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Old 05-03-2009, 09:22 AM   #1
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Increase power

I have a 2005 Rocky Mountain Ed. 6 cyl. 4 speed automatic daily driver with light off roading on the weekends.. I have been doing some minor mods to it whenever I get the money.
I have always disliked the sluggishness when I step on the accelerator --I figure that a lot of it has to do with the fact that it is an automatic and not a manual tranny (I could be wrong).
I was wondering if anyone had any suggestions for a relatively cheap way to boost the power. From what I have read, aftermarket air intake mods don't do much and a re a waste of money. Is there anything else that might help?
(I just had a complete tune-up and that didn't help at all).

Thanks

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Old 05-03-2009, 09:49 AM   #2
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you could always drop in a stroked 4.6l or even a 350.

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Old 05-03-2009, 10:14 AM   #3
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you could regear it for some better power.

cold air intake
header, and header pipe
hi flow cat
cat back exhaust
8mm msd wire, or equivelent
high power coil
better distributor
msd ignition box
get rid of air conditioning
take of cylinder head and get port polish, bigger valves, better roller rocker arms
bigger fuel injectors
bigger fuel pump
bigger fuel lines
electronic computer controller
flex fan


you could do all that stuff but who knows how much power you will actually get from it. Im sure plenty, but will it be worth all the money and labor that goes into it....I would say know.
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Old 05-03-2009, 12:05 PM   #4
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dweilmd,

It's weird that you say that it's sluggish on take off. I have an '06 w/ auto, and mine leaps whenever I depress the "go" pedal even moderately. But I also have a D44 w/ 3:73, and a k&n drop in replacement (don't think that has really anything to do with it though).
Have you tried running sea foam through your engine? You might have some build up that could probably use a good cleaning.

Hope some of this helps
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Old 05-03-2009, 01:07 PM   #5
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Originally Posted by KBR97 View Post
you could regear it for some better power.

cold air intake
header, and header pipe
hi flow cat
cat back exhaust
8mm msd wire, or equivelent
high power coil
better distributor
msd ignition box
get rid of air conditioning
take of cylinder head and get port polish, bigger valves, better roller rocker arms
bigger fuel injectors
bigger fuel pump
bigger fuel lines
electronic computer controller
flex fan


you could do all that stuff but who knows how much power you will actually get from it. Im sure plenty, but will it be worth all the money and labor that goes into it....I would say know.
I hate to be so blunt but most of those are complete wastes of $$$ and won't add low-end power and most like the fuel related items won't add any power at all. The best advice given was to regear the axles to a lower ratio which is a sure bet.
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Old 05-03-2009, 02:27 PM   #6
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the 4.0 is a torque based motor, you cant really get much more hp out of it without doing major internal mods like a stroker kit. chips are fairly worthless because they only work at wot. as you said the stock intake is designed very well so aftermarket parts are purely for looks. the 4.0 comes with a header from the factory and aftermarket parts dont help that much there. a better flowing exhaust will give you a little but not that much. if you want more off the line power then you want lower gears but they will increase your rpms at highway speeds. my urge for more power will be satisfied when i put a v8 in it, until then im fine with the 4.0
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Old 05-03-2009, 02:38 PM   #7
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Originally Posted by Jerry Bransford View Post
I hate to be so blunt but most of those are complete wastes of $$$ and won't add low-end power and most like the fuel related items won't add any power at all. The best advice given was to regear the axles to a lower ratio which is a sure bet.
yeah i was just spitting out a bunch of stuff off the top off my head. But I would still think all those mods put together would add up to some power. But like I said would be a waste of money compared to the amount of power you'll actually gain.

Regearing is definately the way to go.
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Old 05-03-2009, 03:32 PM   #8
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Just realize that few exteral mods will do a thing on the TJ... bigger fuel injectors/fuel lines won't do a thing because the computer will just shorten the pulse duration to keep the air fuel mixture ratio at what it wants. 8mm ignition wires won't because the low amperage of the spark voltage means it is unaffected by the normal (and required) resistance (which is added on purpose for electrical noise reduction reasons) in OE ignition wires. A better distributor won't because his TJ doesn't have a distributor. An electronic computer controller? The TJ already has one. A bigger fuel pump won't help because the existing fuel pump already pumps out more fuel than the injectors can handle which is why there is a fuel return line that returns the excess fuel back to the tank. A header won't help, the TJ comes right from the factory with a header. While older vehicles can benefit from an aftermarket ignition system like MSD makes, the TJ will not as the current computer controlled ignition system is totally integrated into the computer and an external system would still be under control of the main computer. Even a hotter spark won't help since the existing spark is already hotter than required to easily ignite the air fuel mixture. Most modern engines have gone to very good ignition systems in order to pass the stringent smog tests most states have. The days of crappy ignitions that could easily be improved like my old '57 Chevy 283 engine had are over.

Many of those listed might help earlier non-computerized engines but few of those would do much for a TJ's totally computerized engine.

All this is why when people ask about more power, the only real ways to accomplish that is by regearing, turbocharging or supercharging, or doint internal engine mods. There's nothing cheap or easy that will make a real difference in performance or fuel economy where the TJ's computerized engine is concerned.
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Old 05-03-2009, 06:22 PM   #9
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I appreciate all of the advice. I guess there isn't a cheap/easy solution. I'm not really up to doing any major engine mod's or regearing (maybe someday). I'll start cheap with the sea foam and see what happens. For now i guess i'll just save my money. Thanks.
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Old 05-03-2009, 08:20 PM   #10
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Just realize that few exteral mods will do a thing on the TJ... bigger fuel injectors/fuel lines won't do a thing because the computer will just shorten the pulse duration to keep the air fuel mixture ratio at what it wants. 8mm ignition wires won't because the low amperage of the spark voltage means it is unaffected by the normal (and required) resistance (which is added on purpose for electrical noise reduction reasons) in OE ignition wires. A better distributor won't because his TJ doesn't have a distributor. An electronic computer controller? The TJ already has one. A bigger fuel pump won't help because the existing fuel pump already pumps out more fuel than the injectors can handle which is why there is a fuel return line that returns the excess fuel back to the tank. A header won't help, the TJ comes right from the factory with a header. While older vehicles can benefit from an aftermarket ignition system like MSD makes, the TJ will not as the current computer controlled ignition system is totally integrated into the computer and an external system would still be under control of the main computer. Even a hotter spark won't help since the existing spark is already hotter than required to easily ignite the air fuel mixture. Most modern engines have gone to very good ignition systems in order to pass the stringent smog tests most states have. The days of crappy ignitions that could easily be improved like my old '57 Chevy 283 engine had are over.

Many of those listed might help earlier non-computerized engines but few of those would do much for a TJ's totally computerized engine.

All this is why when people ask about more power, the only real ways to accomplish that is by regearing, turbocharging or supercharging, or doint internal engine mods. There's nothing cheap or easy that will make a real difference in performance or fuel economy where the TJ's computerized engine is concerned.
ok so listen up dweilmd...forget everything I said. Just regear the damn thing. LOL.

You know Jerry as soon as he said "i want more power" I went right into Hot Rod mode, lol. Thinking back to my 87 monte carlo SS with a balanced 355ci.
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Old 05-03-2009, 11:27 PM   #11
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There was a good TRUCKS episode on Spike TV today that had them dyno a cherokee with the inline 6. They claimed it only made 35 hp. I didnt get to finish the show but they bored it over, added new cams, and what not. Did anyone else watch this and the results?
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Old 05-04-2009, 01:28 AM   #12
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There was a good TRUCKS episode on Spike TV today that had them dyno a cherokee with the inline 6. They claimed it only made 35 hp. I didnt get to finish the show but they bored it over, added new cams, and what not. Did anyone else watch this and the results?
Next weekend they should show the results.

Man that was quite a costly rebuild...wonder why they didn't just go with a V8?
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Old 05-04-2009, 09:39 AM   #13
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I think it was also supposed to be a stoker motor too.
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Old 05-04-2009, 12:04 PM   #14
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yeah....I believe they said a 4.2. Dunno, definately said it was .40 over and they increased the chambers to like 60cc from 57(?), I'll have to look again, that epi got DVR'd
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Old 05-04-2009, 12:09 PM   #15
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Jerry,
Would a cam help out the 4.0 at all?
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Old 05-04-2009, 12:22 PM   #16
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I personally wouldn't install a performance cam unless I was planning to race my Jeep at the drag strip or I was racing up steep sand dunes on a regular basis.
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Old 05-04-2009, 01:48 PM   #17
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I have seen ones that supposedly give more low end torque. I figured it wouldn't help much just curious.
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Old 05-05-2009, 06:41 PM   #18
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Did the sea foam thing, both in the gas tank and in the vacuum line from the brake booster -- I'm pretty impressed. Major difference in acceleration and power. Thought that maybe it was my imagination, but even my girlfriend noticed a difference from the passenger seat. ?? could it be that easy (and cheap)?? I'm going to try 2 more cans in a couple of weeks.
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Old 04-09-2015, 04:59 AM   #19
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Just seen this thread (bit behind as usual), what is this sea foam stuff please ?
Please bear in mind that I have a UK 2001 RHD 4.0L TJ.
This forum has steered me away from the idea of air intake & throttle body mods btw.
Im thinking gears & a wider bore exhaust.
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Old 04-09-2015, 06:01 AM   #20
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I regeared to 4.88 running 33s on 17" wheels and replaced both my axles with D44s and I have good pick up off the stop light but the reality is a Jeep with a 4.0 L engine is not going to have a lot of high end performance...but at the same time you cannot break the thing either. It's an engine that takes a kicking and keeps on ticking (sorry Timex).
I also just installed a MagnaFlow Exhaust and a new MagnaFlow Catalytic Converter and the Jeep seems to like it, it seems to run a bit smoother. I cannot attest to anymore performance from the exhaust, although I am sure it picked up a little.
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Old 04-09-2015, 08:25 AM   #21
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Remove your throttle body and completely clean it and your AIC (air intake control). pick up a 2 dollar gasket in case the old one doesn't come off clean. If you don't know how to do this, just look up on you tube "how to clean throttle body Jeep 4.o"
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Old 04-26-2015, 12:12 PM   #22
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Looking for MR. GoodBar aka more pwr/trq

Lets just say for a moment that one was willing to rebuild a 4.0L H.O. Wrangler power plant short block and wanted to port match the head with both manifolds, polish the bowls, enlarge the valves and rebore a over 200K motor.

Where would you start when it comes to the cam and crank if you wanted more low end power on and off road if you already had 3:55 gears following a 5 speed pushing 33X12.5x15's and a 6 inch RC lift? If you going to build a 4.0 with the superficial mods and want the most out of the build, I may suggest in looking at the programmer like the Jet Stage 2 for the appropriate year, but 91 Octane is recommended Jet Performance 90015S - JET Performance Stage 2 Module for 97-03 Jeep® Wrangler TJ with 4.0L Engine - Quadratec and the other programmer from Hypertech 52500 lets you interface with the settings and choose the tire size and if your using 91 octane or regular octane and is a little more $ but may be worth it all things considered to be equal, Hypertech 52500 - Hypertech Max Energy Power Programmer for 97-04 Jeep® Wrangler TJ & Unlimited, 96-04 Grand Cherokee ZJ, WJ and 96-01 Cherokee XJ - Quadratec Im looking at something soon myself. I drive about 45 miles Round trip each day and occasionally go off road so I want more torque on the road mostly in 4th and 5th gears but don't want to move down in tire size. I was considering a Cam but the tuners didn't indicate that would help. I also thought about stroking the cam to a 4.2 but have had no confirmation that would yield any HP increase for the $$ it would cost to go that direction. I am open to rational suggestions that don't include nitrous, supercharging or forced induction. I have had motors with those and they always end up costing more $$ in the long term and the motor never holds up as long as the stock builds do. I am open to suggestions from the Forum
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Old 04-26-2015, 12:25 PM   #23
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Lets just say for a moment that one was willing to rebuild a 4.0L H.O. Wrangler power plant short block and wanted to port match the head with both manifolds, polish the bowls, enlarge the valves and rebore a over 200K motor. Where would you start when it comes to the cam and crank if you wanted more low end power on and off road if you already had 3:55 gears following a 5 speed pushing 33X12.5x15's and a 6 inch RC lift? If you going to build a 4.0 with the superficial mods and want the most out of the build, I may suggest in looking at the programmer like the Jet Stage 2 for the appropriate year, but 91 Octane is recommended Jet Performance 90015S - JET Performance Stage 2 Module for 97-03 Jeep® Wrangler TJ with 4.0L Engine - Quadratec and the other programmer from Hypertech 52500 lets you interface with the settings and choose the tire size and if your using 91 octane or regular octane and is a little more $ but may be worth it all things considered to be equal, Hypertech 52500 - Hypertech Max Energy Power Programmer for 97-04 Jeep® Wrangler TJ & Unlimited, 96-04 Grand Cherokee ZJ, WJ and 96-01 Cherokee XJ - Quadratec Im looking at something soon myself. I drive about 45 miles Round trip each day and occasionally go off road so I want more torque on the road mostly in 4th and 5th gears but don't want to move down in tire size. I was considering a Cam but the tuners didn't indicate that would help. I also thought about stroking the cam to a 4.2 but have had no confirmation that would yield any HP increase for the $$ it would cost to go that direction. I am open to rational suggestions that don't include nitrous, supercharging or forced induction. I have had motors with those and they always end up costing more $$ in the long term and the motor never holds up as long as the stock builds do. I am open to suggestions from the Fourm
3.55's arent the right ratio. You need 4.56's. That will get you more torque
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Old 04-26-2015, 12:44 PM   #24
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Not the right ratio

I realize that now, however I haven't gotten around to change them after putting the ties on. I swapped the front Axle out from a 91 Cherokee after I found my front axle cracked. I then realized that the ratio from the Cherokee was different from the Wrangler, I went back to pick up the matching rear axle. I had to FAB alot to get that rear axle to fit. I didnt want to swap out the centers and fool with the preload of the ring/pinion. Lazy mostly. Until I saw how much fab work was needed, in for penny in for pound I guess. These different 3:55 ratio's were taller than the 3:08's that were on there but I had smaller tires on then also. So Yes I know I can take this to a taller ration but I will have to do both so I wanted to just build what I had for now so it will be even better when I swap ratio's again. I have been happy with the RPM range on the HWY but would like the 200K 4.0 to be stronger to use the same installed ratio for now. I'll keep that ratio in mind when I go looking for Lockers for the Axles, Thanks.
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Old 04-26-2015, 04:24 PM   #25
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Just curious if the 4.0 can handle a moderate 2 stage boost (10-12 psi) or do you have to dig into the engine and upgrade to forged internals?
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Old 06-04-2015, 11:55 AM   #26
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Are you wanting to apply a forced induction mod onto the 4.0? If so you may need to consider the Pistons, rings and bearings as well as the Cat muffler and piping to ensure that that extra flow has an efficient exit, otherwise the crank case could apply additional pressure on the rubber seals and gaskets causing additional issues. Unless I build from the bottom up for that forced induction purpose, I would not put an already broken in engine to that torture test.$$$$$

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