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High Elevation Gear Ratio - 33's - 6-Speed (NSG370)

Rickyd

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the 6-Speed NSG370 seems to have pretty different gear ratios!
Its a 5 speed with a granny first. Only real difference from 5 speeds.

It allows sightly higher gearing than a 5 speed as you have the option of turning granny gear into more of a street gear by adding larger tires

Your drive ratio is axle x trans gear ratios.lower axle ratio changes will net you a lower crawl ratio and trans gears closer together in rpm at the cost of top speed. Gearing down will not make your jeep pull a pass easier for a given mph. It still takes the same power to get work done.

You should definitely have a different ratio like 4.10 or 4.56 for 33s regardless of where you live. But it won't give you more power.

If you want high altitude power you need increased compression ratio,forced induction or more cubic inches.

Some people mention fuel injection. It has nothing to do with pumping losses at altitude.

I have a 500hp truck. When i go to 5000ft and above guaranteed it is no longer 500hp. It may be passing everything else but it won't spin the tires at 70mph anymore,lol
 

Rickyd

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The NSG370s first is not a granny gear. 5.xx first ... possibly. 6.xx first ... definitely. 4.46 first ... nope.
Close enough. You take off in second gear on the street unless you put bigger tires on with stock gears. Doesn't change anything. 4,5,6 is close enough to 3,4,5 in a 5 speed for it to not matter. If it was a double overdrive like a t56 then i would agree that the assertion "it has pretty different gear ratios!" has relevance to the topic of being able to pull hills
 

JMT

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Y’all are ridiculous. This thread has exhausted its scope. Answer: 456 or 488, better to go 488 bc you’re already talking bigger tires. 513 even an option. Story over.
 

L J

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Close enough. You take off in second gear on the street unless you put bigger tires on with stock gears. Doesn't change anything. 4,5,6 is close enough to 3,4,5 in a 5 speed for it to not matter. If it was a double overdrive like a t56 then i would agree that the assertion "it has pretty different gear ratios!" has relevance to the topic of being able to pull hills
In my ten years of driving on 30.5s/4.10s I never took off in 2nd other than a couple of times just as a test. Also the 6 speed has a .84 overdrive as opposed to the .79/.78 overdrives of the 5 speeds. While not dramatically different it does make a difference on the highway when running 5.13s.

Y’all are ridiculous. This thread has exhausted its scope.
I wasn't aware that this was JMT'sblog.com.

:LOL:
 

Rickyd

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Im addressing " i want to be able to go 65 up hills on the highway" something gearing isn't going to solve so long as its within an acceptable range. Ax,nv or nsg has no relevance. Like jmt said.pick a ratio and be done,its easy.

To pull hills at altitude you still need more power.the 4.0l is a turd. No magic ratio is going to make it fast
 

rasband

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Im addressing " i want to be able to go 65 up hills on the highway" something gearing isn't going to solve so long as its within an acceptable range. Ax,nv or nsg has no relevance. Like jmt said.pick a ratio and be done,its easy.

To pull hills at altitude you still need more power.the 4.0l is a turd. No magic ratio is going to make it fast
Gearing is going to help solve it, because it helps put the engine into the power band better for the build.

I can tell you first hand that 4.10s vs 5.13s on 35s made a world of difference going through the mountains.
 

jjvw

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In my ten years of driving on 30.5s/4.10s I never took off in 2nd other than a couple of times just as a test. Also the 6 speed has a .84 overdrive as opposed to the .79/.78 overdrives of the 5 speeds. While not dramatically different it does make a difference on the highway when running 5.13s.


...

:LOL:
Agreed. I wouldn't treat the 6 speed any differently in how I would gear it compared to the 5 speed.
 
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BlueC

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If they had carboraters but they don't they are injected, and the air fuel mixture is corrected by the ECU.

Carb vs injector has nothing to do with the effects of altitude. (on the same engine, a properly tuned carb makes the same power as fuel injection, maybe even a little more depending on fuel, but we're way past the weeds with that discussion) It's all about atmospheric pressure, i.e. available air, and yes modern computers will adjust for this on the fly, applying more or less fuel to match the available air. (MAP sensor)

The OPs location states he is at 9100 ft in elevation. That has an atmospheric pressure of approximately 10.5 psi. Sea level is 14.7 psi. That nearly a 30% reduction in available air from sea level to the OPs location, which translates directly to engine power output.
 

jjvw

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Having driven past where the OP lives hundreds of times over many years, I can confidently say that gearing to about 3krpm at 75mph means he can drive up to the Eisenhower tunnel most of the way in OD and still hang on to 55mph at the top. Been there and done that many times. Now that mine is geared to about 2800rpm at 75mph due to a change in tire size, I need to spend much more time downshifting into lower gears. I liked my old lower gearing better, both on the highway, on city streets, and off road.
 

tworley

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Having driven past where the OP lives hundreds of times over many years, I can confidently say that gearing to about 3krpm at 75mph means he can drive up to the Eisenhower tunnel most of the way in OD and still hang on to 55mph at the top. Been there and done that many times. Now that mine is geared to about 2800rpm at 75mph due to a change in tire size, I need to spend much more time downshifting into lower gears. I liked my old lower gearing better, both on the highway, on city streets, and off road.
X2. My 5.13s are nice in that I can maybe drop down to 60 at the top of Eisenhower. The deep gears really help with the 10k' + passes we crest regularly.

Dont be afraid of the high RPMs. My last trip to summit county in the jeep I was holding 4-4.5k RPMs while racing @jjvw to the top. The 4.0s can handle it just fine.
 

Steel City 06

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Here is a bit more detail on why I almost always recommend 4.88 for 35s and 4.56 for 33s with the NSG370, and not the next higher ratio.

1652969502415.png

1652970852044.png

(Ignore the modified engine curves.)

You have two curves on the above chart, Engine Torque, and Engine Horsepower. Unfortunately, a lot of people conflate engine torque with torque at the wheel. While they are indeed directly correlated, that correlation only holds true when the overall effective ratio of engine revolutions to feet traveled holds constant. Any change in transmission gear, transfer case range, differential axle ratio, or tire size causes a proportional change to that ratio.

Horsepower is exactly proportional to torque times revolutions per minute. Thus, even when ratios or tire sizes change, an engine putting out a given amount of horsepower at a given instant will deliver a certain amount of horsepower at the wheels (neglecting negligible adjustments in drivetrain frictional and viscous losses).

To keep things short, the net effect is such that at a given road speed, propulsive force is directly proportional to the horsepower put out by the engine, irregardless of what ratio or tire sizes happen to be in between (provided that those ratios and sizes allow for the engine to be capable of producing that horsepower at that road speed).

So let's take a scenario. 4.56 ratio, 33" nominal (32" effective) tire radius, rolling up a hill at 75 mph. For simplicity, we'll use the Duratrac specification of 635 revolutions per mile.
6th - 3039 RPM
5th - 3618 RPM
4th - 4523 RPM

4.88 ratio, 33" nominal (32" effective) tire radius, rolling up a hill at 75 mph. (635 revolutions per mile.)
6th - 3353 RPM
5th - 3872 RPM
4th - 4840 RPM

In 6th gear and in 5th gear, you will notice that with 4.88 gears, the engine does indeed produce more horsepower at 75mph than it would with 4.56. 6th and 5th actually produce slightly more engine torque with 4.56s than 4.88s, but due to the ratio difference, 4.88 still delivers more propulsive force to the ground.

However, in 4th gear, notice that not only does the engine produce significantly more torque with 4.56 rather than 4.88, it also produces more horsepower. What this effectively means is that in 4th gear at 75 mph, you will get slightly  more propulsive force with the 4.56 gears than you will with the 4.88 gears. In addition, it will do so without bring you quite as close to redline, eliminating a bit of risk associated with holding those high RPMs for a long time.


...but what it you want to use 5th gear in place of 4th?

The answer is you need to gear far deeper than 4.88 to get 5th gear as useful as 4th is with a 4.56 ratio. In fact, in order to bring 5th as close to the peak HP RPMs as possible (4500-4600 depending upon the source), you would need to regear to 5.38 or even 5.89.


Another piece of food for thought: An internal combustion engine generally has peak thermodynamic efficiency when run at 100% throttle at or near the peak torque RPM. As you exceed the peak torque RPM, you still gain additional power capacity, but fuel consumption growth outpaces power production growth as RPMs increase. Essentially, you see diminishing returns on adding more fuel all the way from peak torque RPM to peak horsepower RPM, at which point increasing RPMs has a  negative correlation with power output, while simultaneously still increasing fuel consumption.

Since in either case, 6th gear is already straddling peak torque, there is little efficiency difference between the two ratios. In 5th, 4.56 holds a slight advantage in efficiency. In 4th, not only is less fuel consumed, more power is delivered for that fuel consumed. Note that below 100% throttle, peak efficiency RPM roughly scales with power demand. The above efficiency discussion assumes WOT.


So in my opinion, this debate is settled by one simple question. Are you willing to rev your engine at 4500+ RPM for short periods for maximum propulsive power? If yes, go 4.56. If not, go 4.88 or 5.13.

Note the above conversation only applies to 4.56/4.88 relative to 33" nominal tires. Substitute that with 4.88/5.13 for 35" nominal tires.


TL;DR: Y'all need to downshift more.
 
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MutantNinjaTJ

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All I know is my Jeep on 33's and running 456's with the 6 speed has zero issues with power when wheeling in all the southern Colorado mountian passes. So what is different between mine and the OP's that mine can breath just fine up in the thin air.
 

Rickyd

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What I mean is you are never gonna convince RickyD! Not tagging him bc I don’t want to read anymore of his bull.
My point is pick your ratio and be done.it will put your motor in the powerband as steels long post tries to demonstrate.when you run out of power you need to put your motor at or near peak to get the most work from it.But if you want more power you need to address the motor.

If you are talking about the nsg being worlds different then yes,you aren't going to convince me.
 

freedom_in_4low

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All I know is my Jeep on 33's and running 456's with the 6 speed has zero issues with power when wheeling in all the southern Colorado mountian passes. So what is different between mine and the OP's that mine can breath just fine up in the thin air.

Same. My nsg370/4.88/35 combo is basically the same speed vs rpm relationship and I can't think of how I could improve upon it with a different ratio.

For whatever reason my 99 TJ (Ax15) just didn't feel as strong as my 06 LJ does. I needed 3rd, sometimes 2nd gear to get the TJ over Monarch pass (sustained 7% grade at 11k') with 32/3.73. When I changed to 4.56, I was in a higher gear but I still managed about the same 35-40mph. I think that goes to steels point that the horsepower to the wheels ended up the same either way, but I didn't have to downshift as far to get into the powerband.

Now that I live at 1200', I have yet to see a place where I can't maintain the speed limit, even when it's 80. And when I took it to Silverton last year I had no trouble on any of those passes, including Slumgullion which is stupid steep.
 
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Rickyd

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Gearing is going to help solve it, because it helps put the engine into the power band better for the build.

I can tell you first hand that 4.10s vs 5.13s on 35s made a world of difference going through the mountains.
Again, "so long as gearing is within acceptable range". He asked 4.56 vs 4.88. 4.88 will give a small improvement over 4.56.

Don't take my comments to say gearing isn't important,it is. It just isn't everything
 

jjvw

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My point is pick your ratio and be done.it will put your motor in the powerband as steels long post tries to demonstrate.when you run out of power you need to put your motor at or near peak to get the most work from it.But if you want more power you need to address the motor.

If you are talking about the nsg being worlds different then yes,you aren't going to convince me.
Regears aren't inexpensive. Many of us feel it is prudent to choose wisely before spending the money.
 

Rickyd

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Regears aren't inexpensive. Many of us feel it is prudent to choose wisely before spending the money.
Nor is it rocket science. Once the matter was settled on the first page i addressed the fact its still a 4.0l..they are slugs at sea lvl