66 sat...as a driver (just avoid the interstate)...I ran 3:55 in my 68 coronet 383 4 spd car they worked really good! As in, at 70, you can downshift to 3rd and take the headlights right of your victim...

 

[HawkRod]

I have a 73 Road Runner w/ 340 & 727 and a 70 Road Runner w/383 & 4sp. Both have 3.55 sure grips.

I don't have any time behind the wheel of the 70 yet on a highway, but the 73 has a street built 340. It sounds and works really well.

Anyway, I find the 3.55's are a really nice compromise as far as gearing. Still decently quick off the line but not horrible on the highway. I would think with the extra torque in a big block you would be fine with the 3.55 over the 3.91s (or if you have found some aftermarket 3.73).

Just my 2 cents...

 

[zyzzyx]

3.55 or 3.73

I just bought a 3.73 set from Mancini racing for just under $300.00. It's made by Spicer Dana, and it's the whole bearing and shim kit with the new nut. It's for a Dana 60 though. I don't know if that's what you're looking for. The 3.73 is fine for the street, and I would not consider anything in th 4.00 range unless you own a gas station! A little stall convertor in an automatic car with a 3.73 will definitely make you poop your pants!
Good luck.

 

[ilm65]

I originally had 3:73's in my Dana 60 and was running around 3,000 -3,100 rpm at 60-65 mph. It was a little too much for the freeway (had to stay in the right lane) and last year switched to 3:54's--a notable difference. I'm now running around 2,600-2,700 rpm at 65-68 mph and if I "clean it out" up to 70-75 mph, it's still around 3,200-3,300 rpm which is livable. I've got a nice set of 3:73 Dana 60 gears for sale.

 

[RRcrazy]

3.73 gears

No offense, but a 3:73 ratio was not a stock Mopar gear. Please correct me if I am wrong, but they went right up to 3:91 's (they are great for a big block, but a little deep for a small block) but, what do I know, I run 4:30 gears in my '66 sat...as a driver (just avoid the interstate)...I ran 3:55 in my 68 coronet 383 4 spd car they worked really good! As in, at 70, you can downshift to 3rd and take the headlights right of your victim...

Motion and Strange now make 3.73 gears for 489 castings pigs. I am leaning toward 3.73 because 3.55 might not be enough of a difference from my 3.23 that I have now. Dont want to go to 3.91 because I dont own a gas station. Has anybody done a swap from a 3.23 to 3.73 if so what your opinion.

Thanks Guys.

 

[terzmo]

I had 410's with 29 inch tires.....ran around 3000 at 60...was very happy off the line and down the road....355's are more for the highway with 28's as I have them with 26 inch tires on a demon and run around 3000 at 60....when I go back to 28 or 29 inch I will run 391's.....(373's are aftermarket,had them....or they came in a dana and those are not compatable with an 8 3/4) Tire size and gearing are the variables....My friend's pro stock ran around 3000 rpm at 60 but He had 31 inch tires...

 

[RRcrazy]

8 3/4 with casting number 489

I had 410's with 29 inch tires.....ran around 3000 at 60...was very happy off the line and down the road....355's are more for the highway with 28's as I have them with 26 inch tires on a demon and run around 3000 at 60....when I go back to 28 or 29 inch I will run 391's.....(373's are aftermarket,had them....or they came in a dana and those are not compatable with an 8 3/4) Tire size and gearing are the variables....My friend's pro stock ran around 3000 rpm at 60 but He had 31 inch tires...

8 3/4 rearends with pig casting 489 can get 3.73 ring and pinons http://www.drivetrainspecialists.com/categories/chrysler/chry-875-489/products/product-159.html

 

[Lowhound]

Im switching from 4.10s to 3.55s. Havent tried them out yet but the 4.10s were a little to much for highway use. Especially with Flowmasters & 3 inch exhaust. Im tired of getting tickets for loud exhaust. So Im hoping the lower RPMs will make it quiet enough for me to get by.

 

[65 Plymouth Satellite 426]

Just Finished Putting A 8.34-742 Chrysler Case With 3.55 Ring & Pinion, Auburn Posi-Unit and Super Stock Springs Under My 65 Satellite. I Would Say I Prefer That Set Up To A 3.73 For Normal Street Driving. The 3.73 & 3.91 Gears Kept That 727 Feeling Like It Wanted To Shift Again After Getting Into High Gear.

 

[ozonedepletion]

Im switching from 4.10s to 3.55s. Havent tried them out yet but the 4.10s were a little to much for highway use. Especially with Flowmasters & 3 inch exhaust. Im tired of getting tickets for loud exhaust. So Im hoping the lower RPMs will make it quiet enough for me to get by.

I just swapped out from 4.10 to a new 3.55 ring and pinion set from J.Ts.
This is in my 69 bee. I am very happy with the swap as the car feels much better on the highway and at the strip the otherday I still managed 12.4 @111mph. Used heaps less gas getting over to the meet as well.

 

[hunt2elk]

I just swapped out from 4.10 to a new 3.55 ring and pinion set from J.Ts.
This is in my 69 bee. I am very happy with the swap as the car feels much better on the highway and at the strip the otherday I still managed 12.4 @111mph. Used heaps less gas getting over to the meet as well.

What times did you run with the 4.10's before the swap?

 

[383man]

I get the feeling that you will be much happier with the 3.55's. There really wont be much difference in performance and the 3.55's are better for cruising the highway. The 3.73's are great street/strip gears as they give you nice performance and decent cruising rpm's. But if you dont race it much and drive it way more go with the 3.55's. Ron

 

[Inspector71]

This was a help for me too

I have a 68 Charger undergoing a slow (because I'm doing it) but sure (because I don't have the money) restoration. It was a 383 car (auto). It still has the transmission and rear which is a 323 sure grip. I have another 383 block I intend to have stroked (438) and was wondering if the 323 would be "enough" gearing for street and meet driving and an occasional freeway ride. You folks answered my question and I am going with 3.55's.

 

[terzmo]

8 3/4 rearends with pig casting 489 can get 3.73 ring and pinons http://www.drivetrainspecialists.com/categories/chrysler/chry-875-489/products/product-159.html

373 was never offered in a 8 3/4 rearend in the 60's or early 70's

 

[Darter6]

My friend live in southwestern Pa.He and his son are running 3.73 in their cars(B&E body,E body is a stick) both have 451 engines. Good for the hills and twisty turny roads they drive. Now for me I was running 3.55 when I moved out west.(swapped to 2.76)Our roads are mostly open freeways and Loooooong straight roads and the speeds range from 65 to 85-90 (everybody speeds,, you some times have to run above 80 just to keep traffic from running you over). Not sure of where you drive but just a thought.....