3.55 or 3.73 Which Do You Like Better?

[Hemirunner]

Oh that thinking and being stuck in prehistoric times are the other.

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I was at the MATS recently and watched all the NSS cars go slower than my 4200# nitrous street car by over two seconds....lots of purple shaft cams there.... superpro cars were blistering the track with mid 10's. It was embarrassing...

 

[Supershafts]

I have always said there are 2 groups in the mopar camp, the very small group and the overly large popular group... but that large popular group is stuck in the 60's with the performance

 

[terzmo]

tire size (height) and ratio....play with this

http://vexer.com/automotive-tools/speed-rpm-calculator

 

[Bee383]

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

Been reading this old post.i am in the same boat.which gears did you use?happy with them.?

 

[Dennis H]

3:54 Dana. Tremec 5 speed. Perfect combo. Tire smoke galore and 18 plus mpg highway if you try. Loafs at 90.

 

[mont1le]

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.

I went from a 2.76 gear, the improvement was 100% satisfaction light to light but since I Got 3.73 in my DANA 60 with 275-60-15 tires, 727 TQ, I keep wanting to find a 4th gear on the Highway.
An OD would be perfect, need to save $$$$ for that swap.
Going from 3.23 to 3.55 will be about an 8% torque improvement 3.73 will be twice that, being an old post you probably already did the swap, so let us know how it turned out.

 

[Hemirunner]

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...

You won't offend me, but why would it matter if it was never offered as a factory ratio? They never offered jessel shaft rockers either but that won't stop me from using them. I can even hide them under factory valve covers. 3.55's are a great all around gear ratio and the 3.73's are a little better from stop light to light but don't completely kill the highway running like a 3.91 or a 4.10 would. I run 3.73's with a gear vendors OD in mine.

 

[DHD]

I'm setting up my 68 Coronet with 3.73's and an A518 behind the 5.9 Magnum, you can have your cake and eat it too.

 

[RRcrazy]

Been reading this old post.i am in the same boat.which gears did you use?happy with them.?

Some of these old questions keep getting asked....don't they.... Well here is what happened I got a center section with a 3.91 gear just to try it out and it just didn't work for me. Felt like I was driving my John Deere cutting grass. Great Launch and tree pulling torque just felt like I was giving too much top end for street drivng so I had the guy put 3.73 gears in it and I love it. Big difference from the 3.23 it feels like a different car more responsive, great launch, cruises great too. Like I said didnt think going to the 3.55 would make that big of a difference. But remember I have 4 gears. If you have and auto might be best to think about the 3.55 and I'm running 15 inch tires. Hope this helps.., good luck

 

[moparmusclecars]

Ok, now I will ask...How hard is it to change the 3rd member and switch the whole pumpkin on a mopar rear end? DO I just need to pull the axle shafts back and unbolt and replace? I have 391's I want to go to 3:55's

 

[Dako]

Ok, now I will ask...How hard is it to change the 3rd member and switch the whole pumpkin on a mopar rear end? DO I just need to pull the axle shafts back and unbolt and replace? I have 391's I want to go to 3:55's

Pull the axle shafts 'out', so they are not resting on the seals...Then, yes, just unbolt and replace...provided you have an assembled 3rd member ready to go in.

 

[Bigal75]

This kind of thinking is why most Mopars get embarrassed at the dragstrip....and why most aftermarket manufactures won't make any parts for them....

X 4 zillion!!!!

 

[68 Sport Satellite]

I've been wanting to ask this question for some time...I've always heard it's very easy to swap out an 8-3/4 rear end pumpkin to try different gears. Has anyone taken any step by step photos of the process that they'd be willing to post? It does sound easy, but I'm certain there are a few details to worry about that we might be glossing over here -

what about lining up ring and pinion teeth with the axle shafts, grease drainage prior to unbolt, any small parts to worry about flying out when it comes apart, etc? I've never done this procedure before and would like to hear from those who have. I'm considering eventually getting a 2nd assembled 3rd member to swap for track use if it's really that easy. Is it easy to do with jack stands by yourself (bench press the sucker up and bolt it in or use a jack and block of wood to assist)?

Pull the axle shafts 'out', so they are not resting on the seals...Then, yes, just unbolt and replace...provided you have an assembled 3rd member ready to go in.

 

[HYRDGOON]

I've been wanting to ask this question for some time...I've always heard it's very easy to swap out an 8-3/4 rear end pumpkin to try different gears. Has anyone taken any step by step photos of the process that they'd be willing to post? It does sound easy, but I'm certain there are a few details to worry about that we might be glossing over here -

what about lining up ring and pinion teeth with the axle shafts, grease drainage prior to unbolt, any small parts to worry about flying out when it comes apart, etc? I've never done this procedure before and would like to hear from those who have. I'm considering eventually getting a 2nd assembled 3rd member to swap for track use if it's really that easy. Is it easy to do with jack stands by yourself (bench press the sucker up and bolt it in or use a jack and block of wood to assist)?

Grabinov has a detailed and hilarious thread that shows exactly what was needed. He just helped me out a lot in a similar thread and I have a new complete 489 Third Member with 3:55's from Dr. Diff on it's way to me right now.

Here's Grabinov's Link

http://www.forbbodiesonly.com/moparf...ant-me-to-What

 

[Tempest 455]

As I get older, I would rather have highway gears and just more HP!

Seriously though, keep in mind, the more HP/TQ you have, the less gear you need. Such as in drag racing, you gear the car (and tire height) for the MPH it's going to run. You would be shocked how little effective gear ratio some of the really fast nitrous cars run. I digress.

Just keep in mind, small changes in gear you are really not going to be able to tell much difference.

 

[HYRDGOON]

As I get older, I would rather have highway gears and just more HP!

Seriously though, keep in mind, the more HP/TQ you have, the less gear you need. Such as in drag racing, you gear the car (and tire height) for the MPH it's going to run. You would be shocked how little effective gear ratio some of the really fast nitrous cars run. I digress.

Just keep in mind, small changes in gear you are really not going to be able to tell much difference.

That was where my split decision was... I'm installing a Crate Motor with substantially more HP and Torq but I also took into account how I drive the car... I don't spend a lot of time at Highway speeds just a couple trips a year maybe 3 hours round trip so why not get the gear that suits the use of the car as well

 

[Supershafts]

As I get older, I would rather have highway gears and just more HP!

Seriously though, keep in mind, the more HP/TQ you have, the less gear you need. Such as in drag racing, you gear the car (and tire height) for the MPH it's going to run. You would be shocked how little effective gear ratio some of the really fast nitrous cars run. I digress.

Just keep in mind, small changes in gear you are really not going to be able to tell much difference.

You can't use that type of drag racing as the reason for a 600hp car to use a 4.10 in a comparison like that, having 1400 hp in a 4000 lbs car is not ANYTHING the same as a 1400 hp car @ 2600 lbs. You can't use that comparison.

Though 3.55 to 3.73 is not a huge difference and you could get the same effect from a 27" tire to a 29" tire or the opposite way

 

[Tempest 455]

That was an extreme example to make a point.

The more HP/TQ, you make (overall) the less gear you will need. A nitrous motor is an extreme example as in general, makes so much more TQ, will require less gear. Same applies from a 400 HP motor to a 600.

I've played with motors a long time and that's still a pretty standard rule. Of course, lots of additional factors, stroke, smaller ci, max RPM, powerband etc. all will determine final drive ratio needed.

Point was, if he is stepping up the power level, he probably would not need more gear and frankly, probably would not notice a difference.

You can't use that type of drag racing as the reason for a 600hp car to use a 4.10 in a comparison like that, having 1400 hp in a 4000 lbs car is not ANYTHING the same as a 1400 hp car @ 2600 lbs. You can't use that comparison.

Though 3.55 to 3.73 is not a huge difference and you could get the same effect from a 27" tire to a 29" tire or the opposite way

 

[Supershafts]

Yes but again those are examples for the track only. I doubt the op is anywhere near that hp where he can play games with a dead gear and be happy, and would most likely be happier with a 4.10's performance and then need a od gear to complete his full package.
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He needs more gear than the .23 and the .55 isn't going to move worlds, the .73 is better over both.... but again everyone is different