Device and technical description 4.4L (Discovery 3)

4.4L V8 Exhaust System Layout

Item name	Spare part catalog number	Description
1	-	Manifold mounting flange to front section
2	-	Front Heated Oxygen Sensor Installation Location
3	-	Catalytic converter
4	-	Rear Heated Oxygen Sensor Installation Location
5	-	Right front section to rear section mounting flange
6	-	Rubber support (5 pcs.)
7	-	Front muffler
8	-	Central muffler
9	-	Rear muffler
10	-	Clamp for fastening the left front section to the rear section
11	-	Left exhaust manifold
12	-	Right exhaust manifold

General information

The 4.4L V8 exhaust system components are made from stainless steel and come in three separate assemblies. The left and right front sections contain the catalytic converter, while the rear section contains the front muffler, center muffler, and two rear mufflers.

The system is secured to the underbody by five rubber mounts which are mounted on mild steel hanger brackets welded to the system. The rubber mounts are mounted to the corresponding hanger brackets which are welded to the underbody. The system generally runs along the left side member, then splits in two near the rear axle differential and exits on both sides of the rear body.



Spare parts are supplied for repair of the exhaust system. The recesses on the rear section between the central and rear mufflers indicate the cutting point for replacing the rear mufflers or the front section. The spare section is attached to the cutting point using a bushing and two clamps.

Front section

Both front sections have a welded flange with two holes for mounting bolts to the left and right exhaust manifolds. A conical seat in the flange and a cone on the exhaust manifold are used to seal the flange.

The flange is welded into a short straight pipe, which in turn is welded into the catalytic converter housing. A threaded boss is welded above the hole in the pipe for mounting the front heated oxygen sensor (HO2S).

The neutralizer outlet pipe in the left front section is a pipe with a diameter of 55 mm and a wall thickness of 1.5 mm, welded to the casing of the catalytic converter. The rear end of the outlet pipe is inserted into the socket of the rear section of the exhaust pipe. A clamp is used to compress the joint.

The outlet pipe of the neutralizer in the right front section is a pipe with a diameter of 55 mm and a wall thickness of 1.5 mm, welded to the housing of the catalytic converter. The rear part of the pipe under the gearbox is bent to the left, and then bends again and runs parallel to the left pipe. A flange with two holes for studs on the rear section, to which the pipe is attached with nuts, is welded into the rear part of this pipe. A metal gasket is used to seal the joint between the flanges of the front and rear sections.



Threaded bosses are welded above the holes in the outlet pipes of the right and left neutralizers for installing rear heated oxygen sensors (HO2S).

Rear section

The rear section has a short pipe with a diameter of 55 mm and a wall thickness of 1.5 mm, flared to an internal diameter of 55 mm, into which the left front section is inserted. The pipe is welded to the front muffler housing assembly. A second short pipe with a diameter of 55 mm and a wall thickness of 1.5 mm has a welded flange with studs for fastening the flange to the right front section. The pipe is also welded to the front muffler housing assembly.

The front muffler is a single-layer cylinder with two welded end plates and has a volume of 6.4 liters. (390.5 in³). Inside the muffler there are partitions and perforated pipes, which reduce noise when exhaust gases pass through the muffler. A suspension bracket for installing a rubber support is welded to the front part of the muffler.

To connect to the central muffler, the front muffler has two short outlet pipes with a diameter of 55 mm and a wall thickness of 1.5 mm.

Central muffler with a volume of 25.2 l (1538 in³) the muffler consists of two stamped stainless steel shells welded together. Inside the muffler there are partitions and perforated pipes that reduce noise when exhaust gases pass through the muffler. A suspension bracket for installing a rubber support is welded to the right front part of the muffler.

The muffler has two outlet pipes with a diameter of 60 mm and a wall thickness of 1.5 mm, bent to bend around the elements of the rear suspension.



Each of the exhaust pipes is welded to the rear mufflers. The exhaust pipes have hanging brackets for installing rubber supports.

A suspension bracket for mounting a rubber mount is welded to the front of each rear muffler. The muffler is a circular cylinder with a tubular partition lined with fiberglass to improve noise absorption. The volume of each muffler is 2.7 liters. (165 inches³)

Each muffler has a 60mm diameter outlet pipe with a wall thickness of 1.2mm. Each outlet pipe is curved downwards to direct exhaust gases away from the rear of the car.

Catalytic converter

The engine management system provides precise metering of fuel supply to the combustion chambers, which ensures the most efficient use of fuel and reduces toxic emissions.

To further reduce the carbon monoxide and hydrocarbon content in the exhaust gases, a catalytic converter is integrated into the front exhaust manifold. In the catalytic converter, the exhaust gases pass through honeycomb ceramic elements with a special surface treatment ("washcoat"). The "washcoat" layer increases the surface area of the ceramic element walls by approximately 7,000 times. A coating is applied to the "washcoat" layer, which contains metals that are active components for converting toxic substances into inert ones. These metals oxidize the carbon monoxides and hydrocarbons in the exhaust gases and thus convert them into carbon dioxide and water, respectively.