stock 3.55 vs 4.56 gears

[BLKDODGE04]

anyone swapped the 3.55 gears with the 4.56 gears? notice much quicker acceleration or change in fuel mileage?

 

[TheSatinPumpkin]

Feels 1000lbs lighter
Went from 3.55 to 4.10 then went to 4.88's and now 4.56's.
Swype-n from my Galaxy Note

 

[Hemi450hp]

Complete night and day difference. Only downside to this swap is if you currently have an open diff with your 3.55's. I would not add 4.56's without some form of limited slip unit out back, so the cost starts to get up there if you need both the LSD and gears.

 

[BLKDODGE04]

what kind of rpm's are u running on the highway at 65 with the 4.56? i have stock 3.55's with 33x12.50 tires and my truck is a **** on the highway, plus it has the 4.7

 

[ralaubach]

^^ been wondering the same thing only for guys that are running a 5.7.

 

[TheSatinPumpkin]

Stick or auto?

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[BLKDODGE04]

auto. i have the 4.7 also

 

[Ramunit]

I went from 3.55's to 4.56's. The truck truly feels 1500lbs lighter. Night and day difference.

The formula is to figure RPM's at a certain speed is gear ratio x speed x 336 divided by tire size x final trans ratio.
4.56 x 70mph x 336 = 107251.2
107251.2 / 33 (tire size) = 3250.03 rpms
3250.03 x .67 (trans ratio in 5th) = 2177.52
2177.52 RPM's at 70 mph in 5th gear.

 

[garner]

Do the 4.56. My buddy did it on his old 4.7 regular cab that he had modded out(ran 14s) and he got better gas mileage with the 4.56 than his factory 3.55 even with his like 31" tires

 

[BLKDODGE04]

someone said something about adding a limited slip setup along with the 4.56 gears. is this necessary or just a good idea while u have it all apart?

 

[garner]

someone said something about adding a limited slip setup along with the 4.56 gears. is this necessary or just a good idea while u have it all apart?

Not necessary but definitely a good idea if your truck didn't come with one from the factory

 

[Hemi450hp]

With 4.56's, you are going to be spinning the "tire" at every stoplight with an open diff. I personalyy would not install 4.56's without a limited slip.

 

[BLKDODGE04]

how can u tell if its a limited slip? ive never really pulled a rear end apart before, i have on a kenworth w900 but not on a pickup

 

[TheSatinPumpkin]

Few ways to check. You the original owner?

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[Hemi450hp]

You can test this the fun way or the boring way.

Fun way - Go do a burnout and see if it leaves 1 tire mark or 2. 1 will mean you have an open diff, and 2 will mean it has a lsd.

Boring way - Jack the rear of the truck up and put it in nuetral. Spin 1 of the tires, and if the other side tire spins the same direction, you have a lsd. If the other tire spins in the opposite direction, then you have an open diff.

 

[BLKDODGE04]

no, ive only had the truck about a year now, it has 170,000 miles on it so who knows whats been done to it. i havent even pulled the diff cover off yet to look

 

[TheSatinPumpkin]

Cool. Post above gave great scenarios to check.

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[BLKDODGE04]

must have an open diff because most of the time if i try to do a burnout its just 1 tire that spins

 

[ramthis9501]

Burnouts are fun lol but I'd do it the boring way to just to make sure... I've seen trucks before with 3.55 open diffs spin both tires in a burnout. Think it's because the motor was producing enough power to do it.

 

[BLKDODGE04]

ive had it break posi once in a burnout. with 33x12.50's tho its kinda hard to even do a burnout period especially with the 4.7 bone stock. its also a quad cab, extra weight doesnt help any