Exhaust

Todays topic I would like to discuss are headers. Over the years there have been many different styles of headers produced for the 4.0L motors that are pre-02 when the mid-model revamp took place. Chrylser decided to add pre-cats to the motor thus making it difficult to produce a header for the 4.0L. Years ago I had to make the decision because like many others that have the 4.0L probably had their exhaust manifold crack within 5 or 7 years. My Jeep was ran for years with a cracked manifold and I decided it was time to upgrade my exhaust so I did my research and decided to go with the Mike Leach Headers (see Previous Work for image) with 2.5" exhaust including a Magnaflow high-flow cat and Flowmaster 50 SUV series. There are many companies out there who make a great header such as banks, doug thorley, edelbrock, and gibson. It also just so happened that Mopar Performance produced a header developed by Mike Leach, and it just so happened, that is the header I purchased. These headers are true performance using a long tube design in a tri-y form that end up running all the way to the bottom of the motor.

Only problem with these headers for those who want the most out of their 4.0 is that these headers have not been produced for years and are not very common. There is hope, if Mike Leach can get 20 people to be interested and put money down, there is a chance he will produce another batch, if you would be interested, contact Kolak on Jeepsunlimited and express your intrest.

Another addition I made while doing the exhaust and having the motor torn down was to do a common mod involving updating the intake manifold. Mine was done using an intake manifold from a 2002 Jeep Grand Cherokee with the 4.0L. The air ducts are designed with less bends and an increase in the volume that the manifold is able to hold. The volume in the new manifold is 4.3L which is an increase from the 2.6L held by the older style of manifold. I have attatched a picture of the differences between the years, the one on the right is the new updated version. I have also attatched what it looks like installed.

If you are wondering, this is a direct bolt on, you can also use the newer updated fuel injectors however you will need to make it work by either soldering in new connectors or filing down the hold down and use wireties or use your creativity to keep them held down, I opted to reuse my injectors. Here is a great write-up that holds alot of information regarding this mod.
Intake Manifold Swap

My personal opinion regarding the exhaust on my Jeep is certainly a great one. The sound that the Flowmaster 50 SUV Series produces has a mean rumble and doesn't sound bad or have an annoying drone. The mod was done years ago and I have since then forgot what it felt like before but the feel of the power increase was certainly worth the money. My gas mileage went up 1-2mpg as well which is a pleasant surprise.