Differential Recomendation

[Tonker1]

I have similar set up to you and my car will be a daily driver.
Engine:                        stock 340
Trans:                          TKO 600
1st:                              2.87
5th:                              0.64
Diff:                              8 3/4, 489 case
Ring and pinion gears: 3.23
Rear Tires:                    255/60/15, dia 26.80"

With the current set up, the car would have to going 93mph for the engine to be revving at a comfortable 2400 rpm when in 5th gear. This is a ridiculous set up.

With lower diff gears you'll find the car accelerates a whole world faster and will be a lot more fun. That is why when I've finished spending money getting the car ready for registration I plan on some performance upgrades. One of the best bolt on bang for your buck upgrades is lower diff gears. Currently I'm set on Strange Engineering's 4.10's http://www.summitracing.com/parts/str-rs03-887410l/overview/.

I know you said your car is for street use, but this article by Car Craft has an ET comparison table for various diff gears. The table is worth a look, it's at the very bottom of the article. http://www.carcraft.com/techarticles/ccrp_9812_all_about_axle_gears/viewall.html

[ToxicWolf]

I have similar set up to you and my car will be a daily driver.
Engine:                        stock 340
Trans:                          TKO 600
1st:                              2.87
5th:                              0.64
Diff:                              8 3/4, 489 case
Ring and pinion gears: 3.23
Rear Tires:                    255/60/15, dia 26.80"

With the current set up, the car would have to going 93mph for the engine to be revving at a comfortable 2400 rpm when in 5th gear. This is a ridiculous set up.

With lower diff gears you'll find the car accelerates a whole world faster and will be a lot more fun. That is why when I've finished spending money getting the car ready for registration I plan on some performance upgrades. One of the best bolt on bang for your buck upgrades is lower diff gears. Currently I'm set on Strange Engineering's 4.10's http://www.summitracing.com/parts/str-rs03-887410l/overview/.

I know you said your car is for street use, but this article by Car Craft has an ET comparison table for various diff gears. The table is worth a look, it's at the very bottom of the article. http://www.carcraft.com/techarticles/ccrp_9812_all_about_axle_gears/viewall.html

That's the same tire size I have on mine now.  Good info ... thanks.

[calicuda70]

Here guys Randy's ring and pinion makes 3:73s


http://www.ringpinion.com/b2c/ProductDetails.aspx?ProdID=1793&Product=YG_C8.41-373&Brand=Yukon_Gear_Ring_and_Pinion_Sets&ShowAA=True&Year=1970&Model=Challenger&DriveType=Rear%20Diff%20-%20RWD&DiffId=106&Source=DiffWizard

[joelson6]

just to give you a base line.............

i had 28" tires with 4.10 gears and 1:1 with my 4 speed, 60 mph was 3000 rpm

i switched to 3.73 gears, 3000 rpm was about 65 mph.

i now have 26" tires with the 3.73 gears and i'm back to 60 mph at 3000 rpm.


you should really notice a difference between every gear ratio. each gear should have approximately 5 mph difference,
now factor in the o.d. for your final drive ratio. another thing to remember is with the tall 1st gear and matching that with a
set of 3.73 or 3.91's, you might have a hard time keeping the tires on the pavement. then you'll need to run drag radials
all the time, which isn't all that bad but they do wear fast.

i got my 3.73's (498 case) from summit for around $210

[mr_340]

Dr Diff also carries 3.73's
http://www.doctordiff.com/8-3-4-ring-and-pinion.html

[73EStroker]

I am running a 28" approx tire with 3.73 gears in my Dana. With the Passon hemi OD and 0.8 4th gear I ran about 3000@80mph. Now my new Passon 5 spd has a 0.7 5th gear OD so we wait to skew as I am waiting to drive this thing.

[ShelbyDogg]

I would stick with the 3:23s.  I've had 3:55s behind my OD, then switched to 3:23s behind my 440. It just made it faster and lowered my rpm at my 70 highway cruising speed to about 1900

I my vert, I have 2:76s behind my OD and cruise at 1800 rpm at 70 mph.

Both cars have 295-50-15 tires. Both of mine are fuel injected so they don't "buck" at 1800 rpms.

Were you not happy with the acceleration of your 5sp and 3:23s?

[V02Barracuda]

Dave,

I have the same engine/trans/gears/tire size as you.  The 3.23's just aren't cutting it.  Lugging too much.  I'm switching to 3.91's soon.  With 255/60/15's you'll turn 2307rpm at 70mph. 

3.91's get my vote. 

Good luck.

Mike