So I went to 4.56 gears recently and wanted to provide a review. This is my specific results from my Jeep so I hope people don’t hold it against me if their results differ.
Original setup:
14 Jeep JKU Sport 3.6L AT
3.21 Gears
Offroad lights, Bumpers, Defender Roof Rack,
33” KO2 Tires, specifically 285/75R16 which hold a 32.75 ish diameter (No flashcal at this point)
1.75” front coil spacer.
New Setup:
4.56 G2 gears, same 30/44 axles
Same tires and accessories but added a .75” rear coil spacer.
Superchips Flashcal to set tire size and gear ratio.
My findings:
MPG
Prior to the new gears I had burned through 3-4 tanks of gas, only running about 14.5-15MPG (calculated 2% up to compensate for tire size change). After the regear and setting tires, I’ve been running 17-18MPG under the same driving conditions. Relatively flat, daily driver, stop and go rush hour traffics and late night outings)
I believe the main reason for this large change in MPG has to do with why I re-geared in the first place. I’ve found that adding the very HEAVY KO2 and mainly the increase to 33” tires was destroying the balance of the jeep. It had a most difficult time utilizing the 5th gear and I would either force it to 4th or just mash on the gas. Even while giving it a lot of gas, the RPMs would NOT go up. It was causing me a lot of stress on my knees and legs after a while, mainly because of the traffic and refusal to REV.
Also, to note is the general MPG reducers such as the 150+lb front bumper, and incredibly non-aerodynamic roof rack was the blame as well.
Now, the Jeep has NO problem holding 5th gear and the need to downshift has disappeared, however in it’s place is high revs. However, although the 3.6L is reving in the 2600 to 2900RPM range during high way speeds of 65-75MPH fuel economy has improved. Like I’ve read from a few other posts, it seems that the Pentastar engine favors and performs the best above 2k RPMs.
Power
Power is also a great gain as there is a noticeable change in all bands of gears. It’s great that it’s shorter and I look forward to testing how it performs on the trails. One thing to note however, is that with my current setup I’ve basically lost the option to reasonably cruise at speeds over 75MPH. I’ve noticed that the jump between 73MPH to 80MPH requires RPMs to hit 3k and also the aerodynamic hit is very steep. I could easily hit 80-85MPH and hold it, it will just drain the tank.
Conclusions:
I think that in all aspects going to the 4.56 gears was incredibly beneficial. However it did cost $1800 (material, labor, superchips, coil spacers). Was this a reasonable trade off? At my current financial situation it wasn’t too bad. ESPECIALLY considering I wanted to go 34” or 35” tires within the next few years. However, if I could do it again, I would get a superchips first to program the 33” tires in correct with the 3.21 before deciding to regear.
I also think, if you don’t plan on doing 35”+ tires, do NOT go to the 4.88 or higher gears, I think the RPMs at 70-75MPH would REV way to high. Unless you had a dedicated rig and not a daily driver, it would be a pretty steep hit across all the bands of transmission.
If you’re really concerned about MPG do NOT get a roof rack. On a daily driver I found it to be the most detrimental on fuel economy than any incremental upgrade I’ve done so far. K&N air filters also don’t do a spec of change to fuel economy and will only save you money if you keep reusing them. I can’t comment on CAI, but I doubt besides sounding awesome it will do much. (Although there’s probably some clear evidence sounding more powerful will psychologically make you feel +9HP)
I haven’t taken photos with the added .75” rears but here’s a few pics.
Original setup:
14 Jeep JKU Sport 3.6L AT
3.21 Gears
Offroad lights, Bumpers, Defender Roof Rack,
33” KO2 Tires, specifically 285/75R16 which hold a 32.75 ish diameter (No flashcal at this point)
1.75” front coil spacer.
New Setup:
4.56 G2 gears, same 30/44 axles
Same tires and accessories but added a .75” rear coil spacer.
Superchips Flashcal to set tire size and gear ratio.
My findings:
MPG
Prior to the new gears I had burned through 3-4 tanks of gas, only running about 14.5-15MPG (calculated 2% up to compensate for tire size change). After the regear and setting tires, I’ve been running 17-18MPG under the same driving conditions. Relatively flat, daily driver, stop and go rush hour traffics and late night outings)
I believe the main reason for this large change in MPG has to do with why I re-geared in the first place. I’ve found that adding the very HEAVY KO2 and mainly the increase to 33” tires was destroying the balance of the jeep. It had a most difficult time utilizing the 5th gear and I would either force it to 4th or just mash on the gas. Even while giving it a lot of gas, the RPMs would NOT go up. It was causing me a lot of stress on my knees and legs after a while, mainly because of the traffic and refusal to REV.
Also, to note is the general MPG reducers such as the 150+lb front bumper, and incredibly non-aerodynamic roof rack was the blame as well.
Now, the Jeep has NO problem holding 5th gear and the need to downshift has disappeared, however in it’s place is high revs. However, although the 3.6L is reving in the 2600 to 2900RPM range during high way speeds of 65-75MPH fuel economy has improved. Like I’ve read from a few other posts, it seems that the Pentastar engine favors and performs the best above 2k RPMs.
Power
Power is also a great gain as there is a noticeable change in all bands of gears. It’s great that it’s shorter and I look forward to testing how it performs on the trails. One thing to note however, is that with my current setup I’ve basically lost the option to reasonably cruise at speeds over 75MPH. I’ve noticed that the jump between 73MPH to 80MPH requires RPMs to hit 3k and also the aerodynamic hit is very steep. I could easily hit 80-85MPH and hold it, it will just drain the tank.
Conclusions:
I think that in all aspects going to the 4.56 gears was incredibly beneficial. However it did cost $1800 (material, labor, superchips, coil spacers). Was this a reasonable trade off? At my current financial situation it wasn’t too bad. ESPECIALLY considering I wanted to go 34” or 35” tires within the next few years. However, if I could do it again, I would get a superchips first to program the 33” tires in correct with the 3.21 before deciding to regear.
I also think, if you don’t plan on doing 35”+ tires, do NOT go to the 4.88 or higher gears, I think the RPMs at 70-75MPH would REV way to high. Unless you had a dedicated rig and not a daily driver, it would be a pretty steep hit across all the bands of transmission.
If you’re really concerned about MPG do NOT get a roof rack. On a daily driver I found it to be the most detrimental on fuel economy than any incremental upgrade I’ve done so far. K&N air filters also don’t do a spec of change to fuel economy and will only save you money if you keep reusing them. I can’t comment on CAI, but I doubt besides sounding awesome it will do much. (Although there’s probably some clear evidence sounding more powerful will psychologically make you feel +9HP)
I haven’t taken photos with the added .75” rears but here’s a few pics.
