4.0L Performance Help

[TJ John]

Here's the problem I'm having. I have a 2000 TJ 4.0L 5 speed Manual 115,000 miles. I added 33" tires and 4:10 gears and at 55mph my RPM are at 1900. I don't remember what they are at 65mph, but at 65mph on the interstate going up a hill I always have to down shift from 5th to 4th or I won't make it up i'll just keep slowing down.
The engine runs great! purrs like a kitten! I've tuned it up, which means new plugs and an air cleaner there's really not much to them.
But come on it's only a Jeep there's not much weight there. I shouldn't have to down shift at that speed. I Didn't have to down shift when it was stock with stock tires and 3:07 gears.

So, are the 33" tires too big for the 4:10 gears?
Is there anything I can do to get more HP & TQ short of an engine rebuild?
Has anyone else experienced that with their Jeep after doing these mods?

I looked on this tread but couldn't find anything to help.
TJ Frequently Asked Questions

Jeep 4.0 Myth Busting (What Mods Really Equal Power Gains?)

 

[Kevin E]

Your gear ratio should be 4.56 with your tires and tranny setup. How much grade are you talking on "hills"? I have the same as you and yes it's very possible you will need to downshift. Not many hills where I live so the 4.10s do good here

 

[Jerry Bransford]

Yep, the 4.10 gearing is not enough for 33's which is why I always recommend 4.56 with your configuration. Didn't we discuss ratios before you regeared to 4.10 for those 33's?

I had the 4.10/33" tire combination for a short while and I didn't like it at all... not even when I was in flat areas.

 

[TJ John]

Yep, the 4.10 gearing is not enough for 33's which is why I always recommend 4.56 with your configuration. Didn't we discuss ratios before you regeared to 4.10 for those 33's?

No. I didn't know about this forum at that time. I had all this work done in the spring of 2016. The 4x4 place wanted to install 4:88's they never suggested 4:56. I wanted to still be able to drive it on the Hwy. I pretty new to the 4x4 world and I was thinking of when I would race with my 72 Chevelle and 4:10's sounded like alot.

 

[Fouledplugs]

Bottom line gearing helps the 4.0L when adding big tires or heavy axles.

As great as the 4.0L is it falls on its face when compared to others. Most engine builders will tell you a properly tuned engine should make 1 to 1.5 HP per Cubic Inch. Unfortunately the factory 4.0L doesn't support this idea. nor does it's PCM open for fuel and air modifications which I think is it's greatest downfall.

It is my opinion (I know, I know) that a good intake, port and polished Edelbrock Alum head, and full exhaust will make noticeable improvements. A wide band, aftermarket PCM piggyback tuner, and engine dyno tune is where are going to make any real world results.

But nonetheless the 4.0 is very reliable and predictable. Correct gearing will be your best friend.

 

[TJ John]

Your gear ratio should be 4.56 with your tires and tranny setup. How much grade are you talking on "hills"? I have the same as you and yes it's very possible you will need to downshift. Not many hills where I live so the 4.10s do good here

Not a lot of hills where I use to live in MN but now I live in MO off of I-44. A lot more hills down here.
Well, I don't have the money to regear it. I was hoping there was something I could do to free up the engine, unlock some caged HR from the factory setup.

 

[TJ John]

Bottom line gearing helps the 4.0L when adding big tires or heavy axles.

As great as the 4.0L is it falls on its face when compared to others. Most engine builders will tell you a properly tuned engine should make 1 to 1.5 HP per Cubic Inch. Unfortunately the factory 4.0L doesn't support this idea. nor does it's PCM open for fuel and air modifications which I think is it's greatest downfall.

It is my opinion (I know, I know) that a good intake, port and polished Edelbrock Alum head, and full exhaust will make noticeable improvements. A wide band, aftermarket PCM piggyback tuner, and engine dyno tune is where are going to make any real world results.

But nonetheless the 4.0 is very reliable and predictable. Correct gearing will be your best friend.

Well crap!! Thanks for your input, I guess I'll just have to keep down shifting.

 

[Jerry Bransford]

I was hoping there was something I could do to free up the engine, unlock some caged HR from the factory setup.

Nope, that's why the 4.0 was discontinued in favor of the V6... they had run out of things to do to it to improve its performance or MPG or comply with the increasingly tougher fed and state smog laws. Besides the 4.0L wasn't designed for HP, it was designed for low-end torque. Inline engines develop more torque, V6 and V8 engines are better where HP is concerned.

Throttle body spacers won't help, nor will a larger diameter TB. Not a Tornado, not E-3 spark plugs. The only thing that will help short of a supercharger is to regear the axles to a lower ratio or drop the tire size down one.

 

[Fouledplugs]

Well crap!! Thanks for your input, I guess I'll just have to keep down shifting.

Or it depends on how far you are willing to take it as far as upgrades are concerned. You could find a junkyard 5.3 LS and start doing your research. I was able to find one for less than 900 complete with harness and trans. They are everywhere and the junk yards have millions of them, thanks to GM putting them in practically everything.

Let it be a long term goal. focus on the gearing and keep wheeling happily.

 

[TJ John]

Nope, that's why the 4.0 was discontinued in favor of the V6... they had run out of things to do to it to improve its performance or MPG. Besides the 4.0L wasn't designed for HP, it was designed for low-end torque. Inline engines develop more torque, V6 and V8 engines are better where HP is concerned.

Throttle body spacers won't help, nor will a larger diameter TB. Not a Tornado, not E-3 spark plugs. The only thing that will help short of a supercharger is to regear the axles to a lower ratio or drop the tire size down one.

So I guess if I ever decide to go to 35's I would be better off with 4:88's

 

[Jerry Bransford]

So I guess if I ever decide to go to 35's I would be better off with 4:88's

Yes for sure.

 

[Fouledplugs]

Nope, that's why the 4.0 was discontinued in favor of the V6... they had run out of things to do to it to improve its performance or MPG or comply with the increasingly tougher fed and state smog laws. Besides the 4.0L wasn't designed for HP, it was designed for low-end torque. Inline engines develop more torque, V6 and V8 engines are better where HP is concerned.

Throttle body spacers won't help, nor will a larger diameter TB. Not a Tornado, not E-3 spark plugs. The only thing that will help short of a supercharger is to regear the axles to a lower ratio or drop the tire size down one.

Yes, sad to see the 4.0L go.

 

[TJ John]

I was looking at Hypertech to get some more performance but that's a lot of money for 5 to 10 more HP!

 

[Fouledplugs]

I was looking at Hypertech to get some more performance but that's a lot of money for 5 to 10 more HP!

Skip it and spend it on gearing, axles, lockers, or something else that will need to be purchased.

If you really want to talk to EXPERTS with experience on the 4.0L contact Hesco performance, 505 performance, or start researching online more about built 4.0L's. Chances are that you will find you're spending a lot of money and getting less return if you were to swap it.

 

[Jerry Bransford]

I was looking at Hypertech to get some more performance but that's a lot of money for 5 to 10 more HP!

Again, things like that won't help. The Hypertech will only help slightly once the engine's rpms are at near redline and the throttle is wide open. It will do nothing and can do nothing to improve the low-end torque lost by being undergeared.

 

[Chris]

I'll echo what's been said already, you really should have 4.56 gears, it would help a lot.

In addition to that, remember that the 4.0 isn't a high horsepower engine, it mostly has just high torque. Torque is what gets you there, horsepower is what keeps you there... That's what I always say.

Our Wranglers are heavy (they are) and they have piss poor aerodynamics.

A Hypertech is nothing but a scam. Things like that won't work on our 4.0s. If you have $2500 to drop, I highly recommend a supercharger (I own one, so I can vouch for it): http://www.boostedtech.com

It bolts right on, and believe me when I say your 4.0 will be FAST. You'll have no trouble on the highway or hills.

 

[TJ John]

Thanks for everyones help. I guess I'll stick with what I have until it's time to repair/replace. It sounds like gears will give me the biggest return on my money.
Does anyone know what the RPM sweet spot is for HP/TQ on the 4.0L?

 

[Kevin E]

I'll echo what's been said already, you really should have 4.56 gears, it would help a lot.

In addition to that, remember that the 4.0 isn't a high horsepower engine, it mostly has just high torque. Torque is what gets you there, horsepower is what keeps you there... That's what I always say.

Our Wranglers are heavy (they are) and they have piss poor aerodynamics.

A Hypertech is nothing but a scam. Things like that won't work on our 4.0s. If you have $2500 to drop, I highly recommend a supercharger (I own one, so I can vouch for it): http://www.boostedtech.com

It bolts right on, and believe me when I say your 4.0 will be FAST. You'll have no trouble on the highway or hills.

I'm saving for one!

 

[TJ John]

I'll echo what's been said already, you really should have 4.56 gears, it would help a lot.

In addition to that, remember that the 4.0 isn't a high horsepower engine, it mostly has just high torque. Torque is what gets you there, horsepower is what keeps you there... That's what I always say.

Our Wranglers are heavy (they are) and they have piss poor aerodynamics.

A Hypertech is nothing but a scam. Things like that won't work on our 4.0s. If you have $2500 to drop, I highly recommend a supercharger (I own one, so I can vouch for it): http://www.boostedtech.com

It bolts right on, and believe me when I say your 4.0 will be FAST. You'll have no trouble on the highway or hills.

WOW! $2700. now.

 

[Shane Mckinley]

I would sell the 33s and go to a 32


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