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Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please #2551431
09/18/18 11:30 AM
09/18/18 11:30 AM
Joined: Oct 2017
Posts: 21
Ontario. Canada
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SunnyMopar Offline OP
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SunnyMopar  Offline OP
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Posts: 21
Ontario. Canada
My 3.55 revs at 3200 rpm on the hiway at 60miles an hour what is best gear ratio to change to 3.23 or 2.93 Iam thinking of swapping my 3.55 on an 8-3/4 rear end on a 69 dart, please give your advice if ever done or driven one with 3.23/2.93 rear ratio,
thank you so much!

Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar] #2551436
09/18/18 11:37 AM
09/18/18 11:37 AM
Joined: Sep 2007
Posts: 14,814
up yours
Supercuda Offline
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Supercuda  Offline
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up yours
I'm just curious as to how you came to the decision that this forum was the best place to ask this question. Near as I can figure it has nothing to do with handling.

Maybe you should decide what RPM you want to run at and then do the math to figure which gear would be closest.


They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar] #2551458
09/18/18 12:16 PM
09/18/18 12:16 PM
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Posts: 1,839
central texas
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krautrock Offline
top fuel
krautrock  Offline
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Posts: 1,839
central texas
depends on what kind of driving you do. mostly highway miles, then yeah a 2.93 is great for most people.
more city or slower highway then 3.23 or even the 3.55, there is also some variability based on what rpm's your motor is happy at...

maybe you can put a larger diameter tire on the rear?

Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: krautrock] #2551495
09/18/18 01:53 PM
09/18/18 01:53 PM
Joined: Dec 2003
Posts: 17,655
Trumussia
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jcc Offline
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Assuming you are in the handling section for a reason, that also likely means a shorter tire, then you may actually might as well look for a more common 2.76 ratio and be done with it, you spend a lot more time cruising then accelerating, if you are on the street.


On vacation until 2-15-19 Figuratively
Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar] #2551527
09/18/18 02:55 PM
09/18/18 02:55 PM
Joined: Nov 2011
Posts: 6
AR
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RM23U0A Offline
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RM23U0A  Offline
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Yes, It has been done went from 3.91 to 2.76 on an AAR auto. and 3.23 on another 340 car. The rpm`s dropped to 2600 at 60 with the 2.76. I used a short tire. Drag racing performance changed little; just had to manually shift once in the quarter. Did not need third. Good luck, Wayne

Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar] #2551570
09/18/18 04:38 PM
09/18/18 04:38 PM
Joined: Jan 2010
Posts: 1,090
NW Chicago suburban area
Mopar Mitch Offline
super stock
Mopar Mitch  Offline
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Posts: 1,090
NW Chicago suburban area
I've highway driven with 4.30, 3.91, 3.55, 3.23... and loooong time ago 2.76. The car was typically going to an autocross, or road race track (and occasional car show or cruising).

Currently I'm running the 3.23.. excellent gear for hwy cruising and HHPDE/HSAX and pylon AX... you'll learn the gears (1-2-3, 727) to run whatever event your involved in.

With the 3.23 I can run 1st gear in most pylon autocross events; briefly 2nd, then back to 1st.

With the 3.55 I found it necessary to be 2nd gear more often (slower AX times).

The 3.91 was great; the 4.30 was also great (although too much 1st gear tire spinning and used 2nd more often).

At track lapping events (HPDE/HSAX) the 3.23 is good.. lots of 2nd gear then 3rd gear. The 3.55 needed 3rd gear more often but lost top end mph. The 3.91/4.3 track lapping required 3rd gear dominantly and limited top end mph.

I also have a 2.9 ring/pinion that I'm eventually going to try; I know the 2.9 will reduce the hwy rpms by about 450-500 depending on typical hwy cruising speed (~65-75).

My thoughts with the 2.9 is longer stretches in 2nd and higher mph with 3rd gear... as well as dropping the hwy cruising rpms by 450-500 for long drives (short drives doesn't matter as much).

My engine (340-6) likes to cruise at ~3200-3500 ~65/75.

Look up one the available rpm/mph charts on the web and you can play with that to determine what you'll like. Tire diameters matter; as well as your transmission gears (727 vs stick).


Mopar Mitch "Road racers and autocrossers go in deeper and come out harder!"... and rain never stops us from having fun with our cars... in fact, it makes us better drivers! Check out MOPAR ACTION MAGAZINE, August 2006 issue for feature article and specs on my autocross T/A!
Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar] #2551573
09/18/18 04:45 PM
09/18/18 04:45 PM
Joined: Jan 2003
Posts: 3,481
The Netherlands
BigBlockMopar Offline
master
BigBlockMopar  Offline
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Joined: Jan 2003
Posts: 3,481
The Netherlands
Install an overdrive transmission.
Best of both all worlds.

Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: BigBlockMopar] #2551574
09/18/18 04:49 PM
09/18/18 04:49 PM
Joined: Jan 2010
Posts: 1,090
NW Chicago suburban area
Mopar Mitch Offline
super stock
Mopar Mitch  Offline
super stock

Joined: Jan 2010
Posts: 1,090
NW Chicago suburban area
O/D is the next step... which one... but major $$.


Mopar Mitch "Road racers and autocrossers go in deeper and come out harder!"... and rain never stops us from having fun with our cars... in fact, it makes us better drivers! Check out MOPAR ACTION MAGAZINE, August 2006 issue for feature article and specs on my autocross T/A!
Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: RM23U0A] #2551576
09/18/18 04:54 PM
09/18/18 04:54 PM
Joined: Nov 2007
Posts: 19,702
Kirkland, Washington
Pacnorthcuda Offline
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Pacnorthcuda  Offline
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Posts: 19,702
Kirkland, Washington
Originally Posted By RM23U0A
Yes, It has been done went from 3.91 to 2.76 on an AAR auto. and 3.23 on another 340 car. The rpm`s dropped to 2600 at 60 with the 2.76. I used a short tire. Drag racing performance changed little; just had to manually shift once in the quarter. Did not need third. Good luck, Wayne


I'm having a bit of trouble processing a change from 3.91 to 2.76 having "little" change on drag racing performance.

In fact, I'm having a LOT of trouble with that....

Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar] #2551577
09/18/18 04:57 PM
09/18/18 04:57 PM
Joined: Jan 2003
Posts: 3,481
The Netherlands
BigBlockMopar Offline
master
BigBlockMopar  Offline
master

Joined: Jan 2003
Posts: 3,481
The Netherlands
If you have a smallblock, locating a used A500/518 should cost a few hundred and some fair amount of fab work in an A-body.
You can decide to have it rebuild first or take the chance to install it right away.
I've done it twice without rebuild with success.
Currently fully rebuilding an A500 adn installing a TransGo Repr. kit, but I could have just installed it after a band-adjustment.

Things get more expensive with a bigblock.

Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar] #2551610
09/18/18 06:34 PM
09/18/18 06:34 PM
Joined: Mar 2005
Posts: 326
Colorado front range
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BcudaChris Offline
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BcudaChris  Offline
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Posts: 326
Colorado front range
Since this thread has gone from rear end gearing to OD transmissions, I'll confuse it with a lockup question. For those running A500's, what converter do you run? Do you defeat the lockup? I have an A999 lockup that I intend to put a GV behind once the wallet recovers from the current project.

The best I could find was a tweaked Dakota R/T converter. I've had it flash to 2500 (though my tach accuracy is suspect) but I'd like to be in the 2800 range. I have not been able to find an aftermarket lockup front cover for 904. Anyone know of a 904 lockup front converter cover?


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