What is considered lugging the 4.0?

[MrBClark]

What do you guys consider lugging the engine in the 4.0 on the highway? I have a friend that has 3.07 gears with 31s and claims he runs 1700 rpm at 65 mph in 5th and 2200 rpm at 65 mph in 4th. That's sounds like it would lug the engine pretty bad to me. I run around 3k rpm at 75ish mph with 3.73 gears and 31s. Also, how long can the 4.0 handle these rpms on the highway? Everything gets pretty loud at those speeds.

 

[Tomcat]

I have a 4.0 auto, 3.73's with 31's. I run 2000 rpm at 65 in OD, 2500 rpm in 3rd. It doesn't seem to be lugging until I hit a steep hill, if I'm in OD I take it out till I'm over.

 

[MrBClark]

I have a 4.0 auto, 3.73's with 31's. I run 2000 rpm at 65 in OD, 2500 rpm in 3rd. It doesn't seem to be lugging until I hill a steep hill.

I have the nv3550 5 speed. It should have 3.73 gears unless the PO swapped without telling me. Rpms are high on the highway. Can the 4.0 handle higher highway rpms for a while?

 

[bromel]

I have the nv3550 5 speed. It should have 3.73 gears unless the PO swapped without telling me. Rpms are high on the highway. Can the 4.0 handle higher highway rpms for a while?

Sounds like you've been re-geared. I have 3.73 gears and 30s, and I'm around 2,500 RPM at 75 mph in 5th gear.

 

[MrBClark]

Sounds like you've been re-geared. I have 3.73 gears and 30s, and I'm around 2,500 RPM at 75 mph in 5th gear.

Is there a way to figure out my gearing without taking off the dif cover and counting? Like a mathematical formula? Also, can the 4.0 handle the high rpms on the highway for a while?

 

[xxdabroxx]

Jack up the rear axle, block the front tires and put the trans in neutral. Spin the driveshaft and count the revolutions it takes to make one full turn on the tires. That number of turns is your gear ratio.

 

[nk24]

Is there a way to figure out my gearing without taking off the dif cover and counting? Like a mathematical formula? Also, can the 4.0 handle the high rpms on the highway for a while?

It sounds like you have regeared axles. You can use the grimm jeeper tool to verify. I'm guessing you have 4.56 gears.

Also, you can run 3,000 RPM all day on the 4.0.

 

[MrBClark]

It sounds like you have regeared axles. You can use the grimm jeeper tool to verify. I'm guessing you have 4.56 gears.

Also, you can run 3,000 RPM all day on the 4.0.

And these higher gears are better right? Also, would 2200 rpm on the highway be lugging the 4.0? What about 1700?

 

[nk24]

And these higher gears are better right? Also, would 2200 rpm on the highway be lugging the 4.0? What about 1700?

It is ideal to have cruising RPM above 2,500 to avoid lugging, so 1,700 is way too low.

 

[bromel]

Is there a way to figure out my gearing without taking off the dif cover and counting? Like a mathematical formula? Also, can the 4.0 handle the high rpms on the highway for a while?

You can use this site to figure it out:

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

 

[bromel]

From my math, you should have 4.88 gears if you are doing 75 mph at 3,000 RPM with 31s in 5th gear.

 

[MrBClark]

From my math, you should have 4.88 gears if you are doing 75 mph at 3,000 RPM with 31s in 5th gear.

Yea I tried that website. Who knew there were so many versions of the nv3550. Never made it to the end of it are 4.88 gears good for larger tires? Like 33's?

 

[tworley]

3k RPM is not hurting anything.

Mine is geared for 3k at 75mph. 65 is right about 2600 RPM.

 

[Steel City 06]

Lugging is dependent upon both throttle position and engine RPM. You can run 1200 RPM without lugging at very light throttle. You can also lug at 2000+ RPM with the throttle wide open. There is no one single RPM that causes lugging.

As a very general rule of thumb, the percent throttle should be around the percent (0% at idle and 100% at peak torque) of RPM. So at 2500 RPM, 70% throttle is about the limit. At 1500 RPM, you want less than 35% throttle. (Even that might lug.) Full throttle should be done at or above the RPM for peak torque (~3200 RPM).

Generally, riding the threshold of not lugging results in the best fuel economy.

At a given road speed, the torque at the wheels will be maximized when engine RPMs are at or near peak horsepower (~4,600 RPM). Generally this means shifting at redline. (This will result in a loss of fuel economy.) So if you need to climb a hill at the fastest possible speed, downshift until you get as close to 4600 RPM (without redlining) as possible.

 

[Goatman]

Step on the skinny pedal. If you immediately start to accelerate you aren't lugging. If it just makes a low aaaaaagh sound then you are definitely lugging.

 

[Jerry Bransford]

And these higher gears are better right? Also, would 2200 rpm on the highway be lugging the 4.0? What about 1700?
[/QUOTE

What do you guys consider lugging the engine in the 4.0 on the highway? I have a friend that has 3.07 gears with 31s and claims he runs 1700 rpm at 65 mph in 5th and 2200 rpm at 65 mph in 4th. That's sounds like it would lug the engine pretty bad to me. I run around 3k rpm at 75ish mph with 3.73 gears and 31s. Also, how long can the 4.0 handle these rpms on the highway? Everything gets pretty loud at those speeds.

Don't confuse the low rpms a standard car with its small tires runs fine at with the rpms a boxy non-aerodynamic Wrangler with big Jeep-size tires requires. 1700 is DEFINITELY lugging it badly and 2200 is lugging it too. And low rpms doesn't necessarily mean better mpg either. Most people consider 2500 rpms appropriate for smaller tires with bigger tires like my 35's requiring 2700 to run well. I bought my second TJ used and it was geared to only produce 2200-2300 with 35" tires and it was lugging badly with bad <12 mpg. I regeared with 5.38 gears (mine is the 4-speed automatic) to get the rpms up to around 2650 at 70 mph (which is still a tad low for 35's) and the Jeep just ran and felt better all the way around, not to mention the mpg went up from <12 mpg to over 14 mpg.

The biggest thing to learn about our Wranglers is #1 the engine is definitely happy all day even at 3000 rpms and that the low rpms of a car are in no way an indication of appropriate rpms for a Wrangler with its typically big tires, weight (even though it may look light it's not), and the aerodynamics of a barn door.

 

[Grant Lasson]

Lugging is dependent upon both throttle position and engine RPM... There is no one single RPM that causes lugging.

As a very general rule of thumb, the percent throttle should be around the percent (0% at idle and 100% at peak torque) of RPM.
Generally, riding the threshold of not lugging results in the best fuel economy.

Super helpful content. I find these "lugging" threads to be oversimplified most of the time. I have a manual transmission so my first question is what gear am I in? First and second gears are very different for lugging than 3, 4 or 5. Am I going uphill or downhill or flat? I can cruise at 2K RPM on a flat freeway just fine in 5th gear. That's riding the lugging line but I find gets better mileage.

I tried running consistently at 2800-3500 RPM on the freeway. Getting up hills is much improved. The tradeoff was much worse gas mileage. I'm going to use 4th gear quicker and more frequently in these conditions than I have in the past but overall I'm sticking with the lower cruising RPMs.

 

[WallyWest]

Yea I tried that website. Who knew there were so many versions of the nv3550. Never made it to the end of it are 4.88 gears good for larger tires? Like 33's?

Been researching this myself and yeah, 4.88 gears with the nv3550 and the 4.0 is about ideal for 33 inch tires.

 

[B00mb00m]

I just started running OD off more this past gas tank fill. I have been doing mostly 3K going ~60 (5.13 + BL'd 37s). Unfortunately my mileage actually went down to 11, i was at 12.5, though ive also had new gears put in front a month ago. Not sure if that had some effect.

Also wonderin when I should check if my cats are good. I'm at 90K but not throwing any codes.

 

[Davidtj]

Just recently re geared so give you what I found out. When I bought my Jeep it had 31’s and 3:07 gearing while it was ok ( I thought so) 5 gear was useless on highway After I re geared to 4:11 I immediately realized I was probably lugging all the time , because I have a manual I can control shift points. The motor revs up while driving at least twice as fast as previously. All this according to butt Dino