Best Diff Ratio?

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hux340

hux340

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Hi all,
As I live in a semi rural area 50% of my driving is at city limits - 40mph & 50% is highway - 65mph. Based on this what would be a good compromise for diff ratio? I'm guessing 3.25/3.55.
 
Both gears are considered to be good "Driver Performance Gears" with a lot depending on what you want out of your car.

The no brainer is the 3.23's give a slight better mileage and the 3.55's hand out more performance in acceleration. But the enquiring minds need to know what is it YOU need/want out of the car most.

There is a slight rpm difference at cruise between the two gears. You need to find a calculator and realize at what rpm it is that you will be at while in the highway at your realistic hwy. drive speed. From there, you can at least estimate your mileage considering the rpm your traveling at and how much gas it consumes while traveling at speed with a known rpm. Also remember tire size has a play in this as well.

IMO, ether gear is good. I'm running 3.55's now. But I can not give you my mileage yet. Broken speedometer and a still yet to be dialed in carb are a few factors. I can estimate, but I'd rather be accurate in this case now.

FWIW, I do like the 3.55's for performance over the 3.23's that gave up in the rear.
 
Have/ had 3:55 gears,with a 245-60-15 (25 inch diameter) mild 360 ,2800 ger tight converter... Was 2700-2800 @ 60, with @18-20 mpg... Yor really need to add,the whole combination,for actual accuracy....
 
I've got 3.23 in my 71 340 Demon. Great diff gears but wish they were 3.55.
 
Also depends what transmission gear ratios you have, auto or manual, and what size tire you wanna run.. Just don't forget to take that stuff into account.
 
I have now 3.23 gears.
Rest of combo is 318 w 904 trans 2500 stall. Good combination. Higher gears would only make it burn more rubber in my case.
I plan to modify my governor next winter to get better acceleration without loosing nice highway gears.
2700 rpm at 60 mph.
 
50% highway at 65+ mph.. i say 3.23 will make you a lot happier in the long run as long as they will work with your combo...

i was going to put the 3:23 gears i have in the dart when i got a chance but i am really liking the 2:94 gears in the car now..
 
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I have a set of 8-1/4 3.55's out of a Cherokee I regeared awhile back.. if interested I'll part with them for super cheap.
 
This debate has been going on forever . I may be able to shed some light if I may . As was stated earlier both are good . Tire diameter must be taken into consideration . It is much easier to malipulate the tire diameter than the ring and pinion . A 3.55 gear with a tall tire will give the same effect as a 3.25 with a short tire and visa versa . Consider the r.p.m.'s per mile , or kilometer, before you make your decision . Example : I have a 4.10 gear with a 75 series tire that behaves like a 3.55 gear with a 65 series tire . A 1/2 diameter can make a big difference in your enjoyment while driving . Good luck
 
3:23, there has been no mention of "performance" minded driving, so I would go with the percentages and gear it for highway! You won't lose much performance between the 2 going with a 3:23!!
 
Like someone said, also depends on the transmission. As an example, I currently have 3.23s and 25.6" tires and my RPMs are too high, I currently take off in 2nd gear. I'm planning on swapping in 2.76 gears and when I need new rear tires I'll be going with 28" tires or more. Now that all said, I have an ax-15 5 speed out of a 98 Dakota that has a 3.83 first gear so that's the reason I'm needing the gear/tire combo I do. Now I'm sure you're not running a similar trans as I am but there's always that chance so it does make a difference
 
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