You can either buy or design a cold air intake for your jeep with some noticible horsepower difference. This works on the principle that the density of cold air is greater that the density of warm air. Therefore it holds more oxygen molecules per cubic inch. The more oxygen in the reaction, the greater the force of the explosion inside your engine, the result being an increase in overall horsepower.
Now the true cold air intake is completely isolated from the engine compartment. It seperates the gasses and high temperatures that are a byproducts of your engine. I elected to go with a "semi" cold air intake. I bought an APC pipe and filter from Pep Boys for a Honda Civic. Yeah, yeah -RICE, I know but it was cheap!
I cut it off and connected it to the stock rubber hose that goes into the Throttle body. I routed it straight forward (as opposed to the ones that go across your engine resulting in higher temperatures) to where the stock airbox would be getting its input from the radiator. This area of the engine compartment produces colder temperatures because it is being fed from the outside constantly.
After doing some research, I found that the difference between the 2.5l Throttle body and the 4.0l is the inside diameter of the intake. The rest of the throttle body is cast and it has the same bolt pattern and sensors -with the exception of the 1990 or earlier models which are non-multiport fuel injected. These throttle bodies have 3 bolts as opposed to the 4 bolts in the MPFI models. Again this works on the more air principle. The 4.0l Throttle body will increase the amount of air going into your combustion chamber resulting in an increase in horsepower.
I decided to use a poweraid spacer in conjunction with the 4.0l Throttle body. According to poweraid:
The Poweraid TBS concept was developed to enhance mid-range power, torque and fuel efficiency. The unique dyno-proven "Helix Bore" causes a spinning action of the incoming air charge as it passes through the throttle body. This extremely beneficial air-charge carries all the way into the combustion chamber, producing a super-atomized mixture and resulting in tremendous gains in mid-range power and overall efficiency.
Now I'm not sure about the helix bore concept but I do know that a spacer between the throttle body and the intake manifold will "fool" the computer into thinking it needs more air in the air fuel mix. This is where your horsepower gains come from.
MAKE SURE YOU DONT LET ANYTHING FALL INTO THE MANIFOLD , this goes directly into your engine.
When you first start your Jeep up, You will notice that it will idle real high and will take a few minutes to return to normal. Remember everything is computer controlled so the computer has to adjust itself to the new airflow. This should only take a few min. On your test drive you should be able to feel the difference in horsepower mostly in 2nd and 3d gear, you will be able to hear the whistle created by the "helix bore". This is also normal. The computer works on averages so it will take a few miles for the computer to completely adjust.
Thats it! your done, enjoy your Horsepower and added torque on the road and you might even get your 5th gear back!
If you really want to maximize the flow of air through your vehicle and see an improvement in horsepower, there is one more thing you must consider.
In addition to the cold air intake and 4.0l throttle body, you need to increase volume of air that is exiting the engine. All of that increased air flow has to go somewhere, and your stock exhaust system is set up for maximum fuel economy instead of power so the diameter of the pipes and the amount of airflow through your catalytic converter is relatively low. this theory applies to everything from plumbing to network engineering: Your flow is limited to the smallest entity in the chain
A true system will have you replacing your pipes from the exahust manifold back. You can take your pick of performance exhausts including remus, dynomax, borla, and many others on the market today.
Some people hollow out their catalytic converter or eliminate it completely. This is not reccomended, it will decrease the backpressure in your engine and will make your Jeep illegal depending on what state your from. I suggest taking your time and replacing exhaust components one at a time, starting with the muffler and tailpipe. A good exhaust will set you back, but is worth it in the long run.
You can replace the chip for a couple of hundred dollars. One of the lead computer manufacturers is a company called "Jet" and can be bought through places like quadratec. It can be difficult to find chips for 4 cyl Jeeps though.
If there is more air, then there is excess oxygen. This is called a lean mixture. A lean mixture can cause poor performance and even engine damage. Like I said before, it will run hot in race cars and wind up melting stuff. A rich mixture results If there is less air then there will be fuel left over after combustion. This is where you see black deposits in the exhaust or on the pipes. This is where the 02 sensor comes in. The main purpose of the oxygen sensor is to help the engine to run as efficient as possible.
The oxygen sensor is located in the exhaust pipe right in front of the cat, and can detect rich and lean mixtures. The Oxygen sensor uses a chemical reaction that has voltage as a byproduct. The sensor has a tube made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions. Sounds kinda like binary huh? The engine's computer looks at the voltage and determines if the mixture is rich or lean, and adjusts the amount of fuel entering the engine through the fuel injection system.
When the oxygen sensor is worn or broken, the computer does not know what your fuel/air ratio is, so it ends up guessing. Your car runs like crap and uses more fuel than it needs to. I was off roading and actually ripped mine completely out on a tree. The Jeep would idle real high, then real low , real high, real low. I though something was really messed up. I looked under and saw it hanging.
If your Jeep is old you may want to swap this out anyway, it will give you better gas mileage. You can get one at the parts store for around $40.
