4.56 Rear Gears for 2003 H-D

tebraddock

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I am currently researching whether I want to lower my rear-end gears and am looking for info/advice. Have been recommended to go with 4.10s, but like the idea of going to 4.56s. For those of you who have 4.56s, what do you think? For those of you who are just in "the know," tell me what you think based off of these speed to RPM ratios (60/1800, 70/2200, 80/2500, 90/2800, 100/3200). These are obviously cruising numbers.

Here is what I have had done to the truck so far:

MAC Cold Air Intake
MAC Catback
LFP/METCO 2.8" Upper Pulley/6 PSI Lower Pulley/Idler Pulley
DIABLO Flip Chip

This is what is going in/on when the parts come in:

LFP Shift Kit
Bassani 1 5/8" Ceramic Coated Headers
AccuFab Throttle Body
Motive Rear Gears (4.10 or 4.56)

I am also looking at a Mass Air Sensor and a DIS-4, but have currently been advised against either. Any input would be appreciated. Thanks.

Tom Braddock
 

FordSVTFan

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I think 4.56 are way tall! I think your launch will be amazing, but at highway speeds your rear will be screaming.

Have you dynoed with those mods? If so, what are you putting to the wheels?
 

tebraddock

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I have not dyoed yet. I kind of wanted to wait until I had my entire package put together first. However, today I took a guy out who just bought his '03 HD and he wants the same package that I have on his. He baselined over the weekend at 326 to the rearwheels and will go again after the mods are in and get a comparison. I will be happy to post his results after he does that. I am curious myself to see what I'm pushing now, but really want to be awestruck after I get the headers, throttle body and electric fan put on it.

My truck is my main mode of transportation. I have a bike too, but for long interstate trips it will be the truck. Are 4.56s just too much even though I'm running those low RPMs with the 3.73s? And if so, is it even worth the added jump to move up to the 4.10s? I have the 4.10s on order, but would change over to the 4.56s if I can get a couple people that they don't think it would kill the gas mileage or the rear. I know gas will take a hit, but most of my driving is red light to red light anyway. Thanks.

Tom
 

FordSVTFan

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For my purposes I think the 4.56 are too tall for a daily driver. But that is just my opinion.

That friend of yours had a good baseline dyno too.

Let us know how things progress with your truck
 

tebraddock

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Definately going with the 4.10s with the input from yourself and folks that are running 4.10s and love it. Haven't heard anything from anybody running 4.56s. I'm sure that I will be happy with 4.10s. Thanks for your advice. I will be scanning this forum for advice and letting everybody know what I am having luck with and not. Thanks again.

Tom
 

FordSVTFan

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Yah, I would go with the 4.10's. That is a good choice.

Good luck.

Please feel free to post or start a thread here on any topic that applies to the HD 150.
 

SID297

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With 4.56's you would be getting a much smaller pinion gear than stock. You would be putting a lot of power through a fairly small pinion gear. I say go with 4.10 or maybe 4.33.
 

Rainman15

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I just got rid of my 02 SCREW which had 4:56 gears the entire time I owned it. The rpm difference between 4:10 and 4:56 is hardly enough to justify going with the 4:10 because of "driveability" issues. If you aren't making a more significant change from the 3:73 stock gear than that don't even bother wasting the money to change it! I drove my truck to Daytona on the weekend of the 4th and got 15mpg on the hwy @ 70-75 with 4 guys, a cooler full of beer, all our luggage, and a V-Rod in the back, And the truck didn't scream at hwy speeds like they say it will. Also I had my chip burned to compensate for the speedo difference. I had no negative issues at all with that gear selection. It might be a good idea to talk to some people that actually have owned a truck like ours with that gear ratio before you take the word of people that have never even ridden in one.
 

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