Gear Swap time 4.10's or 4.56's?

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I've been stuck with 3.55's for almost 2 years now in my 10' RCSB 4x4
and the time has finally come to upgrade!

I've been running 28" M/T DR's on 17" wheels at the track to drop my effective gear ratio to around 4.30:1
The 295/45R17 Mickey Thompson ET's (x4 for my 4x4) shaved 5 tenths off my quarter, and got me into the 13's (13.8/98.5)
...along with the basic intake/exhaust/tune mod's everybody runs.

Most recently I stepped up to an Edge Torque Converter that stalls at about 3000 rpm,
and dropped another 3 tenths off my 60' down from 2.1's to 1.8's but traction is dependant on perfect conditions/prep now.
My new headers just arrived this week (JBA coated shorties)
and before I go much further adding power it's time to address my traction issues due to my open rear diff and 3.55's
I'm getting to the point that I often need to use an AWD (4WD Auto mode) and 4 drag radials for traction.

Since a Locker will keep me from doing a 1 wheel peel,
I may as well upgrade my gears when the rear carrier comes out in favour of a Detroit Tru-Trac limited slip.
I've been doing some calculation,
and I "think" ideally I should be aiming for about 5800 RPM at the finish line in a 1:1 3rd gear. Right?
I'm currently running a Diablo 93 tune, shift points are maxed out 6200-6400.

So what do you think? 4.56's too low? are 4.10's a better choice?
For daily driving I roll heavy 305/50R20 Terra Grappler's on stock 20's
90% city commuting and very rarely see any highway time.
I've recently found some good on-line calculators here...
Not sure what number to use for torque converter slip so I just used 10%

Here's where I'm at currently with 3.55's on my 28" tires:
3rd gear is falling on its face at 4600 rpm at the traps

with 4.10's put me at 5300, much closer to being in the powerband at the traps

and 4.56's put me right on the edge before 4th gear kicks in after crossing the 1320' mark

Anybody here running lower gears for racing confirm those numbers?
That last thing I want to do is end up shifting into 4th (overdrive)because I've gone too low with 4.56's.
I have to regear both front and rear diffs,so I need to get it right the first time.
I suppose if I end up with too short a gear,
to correct it I could just get new taller tire 30"-31" tires and sell the 28's.

FWIW, my best times at the track on my heavy Grapplers/20's are 14.4's with 3.55's
I bet I could get high 13's on them on 4.56's and my new headers :D
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Discussion Starter · #5 · (Edited)
My street tires are 305/50R20 Terra Grapplers
they are 12.2" wide by 32.2" high and on mystock 20's weigh in at over 90lbs ea.

I currently run 14.4's on them at the track
..and thats at 2500'+ DA, would be high 13's at sea level.

I'll probably turn them at 2300+ rpm on the highway with 4.56's, but that wouldn't be very often.
My truck is primarily my city commuter/weekend warrior and wont see 5th gear very often.

I run a 93 octane tune all year round, never less than 94 octane fuel,
my throttle boost and shift points on my Diablo Trinity are maxed out.

Fuel economy has never been a concern, go fast or go home.

Although I've never re-geared a truck for the track,
I have done many Jeeps with 4.56's and ARB air lockers front and rear,
so I do know and appreciate the performance benefits of a gear swap.

I was a Jeep Jamboree Trailguide for almost 10 years
my last ride....built by myslef from the ground up except for the axles, I leave that to the pro's


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Discussion Starter · #8 · (Edited)
This is why I'm asking for "Real" results from someone that's done it rather than guessing or relying on calculators.

I've read that a gear reduction only effects your ET,
and traps speeds remain aproximately the same if all other parameters remain equal.

With the limited experience I have, I believe that to be true.

I also believe that regardless of power adders or internal upgrades, like cam/heads,
RPM at the finish line will remain constant with tire size x gear ratio x trans gear ratio.

I have a bud with an SRT10 Ram who runs 4.56's and M&H 390/40R17 DR's (29" Tall) and a 100 shot
so there's no way I'm going to run more power than him, so I cant understand how 4.56's could be "too much" gear for my Ram with substantially less power.

As I said before, should it be too low, although I cant imagine it
an easy fix is to just go to a taller drag radial, right?

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Discussion Starter · #12 · (Edited)
That's exactly why I made a point of saying this is not a highway truck that will be spinning 2300 RPM in 5th gear at 70 mph for hours on end..

I only use the truck occasionally to-from work and it wont likely ever even get to 5th gear.
Getting from intersection to intersection in the city is a lot shorter than a quarter mile.
Performance>Economy are my priorities and I cant imagine why 4.10's that are barely better than 3.92's would be the best choice.

Gas milage would be the only down fall if I was spending the majority of my time at highway speeds.

My Ram is two years old and has about 12k miles on it, it is not my only vehicle.

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Discussion Starter · #16 · (Edited)
It sounds like you have talked yourself into 4.56 though.
What I'm asking for, in the "Drag Racing" section,
is performance experience/opinions from those who HAVE raced with 4.56's.
...not what gear would be more streetable. :doh:

chefred, kay-9, Randtx ? are you guys around still?
or is my question is better suited to hardcore racers at NADodge.

Yes I want to run 4.56's, why? I've done it before on other vehicles I've owned,
and because there are already many Ram's running 3.92's,
So are 4.10's going to be a significant advantage over them?, for $3000+? Hell no!

If I'm going to "upgrade", I want to pick up as much RPM as possible for the $ without going over right?, if 5900 rpm costs the same as 5300rpm, why would I waste my time and money by settling for less?

I could have upgraded my torque converter from 2300 to a stock R/T 2600
but chose to go one step further for a reason, and now I can bury them off the line with a 2800-3000 stall.

Why not do the same when it comes to re-gearing???

[edit note]...just for the record, I have only 12k miles on my 2 y/o Ram
and have 3 other vehicles to drive, all for different needs/requirements.

only requirement for this truck is to be FAST, all the time!
I run a performance tune and 94 octane all year round, 4WD in the Winter
and drive the hell out of it always...lucky to see 10MPG and I dont care :p

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Discussion Starter · #18 · (Edited)

final drive ratio is the same ? no difference on the track?

I already have the 28" tires, def not going smaller
so the only factor is the gearing, and I NEED a locker

4.10's = 5300 rpm at the traps
4.56' = 5900 rpm at the traps

do you not comprehend that?

my city commute is from stop light to stop light
that's actually LESS than a quarter mile.

so how is a lower gear that's better for the track, less streetable?

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Discussion Starter · #20 · (Edited)

I didnt start this thread asking what tire size I should run, I'm under-geared with open diffs.
I need a rear locker to help avoid a one-tire-fire, and want to take the carrier swap opertunity to change gears at the same time.

I purposely bought a set of (4) light weight 295/45R17 DR's to drop my effective gear ratio from 3.55:1 to ~4.30:1 two years ago.

With my Drop, if I go any lower on my tire height I'm going to bottom out :D

I want to drop my 13.8 to mid 13's, on my DR's
and I want to be able to run my 20's occasionally and go from 14.4's to high 13's
I would like to be able to do it in 2WD whenever possible, which inst likely with an open diff now that I have a higher stall TC.

My heavy 305/50R20 Grapplers best time on 3.55's is 14.4 but traction with open rear diff is hit and miss... all terrain tires suck for traction in 1 wheel drive

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Discussion Starter · #22 · (Edited)
28" is about as small as I care to go, and buying lower tires instead of lower gears still doesn't address my open rear diff ;)

My bad for not spelling it out clearly enough in my opening post,
allow me to simplify things...

Has anyone ran a 4.56 geared Ram at the track on 28" tires
and have you managed to avoid hitting 4th (over drive) gear before the end of the quarter mile?

or Has anyone ran 4.10's and thought they could use a little more gear to get the rev's up an extra 500-600 rpm?
From Drag Race forums I've been on it would seem you want to be at your max RPM at the line.

My best guess is the RPM would be 5900 RPM, in 3rd (1:1) with 4.56's and 28" tires, is that close?

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Discussion Starter · #27 · (Edited)
you know me..i am a staunch 4.56 guy...I still trapped 113 mph with 28" tall dr's in 3rd gear...but, with that said, for you I'm leanin towards 4.10's because your a regular cab and have the 3k stall...

also, with the gearing and tires i run, i hafta to shift to 2nd at 5k rpms to hold 3rd thru the traps..
Thanks Fred, without spray, I'm not going to be anywhere near 113mph

Yes a Reg Cab, but being a 4x4, it weighs as much as a 2wd QC
and has a little more rolling drive train resistance due to the front diff and CV shafts always turning, powered or not
and I have a transfer case that could be turning two drive shafts when traction is poor and I use awd.

I was mostly concerned about staying in 3rd at around 99 mph. 4.10's would be the safe bet, 4.56's sounds right on the border.

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Discussion Starter · #30 · (Edited)
Thanks Fred! you're too kind

That's very helpful info

I'm going to see if I can downshift after 3rd at WOT
My only concern is the downshift will go to 2nd prime, not to 2nd.
it sounds like it may just be a matter of getting the timing right and doing it very shortly after hitting 3rd.

... I can always adjust shift points with my Diablo too.

The 4G's don't have a "D" when you switch to manual (ERS) mode
just 1-2-2p-3-4.

on my larger street tires/3.55's
I can almost get to the line in 2pr in manual's just shifting to 3rd at the line.

if I just use D, it goes 1-2-3 with 3rd gear coming well before the traps.

The benefit on the street with 4.56's appeals to me too,
my heavy ass grappler's on 20's need all the help they can get.

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Discussion Starter · #33 · (Edited)
4.56 might be cutting it too close, (4th gear at the 1320')
if there was a 4.30:1 option in between for a Dodge it would sure make things easier

As you can probably tell, I'm doing all I can to try and make 4.56's work
Part of its for a mid 13 pass at the track on DR's But....

I still want to be able to get a 13.9 pass with street tires too
for when I feel too lazy to do a 4 wheels swap to my DR's.
(Hey, I'm gettin' old and it happens)

Best runs so far on my 305/50R20 Terra Grapplers is 14.4's
I'm kind of hoping 3.55's to 4.56's will shave 4-5 tenths

I know 4.10's would come up short.

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Discussion Starter · #35 ·
Okay, I'm Sold ! 4.56's :smiley_thumbs_up:
You make it sound like Way too much fun to resist.

Good to hear it from someone who's been, there done that.
When the track re-opens for the season (1 more month to go)
I'll try some different shift combo's with my DR's/3.55's.

If it's too much gear and I can't shift it to hold 3rd to the line,
I guess my next move could be a slightly taller DR ;)

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Discussion Starter · #39 ·
Ouch! hope that turns around for you in better air,
but that's a lot of tenths to make up. Crap, I feel for you man.

What are your shift points at?

I just got my Headers on last weekend, and I'm booked for a custom dyno tune on the 14th.

I'll see what my CMR has to say,
and will track test my new setup on the 27th before making a major commitment on gears now.

I'm not rushing into this, it aint cheap to do both diffs on a 4x4
and I may wait unitl mid summer to do it when its too hot to race.

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Discussion Starter · #43 ·
High DA is one thing, but if it fell on its face going into overdrive before the traps, that's going to hurt you every time.

Run it a couple more times,
1) try using 2nd prime (manual shifting)
2)see if you can borrow a taller DR from someone
3) take note of what gear/rpm your at when your approaching the finish line each time.

I think a 4.30:1 would be the answer, but that isn't going to happen unfortunately
So you may have to go 4.10's or change tires to a 30".

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Discussion Starter · #49 · (Edited)
4.30 would be a no-brainer, but that's not an option for a Chrysler 9.25 diff.
It all comes down to the number of teeth on the pinion in relation to the number of teeth on the ring gear.

as a result I'm afraid I'm faced with settling for 4.10's
or going to 4.56's and needing to buy 4 new DR's that sit about 29"-30" tall.

The key is definitely to stay out of 4th gear before hitting the traps.

I cant do any track testing or detailed calculations until I get back to the track,
I need to know my exact RPM's at the line but our track doesn't open until April 27th.

My effective gear ratio with 3.55's and 27" DR's is about 4.30:1
I believe I'm 4400-4600 rpm in 3rd gear, but not 100% sure.
If I can get to 5800 in 3rd with 4.56's and my current tires, that will be the determining factor.

If I'm wrong and I shift into 4th. I'll be in overdrive at 3000 rpm at the traps, and have to shop for new tires.

I may scrap the entire gear swap and just add a rear LSD, then spray it :D
Why struggle for mid/low 13's when I can get 12's for less $$$.


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Discussion Starter · #53 · (Edited)
Good deal,
I remember looking into that 4.10 rear diff shortly after getting my Truck,
unfortunately the shipping to Canada would negate any savings,
and I've still got a front diff I'd have to match.

I'm looking at $1800 parts (Gears,Locker, bearings etc.) Front and Rear
and about $1500 in labor :158:

Diablo Tuners use Chip Master Revolution software (CMR)


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Discussion Starter · #56 · (Edited)
Does that include the LSD as well or is that just the gears, I'm a slight newb to this whole rear diff thing, I want to swap out the 3.55's for the 4.10's with a limited slip so I'm not peg legging it anymore.

It's the entire R/T rear axle assembly, all ready to bolt in
Housing, Gears, LSD Carrier, Axle Shafts already assembled.

I think all you do is swap your own brakes over.

third selection on this page...

The axle change is a pretty easy for the average shade tree mechanic to swap, just a driveshaft, control arms, track bar, brake lines.
installing and setting up a ring/pinon takes a skilled tech that can charge you more in labor than the price of the gears/carrier/install kit and bearings alone.

If your 3.55 rear axle is still fairly new, you can sell it to recoup some of your cost,

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Discussion Starter · #61 · (Edited)
Oh yea haha shipping plus labor would kill you. Didnt take that into consideration. Since the mopar dealership is here I can just pick it up an do the install myself when i get around to getting myself the 4.10's.

Wow i was never introduced to this before. Am i seeing this right. 2500$? Or does the performance shop your going to already have this? That is pretty cool. I didnt know of this program.
Oh I could swap the entire axle over myself,shipping it here would be +$500 though, but that's just the Rear
There is no such thing as a Mopar Front 4.10 axle for a 1500 Ram. So I would still have to buy aftermarket, and pay someone to swap the R&P up front for my 4x4.

I'm going to bite the bullet and go with 4.56's and a True Trac... Go Big or Go Home!
No use going half assed now, I want to be a street killer too, not just at the track. :D
Need to make a few passes with my new headers first though, will look into the gear swap mid summer when its too hot for racing.
Then I'll be back to the track in fall to destroy the competition.
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