[mmmhoss]

I have a 2002 1500 short bed, automatic transmission, V6 3.7L engine with Regular Cab. It is stock in every way. 17" wheels.

It came with 3:55 gears.

It seems that most responses on the forum say to put 4:56 gears for better fuel milage and power.

When I called my mechanic to see what he would charge, he said about $400 labor. I bring the gears.

He also told me that the guys running the 4:56 gears probably had big tires and wheels, as well as standard transmissions.

He said with my setup, I would be running about 3500 rpms at 65 mph.

My mechanic states that he would not go any lower geared than 3:?? gears. I can't remember what he said, but it was lower than 3:55 but was not in the 4:XX range yet.

So my question is, has anybody put the 4:56 gears in a truck like mine? Was it a good thing for the fuel milage?

 

[HemiDak]

Most of the guys with 4.56's are running automatics. I would say that a good portion of them are both stock and larger tires.

As far as what RPM you'll be running, give me your tire size and I can calculate it out for you at any given speed.

 

[VengefulHemi]

i have 33x12.50 toyo mt's and i'm looking into 4:56's. what rev's could i expect. thanks man.

 

[ce2flaco]

http://www.dirtroadmagazine.com/gears.htm

http://www.differentials.com/calc.html

http://www.tyres1.com/calculators.html

http://www.bncoffroad.com/tire_gear_cal.html

http://www.4lo.com/calc/gearratio.htm

http://www.rocky-road.com/calculator.html

http://www.dakota-truck.net/TIRECALC/tirecalc.html

There are a zillion of these floating around the web. Pick one and have at it.

 

[schawks73]

If you are sticking with your 17's and not going with a bigger tire, i would think that 4.10's might be a better fit for you... crusing at 2krpms at 60, and its a 200rpm swing in either direction every 5mph (ex. 65 = 2200, 55 = 1800, etc)

This is on my 4.7L QC using the stock 17's.

other than reving at high rpm's... 4.56's were "Very NIIIICE" (Borat)

-David

 

[Josh Brown]

Find a new mechanic he doesn't know what he is talking about if you have the 5spd auto. I would guess that rpm if OD was off.

 

[DylanL]

For mileage alone with stock tires (245/70/17) you would need to go the other way in gears and drive ALOT on the highway. W/3.55 gears @ 70 MPH and stock size tires (30.5 inch dia.) thats around 1916 RPM with an Auto w/OD (depending on the OD ratio). It would run about 2462 RPM with 4.56 gears, all else being the same....... that will make a significant DROP in mileage.

Ain't no free lunch, more power = less fuel mileage (unless your in a diesel)

 

[dale3fan3]

Does the 6 cyl have the 5 spd tranny? I thought it was 4 spd. I know kruser79 had the 4.56 put in his 4.7 and his rpms were high with the 4 spd auto. HE needed to get them down a little so he swapped the rears only to a 285 tire.

 

[GrimReaper]

i can seee this mechanic saying "i told ya they would break" or something to that nature if his instal goes bad....

 

[mmmhoss]

It is a 4 speed automatic. 3 speeds and a overdrive.

 

[JeffB2002]

With the 4 spd....I have one as well.....The 4.56's will be a little much on RPM's....BUT you also have to remember you have a V6 and not a V8. The lower amount of HP that your engine has will increase the RPM's at the same speed as the V8. I know that Craig has 4.10's in his truck and his RPM's are lower than mine. Why? Because he has a Hemi plus a 5 speed. For your V6 I would not go any higher than 3.92 or even 4.10.

 

[schawks73]

For mileage alone with stock tires (245/70/17) you would need to go the other way in gears and drive ALOT on the highway. W/3.55 gears @ 70 MPH and stock size tires (30.5 inch dia.) thats around 1916 RPM with an Auto w/OD (depending on the OD ratio). It would run about 2462 RPM with 4.56 gears, all else being the same....... that will make a significant DROP in mileage.
Ain't no free lunch, more power = less fuel mileage (unless your in a diesel)

So your saying that when me and a fellow member took the same exact 2.5 hour trip, cruising at the same speeds, very similar applications, him with 3.55's and me with 4.56's, that he would get 19mpg during the same route that i got 22mpg??? and that our trip comp's that showed us these numbers were part of a conspiracy against 4.56 gear owners???

Lemme ask you something... do you have 4.56 gears in your truck? do you personally know anyone that has a 5500# truck that went from a 3.55 gear ratio to a 4.56 gear ratio and have reported a... and i quote... "a significant DROP in mileage?" ... didnt think so

Not bashing you (or maybe you think i am, idc) but i personally know the ramifications on my truck with the 4.56 gears vs. the 3.55's and there was a significant INCREASE in gas mileage...

-David

PS i DO agree with the fact that 4.56's will be a bit much in his application, but 4.10's would be a nice step up with, i believe, better MPG and signifact acceleration improvement

 

[eatsleepdrivesc]

Yep on that trip david i was getting 19 and he was getting 22 moving at the same mph

 

[dale3fan3]

WHo was leading and who was drafting ? LOL

 

[mmmhoss]

Thanks for the input.

I am starting to think that the 4:10 gears may be the better choice.

The mechanic also stated that it might be cheaper to find a rear end in a salvage yard with the gears I want, plus get a posi track limited slip.

He seems to be conscerned with putting new gears in the rear end. He said that it is always asking for trouble. The gear swap could go wrong. End up getting a whine, or whurr when you let off the gas.

I think he is trying to be honest and up front. He has always been a good mechanic in the past.

 

[Exxon]

I guess in the mpg conspiracy, it would be the same as a underdrive pulley, you're engine works less which equals greater efficiency. but it would have to be in your ideal horsepower or torque range (don't quote me)

 

[eatsleepdrivesc]

You might wanna go find a place the specializes in Gear replacements and such...

 

[dale3fan3]

Thanks for the input.

I am starting to think that the 4:10 gears may be the better choice.

The mechanic also stated that it might be cheaper to find a rear end in a salvage yard with the gears I want, plus get a posi track limited slip.

He seems to be conscerned with putting new gears in the rear end. He said that it is always asking for trouble. The gear swap could go wrong. End up getting a whine, or whurr when you let off the gas.

I think he is trying to be honest and up front. He has always been a good mechanic in the past.

you could do the salvage yard and get 3.92 gears and the factory lsd but then your still dealing with the dreaded clip issue that goes with it. Find a competant gear installer and get yukons and a dtt and dont look back.

 

[dale3fan3]

Where are you from someone here might be close to you and be able to recommend a installer for you.

 

[ce2flaco]

Seems like your guy is a bit nervous...i would go elsewhere for the install.