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#2551431 - 09/18/18 09:30 AM Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please
SunnyMopar Offline
member

Registered: 10/24/17
Posts: 18
Loc: 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!

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#2551436 - 09/18/18 09:37 AM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar]
Supercuda Offline
I want my mommy!!

Registered: 09/04/07
Posts: 14343
Loc: 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.
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#2551458 - 09/18/18 10:16 AM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar]
krautrock Offline
top fuel

Registered: 01/27/03
Posts: 1796
Loc: 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?

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#2551495 - 09/18/18 11:53 AM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: krautrock]
jcc Offline
No politics

Registered: 12/21/03
Posts: 17384
Loc: Trumussia
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.
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#2551527 - 09/18/18 12:55 PM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar]
RM23U0A Offline
member

Registered: 11/20/11
Posts: 6
Loc: AR
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

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#2551570 - 09/18/18 02:38 PM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar]
Mopar Mitch Offline
super stock

Registered: 01/17/10
Posts: 1073
Loc: 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).
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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!

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#2551573 - 09/18/18 02:45 PM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar]
BigBlockMopar Offline
master

Registered: 01/22/03
Posts: 3437
Loc: The Netherlands
Install an overdrive transmission.
Best of both all worlds.
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#2551574 - 09/18/18 02:49 PM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: BigBlockMopar]
Mopar Mitch Offline
super stock

Registered: 01/17/10
Posts: 1073
Loc: 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!

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#2551576 - 09/18/18 02:54 PM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: RM23U0A]
Pacnorthcuda Offline
I Live Here

Registered: 11/19/07
Posts: 19527
Loc: 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....

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#2551577 - 09/18/18 02:57 PM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar]
BigBlockMopar Offline
master

Registered: 01/22/03
Posts: 3437
Loc: 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.
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#2551610 - 09/18/18 04:34 PM Re: Swap a 3.55 on a rear end 8-3/4 to 2.93 need advice please [Re: SunnyMopar]
BcudaChris Offline
enthusiast

Registered: 03/31/05
Posts: 271
Loc: 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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