Novak Conversions Jeep Wrangler TJ radiator

Question about re-gearing

tlord

tlord

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I've been looking into regearing my '04, currently sitting on close to 31 inch tires I believe. Even though its not on 35s or anything, I'm definitely looking at trying to get a faster feel out of the car. Yes, it's a TJ, it'll never really be fast and I don't have the money for forced induction at the moment unfortunately. However, I'm curious to hear yalls experience with the car before and after regearing. Is it really a noticeable difference? I was thinking about upping to 4.56 considering I might up the tire size in the future, and I'm really looking for that quick feeling. This thing may be slow but it gets driven like a sports car I must admit. Thoughts on gear ratios/experience with the feel of the car are greatly appreciated. (Also, I'd probably just swap the entire axles with some factory 4.56s I found, sounds like it'll be cheaper than a shop regear.) Thanks
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tlord said:
I've been looking into regearing my '04, currently sitting on close to 31 inch tires I believe. Even though its not on 35s or anything, I'm definitely looking at trying to get a faster feel out of the car. Yes, it's a TJ, it'll never really be fast and I don't have the money for forced induction at the moment unfortunately. However, I'm curious to hear yalls experience with the car before and after regearing. Is it really a noticeable difference? I was thinking about upping to 4.56 considering I might up the tire size in the future, and I'm really looking for that quick feeling. This thing may be slow but it gets driven like a sports car I must admit. Thoughts on gear ratios/experience with the feel of the car are greatly appreciated. (Also, I'd probably just swap the entire axles with some factory 4.56s I found, sounds like it'll be cheaper than a shop regear.) ThanksView attachment 669172
Click to expand...

In general, yes, deeper gears will be noticeable, but you want the right gearing for your final tire size.

What’s your current gear ratio?
What transmission do you have?
What engine?
What final tire size?

The 4.0 performs better with more than the average rpm’s. If they are too low the response is anemic. So getting it right is key to getting that quicker and faster feeling.
 
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Swapped them in my jk. Went from 3:21 to 4:10. On 3:21 the seven speed tranny stayed in third gear driving out to California with the westerly head winds. After going to 4:10 she drove like a rocket in seventh. Didn’t change gears every time the wind blew.
 
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My daily driver is a properly fast sports car. The TJ ain't that. The TJ is loads of fun in its own way, but it doesn't compare. If you want that, loads of options are out there at decent prices and you'll probably be happier and save money in the end.

Despite it's reputation, the 4.0L doesn't make huge torque down low and 190hp at peak wasn't setting the world ablaze either. The power band from 3200rpm peak torque to 4500rpm peak hp is narrow compared to more modern engines. The gearing change is about changing the rpm at a given speed in a given gear to move up that curve. It does not make the 4.0L more powerful, it just puts you in a higher power part of that curve. And this is noticeable, but it's still only 190 hp at most. It's not like dropping a modern V-8 in it.

You should plug your transmission and tire size into this tool linked below and get a sense of what various gear ratios will do. You are probably on 3.73 gearing now. There is a table where it gives rpm at a speed and you can change the speeds calculated. The ratios available are 4.10, 4.56, 4.88, 5.13, 5.38. You may also have to change differential carrier. At highway speeds each gearset step increases rpm by around 200.

https://www.grimmjeeper.com/gears.html

Then plot the rpm at current and new gear ratio at speeds you care about against the factory curve to see the difference in max power available.

1753736795488.jpeg
 
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Your profile shows 4.0 with auto. With your stock size tires I wouldn't bother with regearing. Just turn the OD off unless you're cruising on the highway at 70.
 
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elalich said:
4.56 on 31's is a bit much, you'd be taching around 3000 rpm in overdrive at 65 mph. They are dead on for 35's. A 4.10/11 or 4.27 gear set is pretty nice driving.
Click to expand...

4.56 is a terrible choice for 35s with the 42rle. OP would need 5.38s for 35" tires. My 06 TJ cruised at 2500 RPM at 70 mph with this setup.
 
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Duck Doctor said:
4.56 is a terrible choice for 35s with the 42rle. OP would need 5.38s for 35" tires. My 06 TJ cruised at 2500 RPM at 70 mph with this setup.
Click to expand...

I disagree. I am on 35s and the stock 4:10 gearing. The only time I have issues is at highway speeds on long grades. But the 4.0s are so weak that it's a problem regardless. And by "problem" I mean I can barely break 70 MPH on those long grades. It doesn't happen much so no biggy.

I will ultimately do a gearing change to reduce stress on the transmission, but I'll go to 5:13s which is plenty for 35s for the driving I do. I live in the Cascades, so there is climbing for sure, but the elevation isn't as high as Colorado.

To the OP - what diff ratio do you have now? 3:07? 3:73?
 
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nevada72 said:
I disagree. I am on 35s and the stock 4:10 gearing. The only time I have issues is at highway speeds on long grades. But the 4.0s are so weak that it's a problem regardless. And by "problem" I mean I can barely break 70 MPH on those long grades. It doesn't happen much so no biggy.

I will ultimately do a gearing change to reduce stress on the transmission, but I'll go to 5:13s which is plenty for 35s for the driving I do. I live in the Cascades, so there is climbing for sure, but the elevation isn't as high as Colorado.

To the OP - what diff ratio do you have now? 3:07? 3:73?
Click to expand...

WEll if you were geared to 5.38 you wouldnt have issues at highway speeds. Until you drive a properly geared rig it will be impossible to convince you.
 
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I'm running 31.7 inch tires with 4.88 gears . I also have the 42rle transmission . Running around 2200 rpm @ 65 mph in overdrive . I drove it for several years with the same tire size and 3.73 gears . The difference is night and day . It would be fine with 4.56 also , I originally geared it for 33's and went back down to 32's .
 
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I'm running 33's (285/70-17) and 5.13s. Might be a little overkill for 33s at sea level, but it will eventually end up living at altitude with lower speed limits, and likely 35s at some point so it will be ready then. Previously was stock size and 3.73s. On the highway power is about the same, just enough to keep up with traffic but not a hot rod around town it is much more responsive and doesn't feel like it lacks power. The transmission shift point adjustments that can be made with HP Tuners seems like it could buy you one step lower gearing (like 4.88 instead of 5.13) since that makes the trans hold off a little longer on the 2-3 and 3-4 shifts, which really pull down the revs in the stock tuning.
 
Somewhere around here is about right...

42rle/31”/5.13=2877rpm @ 75mph
42rle/31”/5.38=3018rpm @ 75mph
 
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JMT said:
In general, yes, deeper gears will be noticeable, but you want the right gearing for your final tire size.

What’s your current gear ratio?
What transmission do you have?
What engine?
What final tire size?

The 4.0 performs better with more than the average rpm’s. If they are too low the response is anemic. So getting it right is key to getting that quicker and faster feeling.
Click to expand...

Current gear ratio should be 3.73, but I'll have to confirm that. Aside from that, it's the 42RLE/4.0 combo. I'd love to do 35's eventually, but that might not happen for a while.
 
GoldenGorilla said:
My daily driver is a properly fast sports car. The TJ ain't that. The TJ is loads of fun in its own way, but it doesn't compare. If you want that, loads of options are out there at decent prices and you'll probably be happier and save money in the end.

Despite it's reputation, the 4.0L doesn't make huge torque down low and 190hp at peak wasn't setting the world ablaze either. The power band from 3200rpm peak torque to 4500rpm peak hp is narrow compared to more modern engines. The gearing change is about changing the rpm at a given speed in a given gear to move up that curve. It does not make the 4.0L more powerful, it just puts you in a higher power part of that curve. And this is noticeable, but it's still only 190 hp at most. It's not like dropping a modern V-8 in it.

You should plug your transmission and tire size into this tool linked below and get a sense of what various gear ratios will do. You are probably on 3.73 gearing now. There is a table where it gives rpm at a speed and you can change the speeds calculated. The ratios available are 4.10, 4.56, 4.88, 5.13, 5.38. You may also have to change differential carrier. At highway speeds each gearset step increases rpm by around 200.

https://www.grimmjeeper.com/gears.html

Then plot the rpm at current and new gear ratio at speeds you care about against the factory curve to see the difference in max power available.

View attachment 669187
Click to expand...

This is a good point, and I'll try not to dump too much money into it like that. I'll definitely end up owning a sports car later on, but this is my first car and at the moment I lack the funds for that. Just trying to maximize the fun in the meantime, and this might be worthwhile if I end up going for larger tires later anyways. I appreciate that site too, that's very helpful, thanks.
 
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