Making a 4 cylinder Jeep work for you is a possibility. These little motors are reliable and decent on fuel. They run forever and require little maintenance. The only complaint most owners have is a lack of power. Rowing the transmission through the gears is often the only way to keep up with freeway traffic on any kind of hills. So what choices do you have for more power?

Engine Swaps:
First off, unless you are a total masochist you will want to avoid trying to install a 4.0L six cylinder. Jeep made a huge number of modifications in 1987 to install the six and it would be necessary to transfer all those components in order to stuff the long inline motor under the hood. To install the 4.0L into an older Jeep you would have to make a complete front core support change, moving the radiator forward more than a foot, change the hood and catch to match, and firewall modifications would be needed to allow the extended motor to fit back nearly under the dash. You would also have to change to a newer fuel pickup with an electric fuel pump and all new fuel lines as well as adapting the newer fuel injection engine harness into the older Jeep's wiring harness. Finally there are many small things that were changed. All of these items combined make this swap an economically unlikely job. Basically if you want a 4.0L motor sell your Jeep and buy one that came with it stock.

Other motors could be used, but the engine compartment is surprisingly small and makes any installation difficult. Many people assume a Chevy 4.3L V-6 would be an easy swap, yet when measurements are taken this motor is similar in size to the 4.0. The exception is width as the V-6 is considerably wider and creates exhaust clearance problems. In fact, Advanced Adapters clearly states in their catalogue to avoid this swap if it is to replace either a 2.5L 4 cylinder or a 2.8L 6 cylinder engine. "This swap is best done only to Cherokees originally equipped with a 4.0L six." (writers note: In my opinion this would be a step backwards!).

Another engine that could be used is the 2.9 liter V-6 used in Ford Ranger pickups and some passenger cars. The ideal motor appears to be the unit used in the Merkur Scorpio as it has the lowest intake manifolding and produces the most power. This motor is very compact with measurements very similar to the stock Jeep 2.5L. Width is narrow as this is a 90 degree V instead of 60 degrees like the Chevy engine. I have investigated doing this swap to my own Jeep and determined the best setup would include a Ranger or Bronco II automatic transmission with the Ford transfer case behind that. All of these parts should bolt together with no need for aftermarket adapters reducing the cost of a swap considerably. However, attempting it would require a number of custom parts as all motor and transmission mounts would have to be custom fabricated and the fuel injection would have to be made to operate. This would need to be done by an expert as no simple stand alone harnesses are available. Simply put; doable but not easy.

Adding More Power To A 2.5L:
This is the route I have taken with my Jeep. I determined that the cost and effort involved with swapping a motor simply isn't worth it to me. Others may have the money and feel the need to install a different motor into their Jeep, but they are few. Most of us would be happy with a bit more power without having to do anything extreme. Below are some things I have done to improve my Jeeps performance. Some of these items may not be legal modifications in some states due to emission laws.

The first modification I performed was the addition of a Weber carburetor. The model is the 32/36 downdraft. This carb is designed to replace the original single barrel unit without having to change the intake manifold. Overall it is a big improvement from a performance standpoint. A gain of 10-20% in horsepower was noticeable from the moment I took it for a test drive. My only gripe about the Weber is cold driveability suffered as the choke operation is not as smooth as I would like. However, I believe this problem may be only with my carb. as a friends Jeep with the same setup works much better than mine. At about $300.00 this upgrade is well worth the money especially if the original equipment carburetor is worn out.

My next upgrade involved "recurving" the advance curve in my distributor. I performed this myself, but most people should have a local "speed shop" do the operation. What you want is to find an outfit that has a distributor machine. This will allow them to tailor the advance curve to meet your engines' need. Recurving the distributor helps get the most out of your engine with the new carb installed. Once completed you will find your engine pulls better throughout the RPM range and is much stronger near the top. At this point it is a good idea to add some good performance plug wires as well as new spark plugs and other tune up parts. This assures maximum efficiency.

Exhaust upgrades came next with the addition of a free flowing muffler and tailpipe assembly. Most good muffler shops can custom build an exhaust system from the catalytic converter back with larger pipes and a large chamber muffler. With the other modifications the exhaust improvement should net another 5% increase and make your Jeep sound faster too.

From this point on the gains become less. I have added a FlexFan performance cooling fan to reduce parasitic power loss and improve cooling. Very small gain here. Other than that at this point the rest of the motor is virtually stock inside with the exception of .30 overbore pistons at the last rebuild. My future plans call for a complete rebuild of another 2.5L with high performance as the main goal. I will also try to add some form of fuel injection to improve off highway driveability at extreme angles. Watch for the build in a few issues.