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NW_Jeep

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Well I guess gears could be on upgrade list. With the torque I’m hoping I’ll be fine on 38’s but I guess I’ll get the gears I want
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MNMJD

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Not sure if this has been posted yet - if duplicate sorry
 

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As most of us know the diesel will have a different trans than either the 2.0 or the 3.6 (3.0- 8HP 75 vs 8HP 50 for the other two). Here is a chart showing the differences in gearing, in case anyone is interested.
 

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As most of us know the diesel will have a different trans than either the 2.0 or the 3.6 (3.0- 8HP 75 vs 8HP 50 for the other two). Here is a chart showing the differences in gearing, in case anyone is interested.
I wish my mechanical knowledge was sufficient enough to understand that table.

So is 8HP 75 more betterer than 8HP 50?
 

BuffaloBill

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If you wanted to calculate for example, the engine rpm in 8th gear for say 60mph, it’s pretty straightforward:

The tire info for the stock Rubicon K02 tire shows 635 revolutions/mile (tirerack’s data).
60mph is 1 mile/minute.
Therefore a tire rpm of 635 would produce 60mph.
With 3.73 axle ratio, the drive shaft spins 635 X 3.73 = 2369rpm (rounding up).
From that table, the overall trans ratio in 8th is 0.64.
So the engine rpm then, is 2369 X 0.64 = 1516rpm.

Any other speed would just be a ratio of the above. If traveling 75mph, the engine rpm would be:
(75 x 1516)/60 = 1895rpm

I imagine the tire mfg’s data might be at rated load and pressure? The load and pressure we run on the JL might result in a slightly different rev/mile. But I think that effect would be small. At higher speeds the rev/mile decreases a tiny bit also. But I’d expect the real life rpm to be pretty close to calculated.

Are they building our Jeeps yet?
 

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I wish my mechanical knowledge was sufficient enough to understand that table.

So is 8HP 75 more betterer than 8HP 50?
75 is good for 750Nm of torque, 50 is good for 500Nm. The 75 will have different software to tailor the shift points to an engine with lots of low-end torque. Other than that, essentially the same transmission.
 
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JLURD

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If you wanted to calculate for example, the engine rpm in 8th gear for say 60mph, it’s pretty straightforward:

The tire info for the stock Rubicon K02 tire shows 635 revolutions/mile (tirerack’s data).
60mph is 1 mile/minute.
Therefore a tire rpm of 635 would produce 60mph.
With 3.73 axle ratio, the drive shaft spins 635 X 3.73 = 2369rpm (rounding up).
From that table, the overall trans ratio in 8th is 0.64.
So the engine rpm then, is 2369 X 0.64 = 1516rpm.

Any other speed would just be a ratio of the above. If traveling 75mph, the engine rpm would be:
(75 x 1516)/60 = 1895rpm

I imagine the tire mfg’s data might be at rated load and pressure? The load and pressure we run on the JL might result in a slightly different rev/mile. But I think that effect would be small. At higher speeds the rev/mile decreases a tiny bit also. But I’d expect the real life rpm to be pretty close to calculated.

Are they building our Jeeps yet?
No and they probably won’t until the EPA/CARB certify the emissions/fuel efficiency.
 

BuffaloBill

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No and they probably won’t until the EPA/CARB certify the emissions/fuel efficiency.
Yeah, when on Jeepchat yesterday I asked if they had any insight on the epa date. But they did not.
 

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Just found this on the CARB website. It is dated today but the doc is dated 10/17. Can somebody smarter than I, tell me if this is what we are waiting on?
 

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JLURD

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Just found this on the CARB website. It is dated today but the doc is dated 10/17. Can somebody smarter than I, tell me if this is what we are waiting on?
Executed 10/1 re CARB emissions certification. Seems the EPA fuel efficiency certification is the only missing piece at this point then. Would be interesting to know how many other vehicles are “deficient” in CA’s OBD requirements and paying fines to the tune of hundreds of dollars per vehicle. Would also be nice to know how egregious the requirements are (likely very given the millions in fines) and how it’s being baked into the cost of every vehicle.
 

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If you wanted to calculate for example, the engine rpm in 8th gear for say 60mph, it’s pretty straightforward:
Thanks for this. I saved this in my note-keeping app for future reference.
 
 



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