Power upgrades.. what to do?

[BugNuker]

Hello all.
I'm kinda new here. Been lurking for a while.
I have a 2002 Liberty, Limited, fully loaded, blah blah.
I've done many modifications to it, to the tune of electronics.
I am wanting to do some power upgrades to it here soon.
I've read some things on throttle bodies, some good, some bad.
I was thinking about a cat back exhaust system.

What are some upgrades I can do to my 3.7L liberty motor/drive train?

Thanks for your help!

 

[ridenby]

The stock exhaust is 2.5in. mandrel bent,don't see much improvement there. The muffler is a heavy,restrictive deal.

 

[LibertyTC]

Locker rear and 4:10's front and rear...whoh..bye bye..

 

[BugNuker]

Locker rear and 4:10's front and rear...whoh..bye bye..

Haha. I only get 16 MPG as it is!

 

[tommudd]

Depending on the size of your tires 4.10s will help with mileage. I've been using my 6X10 enclosed trailer to move to my new place, with it fully loaded I can average 16 MPGs in traffic and out the road.

 

[04Liberty]

2005+ have slightly hotter cam timing, you can swap cams or even get a set reground. Depending on the p/n of your PCM you can even get custom tuning via SCT tuner (I have done this). Even what they call "canned" tuning (a standard 87, 91 or 91 tow) is very noticeable on a completely stock vehicle.

 

[J-Thompson]

Haha. I only get 16 MPG as it is!

If I were you I would try to fix this problem rather than look for "more power"
our KJ would get 18 average with 245/75 LR-E MTR's and 3.73's
had I put in 4.10's we could have gotten 20+ easily
if you are stock tire hight and getting 16 you have issues ,my TJ with 33's
and 3.73 gears with no OD gets 15

 

[BugNuker]

If I were you I would try to fix this problem rather than look for "more power"
our KJ would get 18 average with 245/75 LR-E MTR's and 3.73's
had I put in 4.10's we could have gotten 20+ easily
if you are stock tire hight and getting 16 you have issues ,my TJ with 33's
and 3.73 gears with no OD gets 15

I have a 2.5 inch lift with bigger tires.
Jeep says 16.4 avg MPG, but the calculation is off due to the bigger tires, so I might be getting around 17-18 city. I have been able to get around 22 highway.

What gear ratio is stock in the liberty?

 

[HoosierJeeper]

3.73 with the CRD and 3.7, 4:10 with the 4 popper...

 

[BugNuker]

Ok guys, I have what will seem to be a stupid question.

If I put 4:10 gears in, how does this make gas millage better?

If I understand correctly (granted, this is with my classic muscle car), higher gears = faster acceleration, but higher RPM's, and, in general, worse gas mileage, due to all the fun you are having.

How does putting 4:10 in my Liberty make me have better gas mileage?

Thanks

 

[tjkj2002]

Ok guys, I have what will seem to be a stupid question.

If I put 4:10 gears in, how does this make gas millage better?

If I understand correctly (granted, this is with my classic muscle car), higher gears = faster acceleration, but higher RPM's, and, in general, worse gas mileage, due to all the fun you are having.

How does putting 4:10 in my Liberty make me have better gas mileage?

Thanks

This is why........................

I have a 2.5 inch lift with bigger tires.

 

[05kj6spd]

The 4.10 gears will give the drivetrain a greater mechanical advantage for turning the tires. In short it will take less effort for you engine to get the bigger tires rolling allowing you to use less throttle to pull out and pick up speed. Yes it will mean higher RPMs and possibly extra gas consumption at higher speeds but the benefits on low end usually more then make up for that.

 

[tjkj2002]

The 4.10 gears will give the drivetrain a greater mechanical advantage for turning the tires. In short it will take less effort for you engine to get the bigger tires rolling allowing you to use less throttle to pull out and pick up speed. Yes it will mean higher RPMs and possibly extra gas consumption at higher speeds but the benefits on low end usually more then make up for that.

Actually will return the rpm's at cruising speed back into OEM specs,closer to peak torque where your KJ will get the best mpg's and performance.

 

[05kj6spd]

Actually will return the rpm's at cruising speed back into OEM specs,closer to peak torque where your KJ will get the best mpg's and performance.

I still say the most gain is consumption off the line. If it's just a matter of getting the rpms the same he would only have to cruise fast then before. Bottom line is....if he was doing 60 MPH with the engine reving at 2300 RPM then he may now be going 65 MPH with the engine reving 2300 RPM. The most lost of gas mileage when installing larger tires is the extra "drag" created by the tires. This is the weight of the larger tires more friction contact between the tire and the road...from wider tires and even taller tires. This translates to more energy required to get the tires moving from a stop meaning more gas is used to supply this energy. Offsetting it with the mechanical advantage of gearing can get back some of that mileage.

 

[J-Thompson]

I still say the most gain is consumption off the line. If it's just a matter of getting the rpms the same he would only have to cruise fast then before. Bottom line is....if he was doing 60 MPH with the engine reving at 2300 RPM then he may now be going 65 MPH with the engine reving 2300 RPM. The most lost of gas mileage when installing larger tires is the extra "drag" created by the tires. This is the weight of the larger tires more friction contact between the tire and the road...from wider tires and even taller tires. This translates to more energy required to get the tires moving from a stop meaning more gas is used to supply this energy. Offsetting it with the mechanical advantage of gearing can get back some of that mileage.

"you have much to learn my young padiwan"

gearing effects it at ALL speeds
and heavier and wider has no effect on the final drive
taller does
taller = less revs per mile
less revs per mile = less engine RPM
Less engine RPM = less power
thus your engine is working harder and when an engine works harder it burns more fuel
facts of life

 

[05kj6spd]

"you have much to learn my young padiwan"

gearing effects it at ALL speeds
and heavier and wider has no effect on the final drive
taller does
taller = less revs per mile
less revs per mile = less engine RPM
Less engine RPM = less power
thus your engine is working harder and when an engine works harder it burns more fuel
facts of life

wow if you think heavier and wider doesn't affect it then you are as misguided as TJKJ. Less rpm equals less power.....only so much and we are talking only a few less. They all have a factor to play and you can't ingore the others. Weight of tire and rim (why so many use aluminum rims), aggressiveness of tread design, type of rubber used to make tire, foot print of tire, these things all matter. Don't believe me go air down to 8 pounds and drive and let me know. By your logic you tire will be shorter and thus your mileage will go up. But according to me you tire will flatten on the bottom putting more rubber to the road causing "drag" also known as traction and will cause your mileage to drop. After doing that super inflate them to 65 pounds so they bulge and you only ride on the middle most section. This will make your tire very tall and MPG go in the toilet by your logic. I say you will see a big increase in MPG over 8 pounds, it will ride like crap and you will wear out the middle of your tires.

Simply put the guy asked a question which people thought was too dumb to answer so they put smart aleck comments up. I answered with what should be common knowledge among gear heads and you guys come back with this bull. Oh and if wieght of tires doesn't make a difference pulling out then why does it stopping......and don't say it doesn't cause you wear out a set of pads a lot quicker with 35's on steel rims then 30's and aluminum.

 

[tjkj2002]

wow if you think heavier and wider doesn't affect it then you are as misguided as TJKJ. Less rpm equals less power.....only so much and we are talking only a few less. They all have a factor to play and you can't ingore the others. Weight of tire and rim (why so many use aluminum rims), aggressiveness of tread design, type of rubber used to make tire, foot print of tire, these things all matter. Don't believe me go air down to 8 pounds and drive and let me know. By your logic you tire will be shorter and thus your mileage will go up. But according to me you tire will flatten on the bottom putting more rubber to the road causing "drag" also known as traction and will cause your mileage to drop. After doing that super inflate them to 65 pounds so they bulge and you only ride on the middle most section. This will make your tire very tall and MPG go in the toilet by your logic. I say you will see a big increase in MPG over 8 pounds, it will ride like crap and you will wear out the middle of your tires.

Simply put the guy asked a question which people thought was too dumb to answer so they put smart aleck comments up. I answered with what should be common knowledge among gear heads and you guys come back with this bull. Oh and if wieght of tires doesn't make a difference pulling out then why does it stopping......and don't say it doesn't cause you wear out a set of pads a lot quicker with 35's on steel rims then 30's and aluminum.

Your tire theory and air pressure is effectively changing the final drive ratio but the friction plays the biggest role as under-inflating/over-inflating will only change your tire height by not that much.Plus you actually need to look at the engines power curve,the 3.7 does not make 210hp/235lbs-ft or torque at idle through 6000rpm's.It varies and those are peak #'s,peak hp is made over 4000rpm's along with peak torque,the closer to that peak the better mpg's you will get.Just throwing #'s out there if your pulling 2000rpm's with 3.73's and 31" tires at 65mph your looking at about 160hp range,with 4.10's and the same 31" tires at 65mph you will be turning about 2400rpm's with 180hp.

Oh and I have actual experiance,my KJ has the same feel from a dead stop when I had 32"(265/75R16's) tires and 4.10's and now I have 35x13.50x15 tires with 5.13 gears.I also have the same stopping power,but then again I also upgraded the brakes from OE KJ disc/drums to Ford F150 fronts and '96 Explorer rear disc's,but then again lower gears help acceleration but have nothing to do with braking.

 

[Ry' N Jen]

You want to maximize power and get better fuel economy?
Carry less crap in the vehicle to start!
Then you can go for a reworked throttle body, tuning chip's, freer flowing, less restrictive
exhaust components (ie. muffler, headers) Cold air intake.
Re gear to 4:10's
Drive the speed limit.

Our lifted Rig with 245-75-16 M/T tires, winch, fully loaded with recovery gear, camping equipment, food booze, weed, etc., we still got 23 miles per gallon on the freeway last time out!
(Once we even got 25 mpg with an unloaded KJ driving like a total suck, old man!)

I'm about to go the whole 9 yards and do all the aforementioned mods to get whatever performance I can get out of the 3.7 litre.
If our KJ gets 1-2 mpg more awesome! Great!
If not, I don't really give a flying F:favorites68:CK at a rolling doughnut!

So...
If 22-23 mpg isn't good enough for you, trade it in and go buy a Toyota Prius!:happy175:

 

[J-Thompson]

wow if you think heavier and wider doesn't affect it then you are as misguided as TJKJ. Less rpm equals less power.....only so much and we are talking only a few less. They all have a factor to play and you can't ingore the others. Weight of tire and rim (why so many use aluminum rims), aggressiveness of tread design, type of rubber used to make tire, foot print of tire, these things all matter. Don't believe me go air down to 8 pounds and drive and let me know. By your logic you tire will be shorter and thus your mileage will go up. But according to me you tire will flatten on the bottom putting more rubber to the road causing "drag" also known as traction and will cause your mileage to drop. After doing that super inflate them to 65 pounds so they bulge and you only ride on the middle most section. This will make your tire very tall and MPG go in the toilet by your logic. I say you will see a big increase in MPG over 8 pounds, it will ride like crap and you will wear out the middle of your tires.

Simply put the guy asked a question which people thought was too dumb to answer so they put smart aleck comments up. I answered with what should be common knowledge among gear heads and you guys come back with this bull. Oh and if wieght of tires doesn't make a difference pulling out then why does it stopping......and don't say it doesn't cause you wear out a set of pads a lot quicker with 35's on steel rims then 30's and aluminum.

let me simplify it
if you are trying to remove a large bolt that is stuck which will be easier
the ratchet and socket or the ratchet and socket with a 2 foot pipe on the ratchet?
gearing in any thing works the same
the axle shaft is the socket and the tire tread is the handle of the ratchet
as the distance from the center gets greater the force applied or required to move it gets greater
yes heavier and wider is harder to move but they do not change the EFFECT of gearing
your break question would be answered by the same

 

[05kj6spd]

Not sure what you are trying to simplify there. I fully grasp the concept of how gearing helps the engine. It changes RPMs which in turns puts it in a different part of the power curve. It also gives a mechanical advantage which is why a the old trucks and jeeps with 75 HP motors came stock with 5.13 gearing. What I was including for the original poster and what you don't seem to understand...is that along with gearing there is other things he can do to help with MPG. The width and weight of the tire will affect MPG, sorry but that is a fact. If he want's taller tires he can go taller but keep them skinny. A 235/85R16 would be tall skinny and give better MPG then a 265/70R16. Also less aggressive tread would help. An A/T vs. an M/T, never said that regearing was worthless....just that there are other things that contribute to lose of MPG.