Re-gearing: Are 4.10's Too Big?

[Darky]

What Milford is saying is that regearing for tire size is the right way to go, going slightly deeper is ok...but trying to make up for weight and lack of aerodynamics by spinning the engine to the moon on the highway, and trying to fool us into thinking that you're suddenly pulling wheelies and getting better fuel mileage than stock is a bit hard to swallow. I know he's tired and frustrated with the same thing I am here...the constant preaching to run tons of gearing with little tires.

I have never had a properly running 4.0 HO/AW4 accelerate from a stop better with too much gearing vs. not enough. That's because the 4.0 is not a quick or high revving engine, and gearing it so that it needs to rev quickly and high to row through the gears (in stock form) does not aid in acceleration for this particular engine. I've had plenty of them, and I've regeared hundreds for paying customers.

I've also had plenty of Samurai's...guess which one has given me the best acceleration and fuel mileage? Yup, the one with factory gearing and an engine upgrade on 31's (that's the same tire increase as going from stock to 32-33" on an XJ). All the ones I geared to the moon accelerated better than stock geared ones with bigger tires(but not better than this current one), but just screamed at 65 with my foot on the floor...huh, I thought gearing as deep as possible was the wonder cure, and would supply me with tons of new found "power"?

Guess what I did to get better acceleration and better fuel mileage out of my Dodge/Cummins? Added a power tuner and increased tire size to 35" to slow the rpm's on the highway...but based on the advice here, I should have geared it to 4.88 and just let it scream:nosmile:

Guess what I did to drop my fuel mileage in my '01 XJ from 18+ to barely 14...added 33's and geared to 4.56. Now it doesn't accelerate any better (but it sure makes more noise and shifts quicker), revs way higher than I want it to on the highway (4.10's would have made me much happier, but I had these) making the fuel mileage suck, the driveline sing and vibe, and it still downshifts if I'm too aggressive with the right foot trying to accelerate (wonder where my magic "more power" went), yet the engine ends up revving too high when it does downshift to actually do anything productive.

A good mix of regearing the diffs for tire size for the road, regearing the transfer case for off road, and adding some power is the "right way" to go...but to each their own. I totally get gearing super deep for a rig that is a toy...for wheeling...not a DD that sees lots of road/highway time though.

There is a happy medium, and gearing super deep doesn't make up for the need for more power efficiency from the engine.

You know the sure sign of someone who's wrong? Throwing completely unrelated stories at you. A 53hp Samurai (if it's in perfect condition) that's already geared to the moon and a turbo diesel pickup that's meant to be geared super tall and puts out 400+lb-ft at idle do not make good comparisons with an J the puts out max power/torque in the 2500-3000 rpm range.

 

[ktm racer 419]

Well, you are awesome...it stands to reason that your Jeep would be too.

How could I possibly compete with the experience that 10,000+ posts gives youaperwork

pixie dust, not experience.

 

[NorCalChris]

What Milford is saying is that regearing for tire size is the right way to go, going slightly deeper is ok...but trying to make up for weight and lack of aerodynamics by spinning the engine to the moon on the highway, and trying to fool us into thinking that you're suddenly pulling wheelies and getting better fuel mileage than stock is a bit hard to swallow. I know he's tired and frustrated with the same thing I am here...the constant preaching to run tons of gearing with little tires.

I have never had a properly running 4.0 HO/AW4 accelerate from a stop better with too much gearing vs. not enough. That's because the 4.0 is not a quick or high revving engine, and gearing it so that it needs to rev quickly and high to row through the gears (in stock form) does not aid in acceleration for this particular engine. I've had plenty of them, and I've regeared hundreds for paying customers.

I've also had plenty of Samurai's...guess which one has given me the best acceleration and fuel mileage? Yup, the one with factory gearing and an engine upgrade on 31's (that's the same tire increase as going from stock to 32-33" on an XJ). All the ones I geared to the moon accelerated better than stock geared ones with bigger tires(but not better than this current one), but just screamed at 65 with my foot on the floor...huh, I thought gearing as deep as possible was the wonder cure, and would supply me with tons of new found "power"?



Guess what I did to drop my fuel mileage in my '01 XJ from 18+ to barely 14...added 33's and geared to 4.56. Now it doesn't accelerate any better (but it sure makes more noise and shifts quicker), revs way higher than I want it to on the highway (4.10's would have made me much happier, but I had these) making the fuel mileage suck, the driveline sing and vibe, and it still downshifts if I'm too aggressive with the right foot trying to accelerate (wonder where my magic "more power" went), yet the engine ends up revving too high when it does downshift to actually do anything productive.

A good mix of regearing the diffs for tire size for the road, regearing the transfer case for off road, and adding some power is the "right way" to go...but to each their own. I totally get gearing super deep for a rig that is a toy...for wheeling...not a DD that sees lots of road/highway time though.

There is a happy medium, and gearing super deep doesn't make up for the need for more power efficiency from the engine.

In your edumacated opinion what gears would you run on a stock 4.0 of any year with an auto? and with a manual?
31-?
32-?
33-?
35-?

I'm sorry if you think 3k rpm is spinning it to the moon. I sure don't think it is.

 

[NorCalChris]

pixie dust, not experience.

Can I have some of that pixie dust?

 

[X E Ryder]

Can I have some of that pixie dust?

Please get some for me. My valvetrain is getting noisy and I don't have time to deal with it.

 

[bobnoxious]

Dundys XJ with 4.10s and 35s would beat my XJ with 4.88s and 35s.

Blasphemy!

 

[bobnoxious]

You know the sure sign of someone who's wrong? Throwing completely unrelated stories at you. A 53hp Samurai (if it's in perfect condition) that's already geared to the moon and a turbo diesel pickup that's meant to be geared super tall and puts out 400+lb-ft at idle do not make good comparisons with an J the puts out max power/torque in the 2500-3000 rpm range.

It's completely relevant...it's an automobile, and physics. Don't be all pissed off just because I use valid examples that may shoot holes in your finely laid ideas.


PS: max HP rating on the 5.9 Cummins is at 2900 RPM:looser:

 

[bobnoxious]

In your edumacated opinion what gears would you run on a stock 4.0 of any year with an auto? and with a manual?
31-?
32-?
33-?
35-?

I'm sorry if you think 3k rpm is spinning it to the moon. I sure don't think it is.

Why are you "sorry"? Just because I don't confuse max TQ rpm with max efficiency rpm? Because I know that drastic overgearing doesn't equal power and economy...that it doesn't make up for extra weight and lost aerodynamics? That I don't think to myself "OK, I need this much gearing to make up for the tires...now this much more so I have more power for the extra weight...now I need just some extra because I want more power and economy than stock"? It doesn't work that way:shhh:

You can buzz your engine on the highway at whatever RPM you like...have a ball.

I'm just sharing my personal experience...forgive me if it doesn't match up with yours.

At no point did I say anybody was wrong to overgear their rig...but it's not the wonder power/economy adder that some make it out to be.

 

[XJEEPER]

Man up and give the engine a power upgrade.

Bob, what specific power upgrades do you suggest to the 4.0L that will produce the same net result as lowering the gear ratio (numerically higher) to offset larger tires?

 

[bobnoxious]

Bob, what specific power upgrades do you suggest to the 4.0L that will produce the same net result as lowering the gear ratio (numerically higher) to offset larger tires?

There is no magic gear ratio that will make an XJ pull like it has 250 HP...that's my point.

 

[FlexdXJ]

I'm doing 4.10's and going with 32's...or should i go 6.79's with lawnmower tires?

 

[Darky]

It's completely relevant...it's an automobile, and physics. Don't be all pissed off just because I use valid examples that may shoot holes in your finely laid ideas.


PS: max HP rating on the 5.9 Cummins is at 2900 RPM:looser:

And where is the max torque rating, since that was what I was referring to? I guarantee you that a Cummins puts out more torque at low rpm than an XJ could ever hope to.

Funny story: engines make differing levels of power at different rpms, hence why there is no one gear ratio that works for all vehicles. Samurais come geared very low from the factory. I know my old Tracker, descendant of the Samurai, was geared somewhere around 4.5x in order to spin 205/75R15s.

Why are you "sorry"? Just because I don't confuse max TQ rpm with max efficiency rpm? Because I know that drastic overgearing doesn't equal power and economy...that it doesn't make up for extra weight and lost aerodynamics? That I don't think to myself "OK, I need this much gearing to make up for the tires...now this much more so I have more power for the extra weight...now I need just some extra because I want more power and economy than stock"? It doesn't work that way:shhh:

You can buzz your engine on the highway at whatever RPM you like...have a ball.

I'm just sharing my personal experience...forgive me if it doesn't match up with yours.

At no point did I say anybody was wrong to overgear their rig...but it's not the wonder power/economy adder that some make it out to be.

Two questions: Who said it would improve economy over stock? The highest I've heard quoted was 17mpg. I don't know about you, but I was getting 20+ hwy stock.

What I think is being misunderstood is that what we, or at least, I am saying is that gearing just to get back to factory rpms is only part of the picture. Physics dictates that even if all else is equal (cD, overall weight, etc) the fact that the tire's weight is further from the centerline will still require more power to overcome. Gearing a bit deeper than stock will help overcome that, bringing you closer to stock performance. No one is claiming that over gearing will make your Jeep a hotrod.

 

[XGarfX]

Wow this thread got out of hand.... I think the point that people that have overgeared a little bit for larger heavier tires are trying to make here is this, going a tad bit deeper then what the "on the dot" charts say to go to won't hurt you. Lugging the motor around puts much more wear on it then having it spin 300rpms higher then the next higher gear set....

How about this to make it fair, those running gears that are supposedly to deep or shallow for their tires post their hand calculated, replaced speedo gear MPG's?

I'll start....

99 xj, 33x12.50 KM2s, 4.5 inch RK 3 link..... 4.88s.
Town mpg-16
HWY mpg- 18 (highest recorded was 21)

 

[cheapcherokee93]

i think theres going to be too many variables for this idea to work, like engine mods and driving style, but whatever i'll bite


88 MJ auto, 235/75 r15 3" lift..... 4.10
100% city- 13
50/50- 15
100% highway- 19

as a side note, i have a mild cam, pacesetter headers, and bosch type 3 injectors.

 

[MoparManiac]

XXXX this thread.

Lugging the motor around puts much more wear on it then having it spin 300rpms higher then the next higher gear set....

No one is saying to lug the engine at 1500 rpms.

I don't know about you, but my personally experience was my buddy's 2001 XJ with 4.10s and 35s would beat my '92 XJ with 4.88s and 35s off the line everytime. My XJ was blowing through gears too fast.

On the highway sure his 4.10s were not enough, but no one is saying that they are enough for 35s.

When I had 4.88s and 33s it was too much gearing for the highway. Did I go back and regear them to 4.10s? No. I just did 65 instead of how I normally liked to go 75 to keep up with traffic. You can tell me all you want that the 4.0 "likes" spinning at 2800, but it did not feel like it. It felt like it was hanging in the gear.

 

[XJLI]

And my 93 sang at 2800. Every motor is different bc half of us have no idea wtf the first 150k was like on our jeeps.

 

[MoparManiac]

And my 93 sang at 2800. Every motor is different bc half of us have no idea wtf the first 150k was like on our jeeps.

What do you mean "sang" at 2800?

My whole point was that it felt like the engine had too light of a load behind it, and was just wasting fuel being revved up that high.

I never measured fuel consumption. I do know that with 4.88s and 35s I averaged 15 city/highway with a corrected speedo. On a full out highway trip, I squeezed out 20 on a non-hill section.

I was sitting right at 2500 at 70-75. Working the engine right where it felt most efficient.

And I'd actually pulled the pan and valve cover off my engine, and it looked mint inside

And Sam's XJ is an outlier because he had almost 300k on his :laugh:

 

[zachandandy]

I can't believe this thread has gone this far and nobody has mentioned it yet, but what's the red category of all those gearing charts say? POWER! Gearing isn't the right way to combat added weight and rolling resistance? Why does the towing package almost always include lower gears? Why put 4.10's in the 4 bangers? Maybe gears do make up for a lack of power? Comparing a 5.9 cummins that is detuned from the factory to an xj? That programmer added the entire power output of a 4.0! Guess there are 2 guys here on naxja that know more than all the real world experience, gearing manufacturers, and oems combined? For a DD I'd lean toward the higher end of the green part of the chart, for a jeep that gets wheeled, go for the red zone. Auto with OD I'd go 1 size lower.

 

[ktm racer 419]

And Sam's XJ is an outlier because he had almost 300k on his :laugh:

i was bored one day and swapped out the 225k mile motor with a 150k mile motor though.

 

[Darky]

XXXX this thread.



No one is saying to lug the engine at 1500 rpms.

I don't know about you, but my personally experience was my buddy's 2001 XJ with 4.10s and 35s would beat my '92 XJ with 4.88s and 35s off the line everytime. My XJ was blowing through gears too fast.

On the highway sure his 4.10s were not enough, but no one is saying that they are enough for 35s.

When I had 4.88s and 33s it was too much gearing for the highway. Did I go back and regear them to 4.10s? No. I just did 65 instead of how I normally liked to go 75 to keep up with traffic. You can tell me all you want that the 4.0 "likes" spinning at 2800, but it did not feel like it. It felt like it was hanging in the gear.

I concur with the first statement.

My engine feels perfectly happy cruisin 70 with 33s and 4.88s. Well, normally...I let my transmission run the same old fluid for too long and now I have a slipping clutch.

I can't believe this thread has gone this far and nobody has mentioned it yet, but what's the red category of all those gearing charts say? POWER! Gearing isn't the right way to combat added weight and rolling resistance? Why does the towing package almost always include lower gears? Why put 4.10's in the 4 bangers? Maybe gears do make up for a lack of power? Comparing a 5.9 cummins that is detuned from the factory to an xj? That programmer added the entire power output of a 4.0! Guess there are 2 guys here on naxja that know more than all the real world experience, gearing manufacturers, and oems combined? For a DD I'd lean toward the higher end of the green part of the chart, for a jeep that gets wheeled, go for the red zone. Auto with OD I'd go 1 size lower.

I thought it, just didn't type it. I did hint at it with the comparison to what a Samurai is likely geared from the factory based on high my Tracker was geared.