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-   -   4.0L I-6 engines... Any performance mods available (

KDOG2008 06-13-2010 03:20 PM

4.0L I-6 engines... Any performance mods available
I guess I should specify by saying that I'm not interested in losing too much MPGs'. Maybe what I should say I'm interested in "enhancements". I'm not talking about a complete teardown, just things that could be done to boost power/torque that are relatively simple for a noob like me.
Any suggestions?

papi32 06-13-2010 08:20 PM

exhaust helps a little, i put a dynomax ultraflo muffler on my 99 wrangler 4L with stock pipes and it seems to get up to higher rpms a little faster but its nothing really to brag about, and the sound is not much louder than stock but still has a nice deep rumbel to it, sounds awsome when you put it to the floor!!!

hustler905 06-13-2010 08:25 PM

In my personal experience things that do not work and increase annoyance down the road are:
- throttle body spacers
- "performance" exhausts
- conical filter systems

Things that do make a difference at the expense of fuel economy:
- power programmers

Things that might make a tiny difference:
- synthetic fluids

That is all, based on what I have used in my own Jeep.

ClimbStuff 06-13-2010 09:32 PM

The 4.0L sort of defies the laws of engines... it doesn't really respond noticeably to much of anything unless its internal... and then the internal mods wake up with the supporting breathing mods... very weird engine IMO.

RogueSpear2023 06-13-2010 11:33 PM

I think some the reasons that the I6 has problems with simple mods is first design it has been around for a long time, it's and I6 like and old tractor engine, not much you can really do to increase performance. It has 2 valves per cylinder where many new vehicles have 3 or 4. Also the I6 was at the end of the road when Chrysler replaced it, I think Chrysler did everything they could to squeak out every last HP, and TQ out of old engine design, it was tuned by Chrysler, not detuned like many cars and trucks that come out these days. About the only mods that will increase power are some type of forced induction, a stroker kit, or a V8.

KDOG2008 06-14-2010 07:37 PM


ajmorell 06-14-2010 08:03 PM

I didn't realize any real improvements until I compounded mods. I'm running a 99+ intake manifold, aftermarket cam, header & full exhaust (high-flow cat, flowmaster) and there is a substantial difference compared to the stock 4.0.

chainz 06-15-2010 05:02 PM

I agree with hustler 100% the only solution i feel once you get the itch to go faster or make your engine stronger is a V-8 you will just be wasting money on bolt on parts that in my experience don't really do a whole lot.

Jeepxj5209 06-15-2010 05:04 PM

replace your manual fan with an electric one
-free up a few ponies
-No annoing winding sound
-more efficent in traffic
/ offroad

GeologistFelix 06-15-2010 05:51 PM

Then there's the classic stroker mod. It violates the 'not wanting to tear the whole engine down' stipulation, but it's still worth mentioning.

Basically, you use parts from an older 258 6-cylinder with the 4.0L block, and increase your displacement, usually to around 4.5L (you can go up to more like 4.7L with some more serious aftermarket parts and some machining).

The cheapest stroker built will give you a solid 30ish HP and a good 50 ft/lbs more torque, and it doesn't use appreciably more gas than a stock engine for regular driving...however, it *can* burn a lot more gas than a stocker when you want it to. Like, when you're on short freeway onramps, or mudding.

Bryson 06-15-2010 07:04 PM

It's all about boost...

How To: Build your own 4.0L turbo Cummins (Beware...170+ pics) - NAXJA Forums -::- North American XJ Association

Wheelin98TJ 06-15-2010 10:06 PM

Bolt on mods are a waste on a stock 4.0 I6.

Consider selling the I6 WJ and pick up one with a 4.7 V8.

Unless you're attached to your Jeep, I think this is the easiest and best way to pick up some horsepower.

RubiconBlack 06-22-2010 02:48 PM

I have a Airraid Cold Air intake and a Banks Cat Monster Exhaust on my 04 Rubicon. I didn't notice any difference until I added a Poweraid Throttle Body Spacer. I went from gettting 200 miles per tank to about 240 to 250 miles per tank. I worked for me but I have heard it hasn't work on others.

-ExDementia- 06-22-2010 03:25 PM

Individual mods do nothing pretty much, but when you get exhaust + intake + other misc stuff, it will net you a noticeable amount. But if you do them all one at a time, you really won't notice anything. You might think you do though!:D

ajmorell 06-22-2010 06:57 PM


Originally Posted by ExRecon (Post 9670260)
Individual mods do nothing pretty much, but when you get exhaust + intake + other misc stuff, it will net you a noticeable amount. But if you do them all one at a time, you really won't notice anything. You might think you do though!:D

That statement makes no sense at all. Are you saying if you don't do them all at the same time you will notice something?

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