Swap 3.23 to 3.55 rear end... Is it worth it?

I could see where 3.23's and 15" tires ain't giving you the low end you'd like. the 904 low gear would be going from a 2.45 to a 2.74 so your first gear overall ratio would be 8.85 (2.74X3.23) as opposed to 7.91 (2.45x3.23) plus I think 2nd gear might be a bit lower with the low gear set also but I ain't sure on that. I would make sure the eng is tuned right including the adv curve with a dual plane intake and the right carb then consider what guys have posted on more in depth changes. If you ain't out on the interstate alot I dont see a problem with 3.91's even. going from a 3.23 to a 3.55 is going to up the RPM's ~10% in all gears and the 904 low gearset is gonna up you ~12% in low gear. Just me I'd go with the low gear set plus a top notch converter if I took the trans out plus 3:55's plus super tune the eng & the components on it

EDIT Along with the low gear/better tc, a 3.73 742 clutch sure grip would be my hands down wish list. I had 4:10's with 14" tires in my first Mopar in 1975, a 440 GTX 4 sp convertible & that was toooo low. The next year I drove it to California & that was back when the speed limit was still 70

Posted By: Supercuda

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 12:44 AM

Quote:

3.91s on a driver is a bad idea. It's even worse if you're used to driving around with 3.23s. You keep waiting for the transmission to shift into a higher gear it doesn't have.

I punted my 4.30s long ago. I hated those things. It made a drag racer very happy that I swapped straight across for his 3.23 set.

I've thought about doing a 3.55 in the Imperial to help it get around town but I will ONLY do that after an overdrive swap.

I disagree, I swapped a set of 4.10's in place of the 3.23's in m 64 300. Then proceeded to drive it from Memphis to Tucson. Never waited for the trans to find another gear it didn't have. Of course it was a three speed stick though so I kinda knew what gear I was in at all times. Nonetheless, the rpm never bothered me. At the time it was the only car I had so it was my DD as well.

Posted By: BigBlockMopar

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 01:08 AM

I agree with Feets here;
If one drives a 'modern' car everyday, once you get into an 'old' car with 3.+ gears, you'll notice the increased (and seemingly unnecessary) higher highway rpm's.
If you're used to a car with 3.23 gears, going to 3.91 gears will indeed feel as if the car is still missing a gear to shift into.

I've pretty much had all available gear-ratios in my Mopars at one time or another, and the 3.23's, a just maybe the 3.55's (in a car with a small engine) is pretty much the highest ratio one can feel 'good' about on highway speeds.

I've been doing some 2.5 hour trips with 3.91 gears a few times with a well built 440 and a 500" stroker under the hood, and I can't say those rides were very enjoyable.

The torqier the engine, the less gear you need in the rear-axle.

Posted By: GY3

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 01:24 AM

A lot of hassle for not much gain (if any).

I had a very similar combo in a 71 Cuda and the the deep 1st gear swap along with all kinds of gears going as deep as 4.56.

In the end I really liked the 3.23 rear gearset and the standard 2.45 first gear in the 904. It was the best of both worlds (drag and street).

As an aside, I built my current '63 Dodge 330 with 3.55's because I knew it would see long runs and lots of street duty. I'd never go deeper than that on a street car with no overdrive. The 440 has more than enough torque so deep gears are not needed..

Posted By: Telvis

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 01:29 AM

Maybe I will just add the 904 lower gearset and keep the 3:23. It will be the lowest cost option for sure

Posted By: rapom

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 02:35 AM

I got the lower 1st. gear set and 2.94's. Love the gear set but sometimes I wish I had overdrive. I can't imagine running 3.23's or 3.55's.

Posted By: 68_661charger

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 02:38 AM

Id say it worth it. I went from 276 to 323 in one Charger long ago and 323 to 355 in another and I thought the 355 switch was more noticeably better but yeah depends on tires and etc etc.

Posted By: Diplomat360

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 03:13 AM

Go for it...

I experienced the following combinations:
1) 2.7x (with low gear ratio 904)
2) 2.94 (with low gear ratio 904)
3) 3.55 (with 727, 2300 stall converter)
4) 3.91 (with 727, 2800 stall converter, but moved to a 4000 Dynamic right now due to the powertrain combo)

A 'day-night' difference between 2 & 3 and again between 3 & 4.

If you can tollerate the higher RPM on the highway (c'mon...not that bad either...) you'll be fine, because when you're in town there just ain't no greater feeling that literally leaving just about anything else behind you...should the need arise...

Now...if you want to cruise as much as you can, and want the motor to just purr along then 3.55 is probably as low as you want to go.

Posted By: dfsmopars

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 03:35 AM

It's difficult for most of us to have it all. I think the 3.23.is a great gear. Right now I have 3.55s behind an OD trans and it is a nice combo for the street. 3.91s are too low without an OD. I've had all of them for the street and if the motor is strong 3.23 sure grip is hard to beat. I've never modded the trans gears but that sounds like a nice option to start with. With a 3.55/904 combo you'll be somewhere around 2700-2800 rpm at 70 mph. My 3.55/A500 combo is 2000-2100 rpm at 70.
BTW my tires are 28.5" tall.

Posted By: Telvis

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 03:45 AM

Quote:

It's difficult for most of us to have it all. I think the 3.23.is a great gear. Right now I have 3.55s behind an OD trans and it is a nice combo for the street. 3.91s are too low without an OD. I've had all of them for the street and if the motor is strong 3.23 sure grip is hard to beat. I've never modded the trans gears but that sounds like a nice option to start with. With a 3.55/904 combo you'll be somewhere around 2700-2800 rpm at 70 mph. My 3.55/A500 combo is 2000-2100 rpm at 70.

I would like to do the A500 if I can find one. I think one of the earlier posters is correct. I will have to tear down a transmission install the gear set and swap transmissions. It wouldn't be that much more of a hassle to just swap for the A500...I started looking for them online. It looks like it might be hard to find a decent one. I need to find a comprehensive list of cars and trucks that had the one I need. I don't want to get something and find it;s the wrong one. I have been reading some of the threads on the conversion. It doesn't look that bad. The solenoids and transmission mount crossmember seem to be the only hard parts. If I can find a decent one I will return the 904 gear set and just swap the transmission.

Posted By: Cab_Burge

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 03:50 AM

If you do the math on the low gear sets, stock and low low gear sets, you sould probally have much more low gear multiplication of torque in 1st gear with the 3.23 and the low gear than with the standard ratio low gear set and the 3.55. My calculator batterys just went tents up just now so I can't , won't, do the math for you. Multiply the low gear ratio times the rear gear ratio to get the starting line ratio

I borrowed the house solar powered calcultor, the 3.23 with a 2.44 low gear ratio, standard 727 gears equals 7.88 in first gear, the same low gear set and the 3.55 rear gears equals 8.66. The low gear set in the 727 is 2.77 if my memory is correct so the 3.23 with them is 8.947 or rounded up is 8.95

The low gear set with the 3.55 would be 9.83

I like using a 1st gear low gear set like that

I use to use them in my 1963 M.W. stocker in NHRA stock class racing

I'm building a new 4 speed street car, it wll have a NP833 O.D stick tranny in it, they come with a 3.09 low gear set with .64 O.D. in overdrive, I'm going to use a set of 3.54 gears in the Dana 60 with a short set of rear tires, hopefully 275x60x15, or what ever will fit in a 1966 Dodge Coronet Deluxe

It pays to think before acting

Especially on car parts and combinations

Posted By: Telvis

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 03:59 AM

Quote:

If you do the math on the low gear sets, stock and low low gear sets, you sould probally have much more low gear multiplication of torque in 1st gear with the 3.23 and the low gear than with the standard ratio low gear set and the 3.55. My calculator batterys just went tents up just now so I can't , won't, do the math for you. Multiply the low gear ratio times the rear gear ratio to get the starting line ratio I borrowed the house solar powered calcultor, the 3.23 with a 2.44 low gear ratio, standard 727 gears equals 7.88 in first gear, the same low gear set and the 3.55 rear gears equals 8.66. The low gear set in the 727 is 2.77 if my memory is correct so the 3.23 with them is 8.947 or rounded up is 8.95 The low gear set with the 3.55 would be 9.83 I like using a 1st gear low gear set like that I use to use them in my 1963 M.W. stocker in NHRA stock class racing I'm building a new 4 speed street car, it wll have a NP833 O.D stick tranny in it, they come with a 3.09 low gear set with .64 O.D. in overdrive, I'm going to use a set of 3.54 gears in the Dana 60 with a short set of rear tires, hopefully 275x60x15, or what ever will fit in a 1966 Dodge Coronet Deluxe It pays to think before acting Especially on car parts and combinations

Great information! It confirms that the lower transmission gear set is definitely the way to go. Now, if I could find an A500 to swap out I could get the lower low gear and an overdrive. I could have the 3:55 or even the 3:91 gears and still have great highway manners. Even if I don't find an A500 I can still swap the 904 gears and keep the 3:23 set I have and do pretty well on takeoff. Those aren't bad options either way. Thanks for the info! I think this is what the guy from Turbo Action was trying to explain. It makes a lot of sense.

Posted By: NachoRT74

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 06:48 AM

Can't talk about maths, but I did it at the same time went with SG replacing open differential and I'm enjoining it without loose on daily driving on streets

Did it with still stock 400 engine and 727 on 255/60-15, now stroked with 175K MP converter and even more fun. I bet with a better TC will be way better, but not funds for that now.

Posted By: Junky

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 07:57 PM

Shorter tire like 26 to 27 inches tall go with 3.23's. Taller tire go with 3.55's. Myself I went from 3.23's to 3.73's with 28" tall tires. I like it. 3,200 RPM down I-5 staying up with most of the traffic. Easy, peesy.

Posted By: Telvis

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/15/14 08:26 PM

Quote:

Shorter tire like 26 to 27 inches tall go with 3.23's. Taller tire go with 3.55's. Myself I went from 3.23's to 3.73's with 28" tall tires. I like it. 3,200 RPM down I-5 staying up with most of the traffic. Easy, peesy.

I'm running 255 60 15 on the rear. I think I am going to either get an A500 and swap or do the lower gears in the 904. If I do the 904 I will keep the 3.23 gears and get a better torque converter. If I do the A500 I will go with a lower gear set, maybe the 3.90 gears. I'm going to see if I can find me an a500 locally. Anyone know how to easily tell the RH from the RE?

Posted By: Darryls-Demon

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/16/14 12:07 AM

I drove my Challenger round trip this year to the MATS from PHX with a 3.55 gear and a 8 inch convertor and after putting over 600 miles on the car that weekend I see no reason in the would to put an OD tranny in the car, it sounds fantastic at 3100 RPMS and 70 MPHs.

Attached picture 8177229-IMG_1273.JPG

Posted By: Magnum

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/16/14 07:25 AM

Quote:

Ever considered going with an overdrive transmission and have best of both worlds?

ANY gear choice will be a compromise in either direction. Another problem with low gear sets in a 3 speed trans. Too much rpm drop at the gear change.

Modern cars have twice as many gears to cover every situation. Launch, high speed cruise and mileage.

Posted By: Paul_Fancsali

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/16/14 10:18 PM

I currently 4.10s in a Duster 340 that engine wants the gear. In my 360 car I run 3.91s now soon to go back to 4.30s or 4.56 gears all you need is a LT tire of about 29-31 tall cuts into gear real fast. The 4.30s were the best all around street gear tall tires cut the revs and the car had a ton of response as far as people passing you wait until you hit a hill. Lesson learned use a quieter muffler As far as gas mileage I get the same with 3.91s as I did with 4.30s. Also my Duster should be getting lousy mileage with 4.10s and 25 tall tires I get 14 around town with a stick

Posted By: gch

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/17/14 01:22 AM

Several years ago I switched from 3.55's to 3.73's in my Polara and I hate it.Too many rpm's at anything above 60 and it just fries the tires at will.I wish I had kept the 3.55's.I have a 3.23 pumpkin that I may swap out.I don't drive mine often or on the highway but I can't even look at the loud pedal without going sideways.Granted mine is torque heavy and if were lacking low end I would probably be more tolerant of lower gears.

Posted By: feets

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/17/14 09:23 PM

Quote:

it sounds fantastic at 3100 RPMS and 70 MPHs.

I would pull my hair out having to listen to an engine at 3100 rpm at 70 mph.

The Imperial runs 3.23 gears and a 29" tire. I plan on slamming an OD in it because I don't like the RPM it pulls on the highway.

Telvis, look in truck and vans for the OD transmission. They're pretty easy to find around here.

Cab, I did the 4.30 gears and 833 OD transmission. That 3.09 first gear was good for a couple car lengths then I had the long drop to the 1.69 second gear. We're talking cruising here, not racing.

Posted By: rtman

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/17/14 10:19 PM

Had 3.55s in my '70 Charger R/T. My conclusion was that the 3.55s weren't particularly good at anything. Didn't give the blistering low-end torque you really crave (like with 3.91s or 4.10s) and weren't as smooth on the highway as 3.23s or 2.76s. I went back to factory 3.23s. The car liked them better (heavy car with AT with stock converter).

For my

, optimal is a low gear and an OD, but that's pricey. I'd swap out the converter before changing the gearing. Good luck.

Posted By: Paul_Fancsali

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/17/14 10:31 PM

Considering how many times you travel the interstate before you decide the gears once a year? Mopar nationals or a show it is not going to kill a good engine to cruise it or to hold 4K. Hell blow out the carbon I know that's what I do before going to track get it on interstate and hold it at 4K Good oil pressure and cooling system and you can drive it on a 90 degree day.I feel if it can't hold it the rev's then its time to rebuild or update.

Posted By: Junky

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/18/14 07:49 PM

Quote:

I would pull my hair out having to listen to an engine at 3100 rpm at 70 mph.

TURN UP THE RADIO. Oops, sorry for yelling. I wanted to make sure ya could hear me over the engine noise.

Posted By: RapidRobert

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/18/14 10:13 PM

Any idea what the dia was on 14" tires on a 68 GTX with stock wheels (magnums?) a rough estimate so I can figure what my RPM was when I went to California in '76 with the 4:10's and the speed limit was still 70MPH? iirc they were F70-14

Posted By: Twostick

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/19/14 12:35 AM

Quote:

Any idea what the dia was on 14" tires on a 68 GTX with stock wheels (magnums?) a rough estimate so I can figure what my RPM was when I went to California in '76 with the 4:10's and the speed limit was still 70MPH? iirc they were F70-14

I'm guessing there were more numbers to the left of the tach needle that you didn't have than to the right.

Kevin

Posted By: RapidRobert

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/19/14 12:39 AM

I was my first Mopar which hooked me. I was 25 & it was buzzin

Posted By: Telvis

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/19/14 01:06 AM

The 4:10s would probably be a little higher RPM than I would feel comfortable with. I think I'm going to put the lower gear set in my spare 904 and get a better converter. Then if I need more gear than the 3:23 set I might swap to the 3.55. The overdrive would be nice but I don't feel like fabricating a mount and all the other issues with fitting everything in the car. I wold rather rebuild the spare 904 and install the gear set then just slip everything in place. Easy peasy and no headache. I'm tired of headaches...

Posted By: Twostick

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/19/14 06:14 AM

Quote:

I was my first Mopar which hooked me. I was 25 & it was buzzin

F70x14 is 26.2ish" with 4.10's calcs out to 3700 at 70.3 MPH.

Did it have glass packs too?

Kevin

Posted By: Twostick

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/19/14 06:23 AM

Quote:

The 4:10s would probably be a little higher RPM than I would feel comfortable with. I think I'm going to put the lower gear set in my spare 904 and get a better converter. Then if I need more gear than the 3:23 set I might swap to the 3.55. The overdrive would be nice but I don't feel like fabricating a mount and all the other issues with fitting everything in the car. I wold rather rebuild the spare 904 and install the gear set then just slip everything in place. Easy peasy and no headache. I'm tired of headaches...

If you have the "Right" converter then the "wrong" rear gear is not as big deal unless you are chasing the last tenth.

One of the mags did a comparison years ago between an optimized engine and converter package and rear gears from IIRC 2.76 to at least 4.10.

There was only a tenth or two between them all and they all MPH'd within a couple also.

Kevin

Posted By: Sport440

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/19/14 06:25 AM

Tevis, 3.55,s or a good vert in your case. Get out there and test your current TCI and see where it stalls at.

As you stated, even you dont know. Do it and report back. If it ends up being around 2400, get a tight 4200 + stall vert and keep your 3.23,s. or keep you TCI and go with the 3.55,s.

Change to the low gear set later, on your 904 rebuild when your ready, as a additional upgrade if needed.

Posted By: cudaman1969

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/19/14 11:32 PM

Two gear sets... 2.76 street ... 3.91 street-strip with short tires and quite mufflers.

Posted By: HotRodDave

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/19/14 11:51 PM

Quote:

Two gear sets... 2.76 street ... 3.91 street-strip with short tires and quite mufflers.

Or put in an a-500 and 3.91 and have the same effect at the push of a button

Posted By: scratchnfotraction

Re: Swap 3.23 to 3.55 rear end... Is it worth it? - 06/20/14 12:12 AM

Quote:

Shorter tire like 26 to 27 inches tall go with 3.23's. Taller tire go with 3.55's. Myself I went from 3.23's to 3.73's with 28" tall tires. I like it. 3,200 RPM down I-5 staying up with most of the traffic. Easy, peesy.

whiplash effect x2

3,200 and Buzzz awhile.

Swap 3.23 to 3.55 rear end... Is it worth it?