Regearing 4:56 vs 4:88
- Thread starter Ratbikerod
- Start date
Yea, that was definitely one of the deciding factors when I bought my JK. I did not want all of that. My buddy bought a JL about the same time and we have both been doing typical upgrade stuff. His is 50% more difficult and costly than on my JK.
I wonder, if we were to ping the folks who bought a new Wrangler in late-2018/early-2019, particularly those deciding between leftover JK's or new JL's, if the transmission/drivability was a major influence to their decision. I remember my first JLU rental, it was a 2019 white Sahara with the 2.0L. It felt considerably faster than the white 2018 JKU Willys I had as a rental just a few weeks prior. I couldn't tell about any gas mileage differences, since one was rented in rural Colorado (Durango) and the other in SoCal.
I don't fit well in the 2011+ JK interiors or JL interiors, so for me that was never really an option. Honestly I'd love a 392 Rubicon but I could never write a check for that much $$$ and have a vehicle I could barely drive for more than 2 hours at a time (they both kill my back/shoulders, as I'm forced to "lean" away from the door to get comfortable).
Given the cost of a JL, plus their quirks and known issues, it would certainly come down to preference, willingness to spend more $$, and consideration of money already spent. For example, if you've got a nicely built JK and are looking to extract some better drivability, $5000 is fairly inexpensive (though realistically it's probably half that for most DIY'ers). Couple that with the nightmare of selling your JK, recouping as much of a % as possible on parts you've added, then buying a JL and replacing those parts you had on the JK to get it to the same level.
To be fair, no engine or transmission combo will completely make up for improperly geared axles
The 5.13's we put in my daughter's Islander made a massive improvement and was money well spent...
This is the root of my dilemma to be brutally honest. By the time I do what I want to my JK I would be better off, financially, waiting for a few years for used JL with the XR package to reduce in price a bit more. There are things I like better with the JK, however.
We're about ready to move so I have some more time to contemplate and ping pong the options!
To your point, I expect the 4:88's will wake my JK up significantly. I am just gathering the funds to get it done and hope to do so this month.To be fair, no engine or transmission combo will completely make up for improperly geared axles
I expect that most of my driving and off-roading will be improved with this change with a slight suffer on the highway at 70.
Going to an 8spd will to certain extent. Just look at the gear ratios in the first 5 gears for an apples-apples comparison:
Mechanical advantage improvement is as follows:
1st: 131%
2nd: 143%
3rd: 149%
4th: 167%
5th: 155%
Average is 149%. An 8spd w/ 3.73 FDR would be roughly comparable to having a 5spd w/ 5.56 FDR (3.73*1.49). Not to mention you have access to the 3 additional gears. Even if you only use the 1st gear improvement as a multiplier it would be equivalent to a 4.89 (3.73*1.31) with the 5spd.
Yeah it's not exactly the same - it will make better use of engine rpm and account for tire size increase but moves where the torque multiplication happens. That may actually help those sticking with the d44/d30 combo, however, and are only doing light off-roading.
Many of the JLs come with a 3.45, which would be like a 5.13 with a JK 5spd. No wonder the JLs feel so snappy!
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How I see it, you really can't compare the 5 gears in the NAG1 directly to the first 5 gears of the 8HP70, at least not in any "apples to applies" attempt. Looking at differences in transmissions with a mismatching # of gears is better on a graph than a table, as you'd get to see the overlapping RPM vs road speed comparisons.
In table form, I think it would be more accurate to compare them side by side like this:
In 1st gear, the 8HP has a clear advantage, but it will shift into second gear at a much lower road speed than the NAG1, at which point the torque multiplication advantage of the NAG1 first gear beats that of the 8HP (for the sake of this discussion, let's just ignore the differences in parasitic losses between the two). As the NAG1 approaches its max road speed for 1st gear and switches to 2nd gear, the 8HP70 would be close to shifting into 3rd gear, where the NAG 1 would still have the torque multiplication advantage.
Of course we would expect a meaningful change in the acceleration times thanks to the better utilization the available power range and maintaining a higher average torque multiplier across the operating range of the 3.6L. We can see this when we compare the 3.6L JLU 1/4-mile times to the 3.6L JKU 1/4 mile times. The JLU consistently pulls ~15.3 sec @ ~90 mph, which beats a comparable JKU by ~1.4 seconds and ~7 mph. Note that that some of the differences between the two is due to the ~200 weight savings of the JLU and better aerodynamics. Using some old Rules of Thumbs, you can probably attribute ~1.0-1.2 second of improvement due to the transmission differences. This is significant by any measure and is exactly why on Wranglers and other vehicles, with all things being equal, the 8HP equipped rigs feel like they got a massive power bump!
Certainly the 8HP would perform better on slower speed/technical trails (all things being equal), but I would argue that for day-to-day drivability, either transmission with poorly geared axles would still suck. Why? Well because the biggest issues experienced with undergeared axles are almost always the poor drivability in 1:1 and overdrive gears (or overdriveS in the case of the 8HP). In many cases, the next closest gear to the 1:1 ratio (3rd gear in the case of the NAG1) also has perform drivability.
Imagine trying to spin 35"s and maintain highway speeds on a NAG1 running 3.73's in the axles. You'll be lugging the engine, forcing excessive downshifts and/or applying more throttle to maintain speed (requiring more torque input - aka throttle - to the rear than would be necessary), causing excessive wear and tear on the driveline and axles.
But would an 8HP fix that? And what about an 8HP + poor axle gears vs a NAG1 + good axle gearing? Let's do a comparison: We will use 70 mph and the gear ratio I would go with for 35"s if I were building a 2012+ and running the stock driveline (5.13's). In OD, you'll be cruising fine at ~2860 rpm and could comfortably drop down into 4th gear (1:1) if you had a long hill or needed to pass someone.
Looking at the same parameters, but this time with an 8HP70 and poor axle gearing (we'll use the common 3.73 ratio as many JKs come with this from the factory). In 8th/OD2, you'll be cruising at just under 1700 RPM. Unless you're driving downhill, any change in road grade or wind resistance and you'll instantly be back in 7th/OD1. You'll be able to manage 7th in some cruising instances, but your engine RPM is still a paltry ~2100 RPM, and will almost certainly be jumping down to 6th often, and 5th occasionally, to maintain speed... at least based on my experience here in Hilly PA (those in Florida need not apply haha). The likely scenario is that you'll hopefully be able to turn "ECO" mode off and stay out of 8th gear as much as humanely possible (heck, I do this in my wife's 2017, 3.6/8-speed Grand Cherokee running stock 31.5" tires). You'll be using 4 gears to cover what 2 gears successfully manages on the NAG1+good gearing.
Given the two options, a NAG1+proper gearing vs 8HP70+poor gearing, I would take the NAG1 any day. Actually, that isn't true, I'd take the 8HP and would regear my axles to really take advantage of the extra gears, you get my point
A fun tidbit I found when trying to find verifiable 1/4 mile times for the 3.6L JLU - the 2.0t JLU often beats the 3.6L
@pc1p, you are a wealth of information. Thank you so much. That above post is stellar!
This quote is how I feel right now with 3:73 on 33's - "Imagine trying to spin 35"s and maintain highway speeds on a NAG1 running 3.73's in the axles. You'll be lugging the engine, forcing excessive downshifts and/or applying more throttle to maintain speed (requiring more torque input - aka throttle - to the rear than would be necessary), causing excessive wear and tear on the driveline and axles."
This quote is how I feel right now with 3:73 on 33's - "Imagine trying to spin 35"s and maintain highway speeds on a NAG1 running 3.73's in the axles. You'll be lugging the engine, forcing excessive downshifts and/or applying more throttle to maintain speed (requiring more torque input - aka throttle - to the rear than would be necessary), causing excessive wear and tear on the driveline and axles."