1999 Jeep Cherokee Exhaust Install - Project XJ TrailRunner

At first glance, this looks like a head pipe with damage. Just below the exhaust manifold flange, the factory bend is tight and crushes the pipe. This is stock equipment for a '99 XJ Cherokee!

A common problem with stock 4.0L tubular exhaust manifolds is this crack that occurs above the pipe connection. The symptom is an exhaust leak that will often go away as the engine warms. Not to be mistaken for a flange leak, this is an actual defect that requires a new manifold or a proper weld (TIG) repair.

Tight bends of the connecting pipe between the stock exhaust manifold and catalytic converter are restrictive and cause backpressure. Shorter-wheelbase models have a cramped frame/chassis, and the transfer case is a wide obstacle.

Here, a new stock header pipe (background) shows the tight bends and odd pipe diameters. From the manifold flange to the first sweep, the pipe is smaller than the diameter that runs to the cat inlet. The Borla header and head pipe (foreground) offers tuned header tube runners that feed into a connector pipe with gradual bends and a large diameter over the entire length of the pipe.

No, this is not physical damage. This is a new, factory-fresh replacement connector pipe, just like the stock one on the XJ Cherokee. The inlet mouth shrinks in the area of the crush bend, reducing an already smaller pipe diameter to two-thirds its tube size! Here is a loss of power right below the manifold, stifling fuel efficiency as well.

Borla's header and cat-back system are fifty-state legal. Here, the California emission exemption number tells us that Borla has met or exceeded the requirements for emission control on this vehicle application. Improved flow and reduced backpressure will help the engine breathe better and run cleaner.

Here, I began the process of removing the original exhaust manifold. On the '99 XJ, one method is to remove the intake and exhaust manifolds together, installing the new manifold from the top side. The power steering pump must be loosened from the water pump and moved out of the way. Be assured that changing a 4.0L intake or exhaust manifold is a challenging job, even with the right tools and a chassis hoist.

I elected to remove and install the new Borla manifold/header from the bottom side. Supporting the engine with a block of wood beneath the crankshaft pulley, I removed the driver-side motor mount and cast engine bracket as shown. Raising the engine carefully (but not too much!), the space allows the manifold/header to swing in and out of position.

The new Borla header now swings into place. Borla provides a heavy-duty intake/exhaust manifold gasket. I cleaned the gasket surfaces and vacuumed away the debris from the intake and exhaust ports of the cylinder head. I then cleaned all stud and bolt threads and used antiseize compound on clean threads. This enables easier installation and future removal of the manifolds.

The Borla connector pipe to the catalytic converter is a smooth-flowing, easy-sweeping pipe. The header exit drops farther forward than the stock manifold flange, which provides the extra space for this larger-diameter, better-flowing pipe. In addition to the Borla header's precision tuning, the connector pipe assures unrestricted flow to the cat.

Borla couplings are top quality. The pipe fits the OEM position with smoother flows and durable attachment hardware. This is a long-life exhaust system that will easily meet or exceed original equipment standards. Borla is a supplier to Mopar Performance, where factory engineers make certain that products meet high standards.

Random Technology's "super high flow" catalytic converter assures the best flow without unnecessary restriction. To enhance the Borla header and connector pipe flow, I chose the Random Technology cat. The Borla muffler and tailpipe make up a cat-back system. Both factory oxygen sensors attach to these new components.

Borla equipment fits very well. Recall this is the '97 application system installed on a '99 XJ Cherokee. To enable use of the Borla tailpipe, I made a minor modification to the factory hanger, lowering the bracket while maintaining the factory bolt alignment in the body/frame. Borla has followed this installation closely and is working on a system for late XJs.

Borla routes the tailpipe in line with the frame. The '99 stock pipe ran inboard of the spring, parallel to the fuel tank shield. The new routing works nicely, protecting the pipe while moving it away from the gas tank. I made sure there was an air gap between the pipe and frame at all points.

Using the '97 application tailpipe, I made a simple offset bracket to bring the rear tailpipe hanger into line with the new tailpipe. This plate uses the frame bracket studs and original flex mount to place the clamp in the correct position. The clamp aligns and holds the tailpipe where I want it. As Borla updates the cat-back kit to fit the late XJ Cherokee, these needs will be considered for the kit.

Here is the Borla header in place. With a superior design that is built to last significantly longer than the stock tubular steel manifold, the header fits well. Despite the considerable work involved in replacing a 4.0L exhaust manifold, the properly engineered Borla header is no more difficult to install than the stock manifold.

With the system installed, Borla and Random Technology components make a neat, unrestricted exhaust package. Borla's header and connector pipe will add horsepower and fuel efficiency. The cat and Borla cat-back systems contribute further to engine performance and breathing. Borla's low-restriction muffler sets a performance tone to the exhaust. Clearly, this engine now breathes better!

The distinctive Borla tailpipe signifies quality, performance, and fuel-efficiency enhancements. In today's four-wheeling environment, these are key concerns. One look at the stock XJ, YJ, or TJ exhaust manifold and system, and you'll quickly consider the Borla alternative. For the Project XJ TrailRunner, a multipurpose 4x4, the gains in torque, horsepower, and gas mileage make this installation highly worthwhile.