Underpower jeep- need advice
03-20-2011, 10:10 PM
#11
JK Freak
I know your pain, my Jeep is real sluggish these days with after market front and rear bumpers and well as rock sliders. Gearing will get you far better performance than superchips does.
03-21-2011, 02:41 AM
#13
JK Jedi Master
First, you should find out for sure if it is or isn't. Easiest way is to jack up the Jeep and count driveshaft revolutions as you rotate the tire one time.
Second, with an auto and 33s, 4.88 gears will make a very nice boost in seat-of-the-pants performance.
Third, while I don't disagree with the poster who commented that top end power will never be great with this engine, you will see a very definite boost in top end performance from a regear. This is for two reasons:
1) The simple mechanical advantage of the regear. Going from 4.10s to 4.88s gives a 19% bump in torque. That will be experienced at all RPMs.
2) Because of the regear, at any given speed on the highway you will be running at higher RPMs than before the regear. If you take a gander at the 3.8L torque/HP curve (kandn.com/dynocharts/57-1553_dyno.pdf), you will note that at higher rev's you will have more torque and HP to tap. For a six speed (because I have those charts/calcluations at hand), the difference between 4.10s and 4.88s at 70 MPH is 80% improvement in HP and a 55% improvement in torque. And, that's even greater than you may realize because you've already paid the penalty for friction in the drivetrain--almost all of this HP/torque increase will make it to the wheels.
I had my Jeep (six speed) regeared from 4.10s and 33s to 4.88s and 35s. The butt-factor with this change made driving my Jeep a lot more fun. I just returned from a drive out to San Diego and its performance was dramatically better. Could I use more? Sure. But, I didn't have to resort to third gear on the Interstate, and if I left it on cruise in sixth gear while going up a typical hill, I usually lost no more than about 5-6 MPH (there were a couple very windy days that were a bit worse). Before, I'd have been down-shifting at least once, and maybe even twice. And remember: This not only included a regear, but moving from 33s to 35s.
Do it, you won't regret it. Here in the lower (upper?) 48 the cost is about $1K--add a couple hundred for a full rebuild kit with new bearings. It was worth every penny.
Second, with an auto and 33s, 4.88 gears will make a very nice boost in seat-of-the-pants performance.
Third, while I don't disagree with the poster who commented that top end power will never be great with this engine, you will see a very definite boost in top end performance from a regear. This is for two reasons:
1) The simple mechanical advantage of the regear. Going from 4.10s to 4.88s gives a 19% bump in torque. That will be experienced at all RPMs.
2) Because of the regear, at any given speed on the highway you will be running at higher RPMs than before the regear. If you take a gander at the 3.8L torque/HP curve (kandn.com/dynocharts/57-1553_dyno.pdf), you will note that at higher rev's you will have more torque and HP to tap. For a six speed (because I have those charts/calcluations at hand), the difference between 4.10s and 4.88s at 70 MPH is 80% improvement in HP and a 55% improvement in torque. And, that's even greater than you may realize because you've already paid the penalty for friction in the drivetrain--almost all of this HP/torque increase will make it to the wheels.
I had my Jeep (six speed) regeared from 4.10s and 33s to 4.88s and 35s. The butt-factor with this change made driving my Jeep a lot more fun. I just returned from a drive out to San Diego and its performance was dramatically better. Could I use more? Sure. But, I didn't have to resort to third gear on the Interstate, and if I left it on cruise in sixth gear while going up a typical hill, I usually lost no more than about 5-6 MPH (there were a couple very windy days that were a bit worse). Before, I'd have been down-shifting at least once, and maybe even twice. And remember: This not only included a regear, but moving from 33s to 35s.
Do it, you won't regret it. Here in the lower (upper?) 48 the cost is about $1K--add a couple hundred for a full rebuild kit with new bearings. It was worth every penny.
Last edited by Mark Doiron; 03-21-2011 at 02:44 AM.
03-21-2011, 11:12 AM
#14
Sponsoring Manufacturer
Not to rain on your parade here but a programmer adds 10HP tops and the supercharger adds about 70HP if that. As for the headers I dont think they add 50HP cause then no one would pay $5K to gain 70HP with a supercharger.
As for the OP these engines suck so the best mod is the strip weight mod. Once my spare and rear seat came out it was like I had a new engine in my Jeep. You know you feel it already when the doors are off.
As for the OP these engines suck so the best mod is the strip weight mod. Once my spare and rear seat came out it was like I had a new engine in my Jeep. You know you feel it already when the doors are off.
whao - HOLD the train
We add 120 rear wheel HP and 90ft/lbs of torque - OTHER manufactures add much less than us...
RIPPTECH
03-22-2011, 02:11 PM
#15
JK Newbie
Join Date: Mar 2010
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Re-Gear!, I'm doing mine as soon as i get my tax return and i don't have half that weight your carrying. I currently run a superchip but sometimes i get some pinging and to be quite honest messing with the timing just isn't enough for me and after research and talking to people who know their sh*t i'm taking the plunge and going for 5.13's...
03-22-2011, 03:08 PM
#16
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re-gear
I run a heavy JKU, see profile, I regeared from 4:10's to 4:88's and got the power and MPG back and it became fun to drive again. I am now saving for a hemi swap planned for next winter.