Valve Cover Replacement

  After living with the valve cover conversion for a couple of months now it seems that I have licked my blow by problem. There may be a number of reasons for this. One is that the later model valve cover, as I stated before, twist in and create a more air tight connection. Another may be that the PCV unit is separate from the hose and larger, therefore may be more capable of handling crank case vacuum. Lastly, although the picture below does not show this but I removed the small white filter you see in the front of the cover and ran the line back into the air filter converter tube. After additional research I learned that since this was a closed system that my separate crank filter may have been increasing my blow by problem. I like the clean look and function of the new setup and would recommend it as a low dollar possible fix. I can't guarantee that it will in every instance, since there are a number of problems that can cause blow by, but it seems to have worked on mine.

Producing Power

There are two primary areas that account for the largest percentage of bolt on performance products. They happen to also be the top two areas of possible performance gain available. Oddly enough, often, its two of the most misunderstood areas under the hood of most vehicles. Any internal combustion engine must ingest air and fuel and that mixture must be ignited. Those burnt gasses must then be expelled so that new gasses can take their place. If an engine does not taken in, ignite and expel those gasses efficiently it will not produce quality power. In producing power with the 4.0, I have already done the easy items. In my article on the K&N conversion we increased the capability for the engine to take air in. I have also put in a high flow FlowMaster muffler and Dynomax cat. Therefore, the engine is able to better utilize the increased intake by increased exhaust system capability. So, I am now bringing in more air and expelling more air (the engine, not me) but what have I done to make sure that I am properly igniting that mixture. We need to address the engines capability to ignite and burn those gasses. Since we are not going to be getting into the combustion chamber to modify its capacity or efficiency, the only way to effect change in this area is with the spark efficiency.

Spark Plugs

This, in my opinion, is an area of great debate. Everybody has an opinion and a favorite. I have used everything from your base line AC, NGK or other factory replacement plug to top of the line platinum or specialty design plugs. I am now currently using Splitfire spark plugs. I have not run them on a dyno, so I can only give you my gut feel on them. I did see a moderate increase in gas mileage and a slight seat of the pants power change. I don't know that most of you will notice a perceivable difference in power as I have. I imagine that after, roughly, 23 years of messing around with engines I may notice subtle changes more than others. I also know exactly how my Cherokee performs, therefore I did notice this slight difference. My suggestion to you is that you use a top of the line platinum plug or something similar to the Splitfire plug. I believe that they both have better designs and will accomplish the first step in what we desire, and that's a hotter fuller spark.

Plug Wires

The second step in our increased spark/burn combo are the plug wires. Again, there are a lot of product prejudices when it comes to plug wires. I personally like Accel 8.8 series wires. I do not like custom wire sets. I suggest buying a set of quality performance plug wires that are premade for your specific engine or engine type (4,6,8 cylinder). Custom wires that require cutting and fitting of plug ends often cause problems. If the job is not done properly you will loose spark efficiency. Ceramic vs. Graphite vs. Copper vs. braided is also a personal preference. I am fairly sure that if we did a comprehensive test of all of the available performance plug wires that we would probably find less than a volt difference between brands. Like with spark plugs, just make sure that you buy a quality set of wires made for your engine or engine type.

Spark Discharge

A final area of possible performance enhancement is in spark discharge. I have long used MSD products in my vehicles. They have recently come out with a new product made just for us off roaders. The MSD 6 Off Road provides a number of very valuable features in ignition control. First of all it provides powerful multiple discharge. This is to say that it produces multiple sparks per burn rather than just one. The number of sparks per burn varies with rpm but will provide with a more even burn throughout the combustion chamber, thus producing more power and efficiency. Another great feature to the Off Road unit is that it is waterproofed. All connections as well as the case are have been treated to a number of waterproofing treatments. The connectors are weathertight connectors for positive waterproof seals as well. The unit also comes with shock dampening mounts which when added to the waterproofing are the perfect combo for the off roader. Installation is fairly simple and made simpler with the addition of their wiring kits for each vehicle. For the 4.0 in the Cherokee this kit number is PN #8813. The MSD 6 Off Road part number is PN #6470. The instructions for the main unit are detailed and cover a number of applications. The instructions for the wiring kit are very straight forward and provide more information on install into the Jeep Coil Pack. I highly recommend getting this wiring kit as it has a number of spacers needed to properly and easily install the MSD unit. Essentially locate the Coil Pack on the passenger side fender well. Disconnect the wires and remove this unit via the instructions. Once out of the vehicle you will need to take the Coil Pack apart separating the coil and ignition module and modify it slightly. This is very easy and only requires drilling a 11/64 hole to mount a screw in as seen below.