4.56 for 3.8
08-12-2013, 11:44 PM
#21
JK Freak
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2600-2800 rpm at highway speeds won't kill a 3.8L.
In fact, with a 2,000 trailer, you likely won't need to run in 5th gear like we did with a loaded 4 dr pulling a 3500 lbs trailer. Unless you come to the Rockies, 6th gear with 35s and a small trailer, with 4.88s will work.
In fact, with a 2,000 trailer, you likely won't need to run in 5th gear like we did with a loaded 4 dr pulling a 3500 lbs trailer. Unless you come to the Rockies, 6th gear with 35s and a small trailer, with 4.88s will work.
Like I said I don't do hardcore wheeling or rock crawling to go to a super steep gear set.
08-13-2013, 03:12 AM
#24
JK Super Freak
I guess it all comes down to what makes the most sense for you. And if like said there is only 150-180rpm difference between 4:88 and 4:56, why not choose the stronger of the two. The lower you go the smaller and potentially weaker the pinion. My gear guy who does nothing more than build differentials said that he would never gear lower than 4:56 in a Dana 30. I trust that he would know. It made a huge difference and I enjoy my jeep so much more now.
08-13-2013, 04:22 AM
#25
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Hello,
I have 4.56 with 35" MTR/Kevlar and my Jeep is manual.
On the Highway at 60Mph the engine run at 2240rpm in gears 6. It the perfect ratio for a good power and a good fuel economies.
If you think to pass to 37" tires put 4.88 but if your idea is to stay with 35" put 4.56 is the perfect ratio for that.
I have 4.56 with 35" MTR/Kevlar and my Jeep is manual.
On the Highway at 60Mph the engine run at 2240rpm in gears 6. It the perfect ratio for a good power and a good fuel economies.
If you think to pass to 37" tires put 4.88 but if your idea is to stay with 35" put 4.56 is the perfect ratio for that.
08-13-2013, 04:44 AM
#26
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Running 3000-3500 is high rpm I can bet you weren't doing more than 12mpg if not worse. That's my whole problem I want something that will pull about 2-2.5k trailer an still be able to run between 2500-3000 rpm on the highway when I not towing.
Like I said I don't do hardcore wheeling or rock crawling to go to a super steep gear set.
08-13-2013, 04:51 AM
#27
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4:10
I am running 4.10's with 35" duratracs and I have a 6 speed manual. 6th gear is still pretty useless. When I am on the highway on hills I use 4th or 3rd a lot of the time to stay at speed. With that I am really looking at going to 4.88
08-13-2013, 05:18 AM
#28
JK Freak
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Well I think what it comes down to 4.56-4.88 so its seems ill be running right were I'm at not on RPM's but in 1-2 gears higher which is what I ultimately want.
Thanks for everyone ones opinion on everything. After I choose ill be sure to post my results
Thanks for everyone ones opinion on everything. After I choose ill be sure to post my results
08-13-2013, 07:04 AM
#29
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I guess it all comes down to what makes the most sense for you. And if like said there is only 150-180rpm difference between 4:88 and 4:56, why not choose the stronger of the two. The lower you go the smaller and potentially weaker the pinion. My gear guy who does nothing more than build differentials said that he would never gear lower than 4:56 in a Dana 30. I trust that he would know. It made a huge difference and I enjoy my jeep so much more now.
While there would be a strength concern running 35s on a low pinion Dana 30 with 4.88s from a TJ/XJ, there isn't a concern in a JK high pinion Dana 30.
Chromoly axle shafts will break before 4.88s in a JK Dana 30.
If your gear guy is familiar with the differences between high and low pinion design and the substantially larger pinion shaft on the JK vs TJ/XJ, I'm sure he would qualify his opinion about 4.56s being the max not applying to the JK.
08-24-2013, 02:22 PM
#30
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Just picked my JKU(08 3.8 6speed stock tires) today. I had 4.56s installed and wished I had gone 4.88s. There is a difference but would like more. 70mph 3000rpm 15mpg. Plan on going to 33x12.50 someday and concerned it won't be enough. I didn't have to downshift on hills at all. 6th gear and pulled right threw them hills but still feel like when I go to 33s I will want lower gearing. Can't wait to see the difference on the trails