Jeep Garage  - Jeep Forum

Jeep Garage - Jeep Forum (http://www.jeepgarage.org/forums.php)
-   Engine Performance/Intakes/Exhausts (http://www.jeepgarage.org/f108/)
-   -   Upgrading Axle Ratio (http://www.jeepgarage.org/f108/upgrading-axle-ratio-17492.html)

Lazzman 01-15-2011 01:16 PM

Upgrading Axle Ratio
 
I have the 2011 GC with the 3.6L V6 and the only available 3.07 axle gearing.

As anyone knows 3.07 is a highway gear and will not provide the full range of power the engine has to offer.

I am hoping that I can upgrade to the Hemi 3.47 gears.

My last vehicle was an Explorer Sport 4.0 V6 with the 4.10 axle ratio- the engine has no where near the power of the Chrsyler 3.6 but the gearing is much better. B

Fuel milage is not a big concern as both Vehicles are 5 spd auto and the jeep get a little better milage on the highway- my average mile per gallon is 18- according to the onboard computer. The Explorer is about 16 All around and the engine is bigger and less efficient. There should not be a significant fuel difference with the taller gears installed in the jeep.

I am wondering if this would be a direct swap and if it would void any warranties? Does the Hemi have the same Axle housing as the V6? I am sure the Hemi axle ratio gears could be purchased and installing them is not that big a job.

I understand gas milage but 3.07 in not a good off the line gear or towing gear, sure it is good for gas milage but you are loosing a lot of the engines capabilities. Especially with the V6 which has to rev high to make its power- and after all it is a truck.

Thanks

JDM12 01-15-2011 01:47 PM

Re: Upgrading Axle Ratio
 
Quote:

There should not be a significant fuel difference with the taller gears installed in the jeep.
There probably won't be, and there will not be a significant difference in low end grunt either. Your engine speed will raise about 200 rpm at 65mph with a 30 inch tall tire. Sounds like a fun project tho.

Lazzman 01-15-2011 04:15 PM

Re: Upgrading Axle Ratio
 
So your saying no difference in acceleration, that is hard to believe.

Generally swapping gears for a taller ratio will drop 1/4 mile times by .5 second. Generally speaking if you pulled 3.08's and installed 3.55's you would feel the differrence. I had it done to my '90 Mustang 5.0 and it made a big difference, though that engine had a much lower powerband than the Jeep 3.6

With Taller gearing rpm's will also build quicker and the Rpms will drop higher after each gear change.

At full throtttle my Explorer would Shift at 6000rpm and the tach would only drop down to 5000rpm in the next gear because of those 4.10's- Keeping the engine in the powerband.

With the jeep it goes to 6500 rpm and then drops down below 3000rpm after the shift- this is way below the power band and takes time to rev back up. It should be a one two punch to be effective otherwise the gearing is too low for the engine RPM's. That is so weak that Chrysler put 3.07 gears in the axles- totaly inhibits the engines high reving usable power.

I could rant all day about Jeep doing this :motx:

I guess the ideal solution would be to wait for the 8 speed transmission. Then you could have 4.55 gearing for awesome off the line power and still get kick ass gas milage with the three overdrive gears on the highway.

mjw930 01-15-2011 05:37 PM

Re: Upgrading Axle Ratio
 
The W5A580 trans mated to the V6 has a lower 1st gear to compensate so your effective ratios are pretty much the same. All other gears are also lower, as you would expect based on the 3.07:1 rear.

V6 V8
1st .........3.59.......... 3.00
2nd ........2.19......... 1.67 upshift / 1.50 kickdown
3rd......... 1.41...........1.0
4th...........1.00........ 0.75
5th .........0.83 .........0.67
Reverse ..3.16......... 3.0

Your effective ratios are

1st - 11.02 10.41
2nd - 6.72 5.79
3rd - 4.33 3.47
4th - 3.07 2.60
5th - 2.55 2.32

Of course you would get a better multiplier with the 3.47 rear but I seriously doubt you would see that much extra seat of the pants performance. And yes, it would probably void your entire drivetrain warranty and the cost to do it is probably more than the $1900 upgrade to the hemi. If you really want that ratio my suggestion would be to trade yours in on a V8.......

JDM12 01-15-2011 05:53 PM

Re: Upgrading Axle Ratio
 
Final drive in the hemi with 3.47 and in your vehicle with 3.07 is almost identical. So if in this case the 3.07's are "highway" gears, so are the 3.47 in the hemi. Lower gearing in your trans needed the higher gearing in your differentials.

Quote:

At full throtttle my Explorer would Shift at 6000rpm and the tach would only drop down to 5000rpm in the next gear because of those 4.10's
I'm not doubting this, but it is due to the gearing between your transmission and it's interaction with your torque converter. There is still the same amount of "gearing" in between each gear. Changing your diffs out will not make the gaps in your transmission gearing get any smaller.

I haven't driven one but it sound like for your needs...the upcoming 8 speed would be more suitable. enjoy the vehicle!

Lazzman 01-16-2011 11:21 AM

Re: Upgrading Axle Ratio
 
yes that makes sense, I understand now.

Crazy thought but it was worth discussing.

Thanks for clarifying this :D

AIR_RAM 04-30-2011 09:47 AM

Re: Upgrading Axle Ratio
 
Yes but changing your gear ratio will increase the mechanical advantage on those transmission gears.... So effectively each gear in the transmission will have MORE torque to move forward. This will lower the load on the engine and transmission effectively moving the load to the rear. So what you would get is less stress on the engine/transmission while at the same time increasing the fuel economy and off the line acceleration and towing capability.

Also, upgrading to the HEMI is not a valid fix since the HEMI comes OVER GEARED as well... With an overall gear ratio of 2.60/2.32 in overdrive... that’s lethargic and the reason why it cannot hold that .67 gear in overdrive with MDS on. The wk2 is geared completely WRONG and will see drastic improvements in fuel economy and low end performance by correcting the gear ratios to 4.10 or even 4.56's depending on tire height!

This has already been proven with the Rams over the last 10 years with the same engine/transmission/gear ratios... So it may be NEW "Math" to many here in the Jeep forums... but its common knowledge on the Ram side.

Simple math is all you need to see the light.

First find your overall gear ratio:
Trans Gear x Rear Gear = Overall Gear Ratio (OGR)

Second find your RPM at any speed:
SPEED x OGR x 336 / TIRE HEIGHT = RPM

From experience with the 545RFE and gearing... we have found that for best results you should aim to achieve 2001RPMs at 60MPH. <--- This will give you the best MPG while offering you outstanding towing capability and off the line acceleration.

Also, RPMs alone do NOT dictate fuel economy... its the "LOAD" on the engine at any given RPM that has more effect on your fuel economy than RPMs alone.


SPEED SAFE, NICK

77rednecktruck 05-01-2011 10:32 AM

Re: Upgrading Axle Ratio
 
Quote:

Originally Posted by AIR_RAM (Post 406599)
Yes but changing your gear ratio will increase the mechanical advantage on those transmission gears.... So effectively each gear in the transmission will have MORE torque to move forward. This will lower the load on the engine and transmission effectively moving the load to the rear. So what you would get is less stress on the engine/transmission while at the same time increasing the fuel economy and off the line acceleration and towing capability.

Also, upgrading to the HEMI is not a valid fix since the HEMI comes OVER GEARED as well... With an overall gear ratio of 2.60/2.32 in overdrive... thatís lethargic and the reason why it cannot hold that .67 gear in overdrive with MDS on. The wk2 is geared completely WRONG and will see drastic improvements in fuel economy and low end performance by correcting the gear ratios to 4.10 or even 4.56's depending on tire height!

This has already been proven with the Rams over the last 10 years with the same engine/transmission/gear ratios... So it may be NEW "Math" to many here in the Jeep forums... but its common knowledge on the Ram side.

Simple math is all you need to see the light.

First find your overall gear ratio:
Trans Gear x Rear Gear = Overall Gear Ratio (OGR)

Second find your RPM at any speed:
SPEED x OGR x 336 / TIRE HEIGHT = RPM

From experience with the 545RFE and gearing... we have found that for best results you should aim to achieve 2001RPMs at 60MPH. <--- This will give you the best MPG while offering you outstanding towing capability and off the line acceleration.

Also, RPMs alone do NOT dictate fuel economy... its the "LOAD" on the engine at any given RPM that has more effect on your fuel economy than RPMs alone.


SPEED SAFE, NICK

good post. I can't believe people are saying there will be little change when upping read end ratio's.

I have the hemi and would love to throw 4.10's in there.

My old car (2005 Crown Vic) got better gas mileage at a higher speed and RPM because it was easier for the car to hold itself at speed, partly because it had the 2.73 ratio in the rear end. :( :)

Diablo169 05-02-2011 10:15 AM

Re: Upgrading Axle Ratio
 
Hello all. I honestly wouldn't be surprised if it got better gas mileage from switching the lower, numerically higher, gears. Where I live the is a lot of hills, and my 3.6 is constantly shifty and pulling in the 3,000 rpm range.

By switching you would also be able to step up to a slightly taller tire.

The 3.6 is great on power, but these WK2's are beasts.

If I had my choice I'd go 3.73 (if available) 2.5" Lift and some 32-11.50's and a rear limited slip.

JDM12 05-02-2011 10:55 AM

Re: Upgrading Axle Ratio
 
Quote:

Originally Posted by 77rednecktruck (Post 406999)
good post. I can't believe people are saying there will be little change when upping read end ratio's.

I have the hemi and would love to throw 4.10's in there.

My old car (2005 Crown Vic) got better gas mileage at a higher speed and RPM because it was easier for the car to hold itself at speed, partly because it had the 2.73 ratio in the rear end. :( :)

Quote:

Originally Posted by Diablo169 (Post 407627)
Hello all. I honestly wouldn't be surprised if it got better gas mileage from switching the lower, numerically higher, gears. Where I live the is a lot of hills, and my 3.6 is constantly shifty and pulling in the 3,000 rpm range.

By switching you would also be able to step up to a slightly taller tire.

The 3.6 is great on power, but these WK2's are beasts.

If I had my choice I'd go 3.73 (if available) 2.5" Lift and some 32-11.50's and a rear limited slip.

If you anticipate an increase in both fuel economy and performance from a gear swap than can someone please explain why Chrysler chose the final drive ratio/s they did.

77rednecktruck 05-02-2011 11:38 AM

Re: Upgrading Axle Ratio
 
Quote:

Originally Posted by JDM12 (Post 407646)
If you anticipate an increase in both fuel economy and performance from a gear swap than can someone please explain why Chrysler chose the final drive ratio/s they did.

don't know. I have upgraded the rear end ratio in 3 of my previous cars and it made them all better. My old 92 mustang had 3.55 and I went to 3.73 but it was not enough, once I went to 4.10 it got a lot better.

Why are cars sold with their horrible air intake design? Why are cars shipped with crappy tires on them? Why do cars have exhausts from the factory that are more restrictive than a straw from McDonald's? If dealers did everything the right way from the factory, there would be no need for aftermarket companies. :)

JDM12 05-02-2011 07:14 PM

Re: Upgrading Axle Ratio
 
Quote:

Originally Posted by 77rednecktruck (Post 407690)
Why are cars sold with their horrible air intake design? Why are cars shipped with crappy tires on them? Why do cars have exhausts from the factory that are more restrictive than a straw from McDonald's? If dealers did everything the right way from the factory, there would be no need for aftermarket companies. :)

1. To keep the intake noise down, and probably cost effectiveness.

2. A mix between cost, road manners, and noise.

3. Cost, noise, emissions.

Back to the gearing question, assuming gear ratio X costs the same to manufacture and install as gear ratio Y, which it should, why would Chrysler engineers completely ignore a practically free method to increase both performance and mileage?


All times are GMT -5. The time now is 06:44 AM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright 2012 - JeepGarage.Org
The Jeep Grand Cherokee Owners Community