MARINE EXHAUST MANIFOLD

Field of the Invention

The present invention relates to a marine exhaust manifold and especially but not exclusively to a stainless steel marine exhaust manifold for use in a boat with a petrol or diesel engine.

Background of the Invention Marine vessels are often provided with internal

V6 or V8 petrol or diesel internal combustion engines which have exhaust runners running from an engine head into a collector for which exhaust gases are forced by the action of an engine and from which exhaust gases are piped away from the engine by an exhaust pipe. Typically, the connectors are cast iron and provide a chamber which merely receives gas from the exhaust runners. The exhaust gas is expelled from the chamber through the exhaust pipe by the positive pressure supplied by the engine forcing gas into the chamber of the collector. Typically, the exhaust runners of a four cylinder engine (or four cylinders of an eight cylinder engine) are configured as two adjacent rows each of two pipes, so that the exhaust runners may be considered to enter the collector in a square configuration. This makes fitting of a water jacket to cool the exhaust system relatively convenient compared to having the exhaust runners enter the collector in a more spread out configuration. The inventor has realised that the above described prior art arrangement of exhaust runners, collector and exhaust pipe leaves room for improvement in assisting effective functioning of marine engines.

Summary of the Invention According to a first aspect of the present invention, there is provided a marine exhaust manifold comprising:

a collector for receiving exhaust gases from an engine; at least three exhaust runners for conducting exhaust as from said engine to said collector; and a cooling jacket which at least partially encloses said collector and exhaust runners so that a fluid within the cooling jacket can act to cool said collector and exhaust runners; wherein each of said at least three exhaust runners has a gas outlet in the collector and wherein the gas outlets ends of the at least three exhaust runners are provided in a substantially single plane, said plane being substantially parallel to the direction of expulsion of the exhaust gas into the collector. Preferably/ the gas outlet ends of the at least three exhaust runners are provided substantially in a line.

Preferably, at least one exhaust runner is adapted to expel exhaust gas into the collector so that the expelled exhaust gas is, in use, forced across the gas outlet end of at least one other exhaust runner in order to thereby create a pressure drop within said at least one other exhaust runner.

Preferably, the marine exhaust manifold comprises four exhaust runners, which comprise two sets of the exhaust runners and wherein each exhaust runner of a set is adapted to expel exhaust gas into the collector so that the expelled exhaust has is, in use, forced across the gas outlet end of the other exhaust runner of said set in order to thereby create a pressure drop within said other exhaust runner of said set.

Preferably, the marine exhaust manifold comprises three and only three exhaust runners and wherein each of the exhaust runners is adapted to expel exhaust gas into the collector so that the expelled exhaust has is, in use, forced across the gas outlet ends of the other exhaust runners in order to thereby create a pressure drop within

said other exhaust runners.

Preferably, at least one exhaust runner gas outlet and is shaped other than as a radial section of the exhaust runner. Preferably _/ wherein at least one exhaust runner gas outlet end is shaped as a first part which corresponds to a radial sectional surface of the exhaust runner and a second part comprising a non-radial section of the exhaust runner. Preferably, the cooling jacket is a fluid filled jacket having at least one inlet, and at least one outlet in fluid connection with the inlet, in order to allow a fluid to flow through the jacket.

Preferably, the cooling jacket is a water jacket having at least one inlet and at least one outlet in fluid connection with the inlet, in order to allow water to flow through the jacket.

Preferably, the marine exhaust manifold comprises at least one connection level, at or adjacent an exhaust gas inlet end of one or more exhaust runners, for connection to an engine head.

Preferably, a wall portion of the collector is welded to a external wall portion of each of the exhaust runners . Preferably, wherein the marine exhaust manifold is made substantially from stainless steel.

Preferably, the marine exhaust manifold is provided in electrically conducting contact with an element which sacrificially corrodes, thereby protecting the marine exhaust manifold from corrosion.

One preferred embodiment of a marine exhaust manifold has four, and only four, exhaust runners.

According to a second aspect of the present invention there is provided a marine exhaust manifold comprising: a collector for receiving exhaust gases from an engine;

at least two exhaust runners for conducting exhaust gas from said engine to the collector; and a cooling jacket which at least partially encloses said collector and exhaust runners so that a fluid within the cooling jacket can act to cool said collector and exhaust runners; wherein at least one exhaust runner is adapted to expel exhaust gas into the collector so that the expelled exhaust gas is, in use, forced across the gas outlet end of at least one other exhaust runner in order to thereby create a pressure drop within said at least one other exhaust runner.

Preferably, there are provided at least three exhaust runners, and the gas outlet ends of the at least three exhaust runners are provided substantially in a substantially single plane, said plane being substantially parallel to the direction of expulsion of the exhaust gas into the collector.

Preferably, there are provided at least three exhaust runners, and the gas outlet ends of the at least three exhaust runners are provided substantially in a line.

In one preferred embodiment a marine exhaust manifold comprises four exhaust runners, which comprise two sets of exhaust runners and wherein each exhaust runner of a set is adapted to expel exhaust gas into the collector so that the expelled exhaust has is, in use, forced across the gas outlet end of the other exhaust runner of said set in order to thereby create a pressure drop within said other exhaust runner of said set.

In one preferred embodiment a marine exhaust manifold comprises three and only three exhaust runners and wherein each of the exhaust runners is adapted to expel exhaust gas into the collector so that the expelled exhaust has is, in use, forced across the gas outlet ends of the other exhaust runners in order to thereby create a pressure drop within said other exhaust runners.

Preferably at least one exhaust runner gas outlet is shaped other than as a radial section of the exhaust runner.

Preferably at least one exhaust runner gas outlet end is shaped as a first part which corresponds to a radial sectional surface of the exhaust runner and a second part comprising a non-radial section of the exhaust runner.

At least one exhaust runner gas outlet end may be shaped by an end portion of the exhaust runner which is angled aligned at an angle other than 90 degrees to the axis of the exhaust runner at said end portion thereof.

Said angle may be approximately 60 degrees to the away axis of the exhaust runner at said end portion thereof.

Preferably the cooling jacket is a water jacket having at least one inlet, and at least one outlet in fluid connection with the inlet, in order to allow water to flow through the jacket. Preferably the marine exhaust manifold comprises at least one connection member, at or adjacent an exhaust gas inlet end of one or more exhaust runners, for connection to an engine head.

Preferably a wall portion of the collector is welded to an external wall portion of each of the exhaust runners .

Preferably a wall portion of the collector is aligned generally parallel to, and is substantially contingent with, a wall potion of an exhaust runner entering the collector.

Preferably the angle between said one exhaust runner at its outlet end, and said at least one other exhaust runner at its outlet end is between approximately 20 and approximately 70 degrees. Preferably the angle between said one exhaust runner at its outlet end, and said at least one other exhaust runner at its outlet end is between approximately

35 and approximately 55 degrees.

Preferably the angle between said one exhaust runner at its outlet end, and said at least one other exhaust runner at its outlet end is approximately 45 degrees. Preferably the marine exhaust manifold is made substantially from stainless steel.

Preferably the marine exhaust manifold is provided in electrically conducting contact with an element which sacrificially corrodes, thereby protecting the marine exhaust manifold from corrosion.

In one embodiment a marine exhaust manifold has four, and only four, exhaust runners.

According to a third aspect of the present invention there is provided a marine exhaust manifold comprising: a collector for receiving exhaust gases from an engine; at least two exhaust runners for conducting exhaust gas from said engine to the collector; and a cooling jacket which at least partially encloses said collector and exhaust runners so that a fluid within the cooling jacket can act to cool said collector and exhaust runners; and wherein the marine exhaust manifold is provided in electrically conducting contact with an element which sacrificially corrodes, thereby protecting the marine exhaust manifold from corrosion.

Preferably the element which sacrificially corrodes is replaceably retained in a socket provided in the marine exhaust manifold.

Preferably the element which sacrificially corrodes is metallic.

Preferably the element which sacrificially corrodes is made at least partially from zinc. Preferably the element which sacrificially corrodes is a sacrificial anode.

Preferably the marine exhaust manifold is formed

substantially from a ferrous metal.

Preferably the marine exhaust manifold is formed substantially from stainless steel.

A. marine exhaust manifold in accordance with any one of the above aspects may beneficially include or incorporate features recited in relation to one or more other aspects.

Brief description of the drawings Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a schematic side elevation of an embodiment of a marine exhaust manifold with four exhaust runners, and including a cooling jacket;

Figure 2 is a schematic elevation of the embodiment of Figure 1, from the other side, showing some internal detail, and with the cooling jacket omitted;

Figure 3a is a schematic partial vertical cross- sectional view of a part of the embodiment of Figure 2;

Figure 3b is a schematic partial horizontal cross-sectional view of a part of the embodiment of Figure 2, showing the exhaust runners from above;

Figure 4 is a schematic illustration of an alternative embodiment, having three exhaust runners, with the water jacket omitted; and

Figure 5 is a schematic partial vertical cross- sectional view of a part of the embodiment of Figure 4.

Description of Preferred Embodiments

With reference to Figure 1, an embodiment of a marine exhaust manifold comprises an exhaust manifold system generally designated 1. The exhaust manifold system 1 is for use in a boat (and it will be appreciated that the word "marine" used herein is not intended to exclude fresh water applications) . The exhaust manifold system 1 is suitable for use in conveying exhaust gases

from an engine head having four exhaust gas outlet ports, such as a one bank of cylinders of an eight cylinder petrol or diesel engine.

The exhaust manifold system 1 comprises first, second, third and fourth exhaust runners 2,4,6,8, respectively, a collector 20, an exhaust pipe 30 and a water jacket 40. The exhaust runners 2,4,6,8 are adapted to connect an engine head (not shown) to the exhaust gas collector 20 in order that exhaust gas expelled from the engine head can be channelled to the collector 20. From the collector 20 the exhaust gases flow to the exhaust pipe 30, connected to the collector 20, from which the exhaust gas can be released, for example into a further part of an exhaust system, or into the atmosphere. The water jacket 40 encloses the exhaust runners

2,4,6,8, collector 30 and part of the exhaust pipe 30.

In most applications the exhaust manifold system 1 will be generally vertically oriented, so that exhaust gases flow generally upwards from the engine head through the exhaust runners 2,4,6,8, and generally upwards through the collector 30 into the exhaust pipe 30. For the purposes of this description this typical generally vertical orientation will be adopted, although this is not intended to exclude the possibility of other orientations. The water jacket 40 has a water jacket inlet 42, which in this embodiment is towards the bottom of the exhaust manifold system 1 (adjacent exhaust gas inlet ends of the exhaust runners) and a plurality of water jacket outlets 44 which in this embodiment are provided towards the top of the water jacket 40, which is located part way along the exhaust pipe 30. It will be appreciated that fresh or salt water may be forced through the water jacket 40 from the water jacket inlet 42 to the water jacket outlets 44 and that this water flow will effect cooling of the exhaust runners 2,4,6,8, collector 20 and exhaust pipe 30. It will also be appreciated that other coolants could be used if desired (although the water in which the is a

convenient and abundant option) and that even use of a cooling jacket using a gas as a coolant is not considered to be beyond the scope of the invention.

In the preferred embodiment the exhaust runners 2,4,6,8, collector 20, exhaust pipe 30 and cooling jacket 40 are all made of marine grade stainless steel and the exhaust manifold system 1 as a whole is fabricated by welding the various parts together to provide a single unit. The welded unit of the preferred embodiment is considerably lighter and more corrosion resistant than typical exhaust systems which are formed at least partly from cast iron or cast alloy components. In the illustrated embodiment, a replaceable sacrificially corroding anode element in the form of a replaceable zinc element 46 is located in a threaded aperture 47 of the water jacket 40, and is provided in order to further reduce corrosion of the exhaust manifold system 1. Provision of the threaded aperture 47 for this purpose allows easy replacement of the sacrificial anode. Of course, any suitable sacrificially corroding material or element could be used, but an unit made of zinc is currently preferred.

In the embodiment of Figure 1, the part of the exhaust pipe 30 distal from the connector 20 has a downturned end portion 32 terminating in an exhaust pipe outlet 34. The downturned end portion 32 helps avoid water entering the exhaust manifold system 1 (and the engine) via the exhaust pipe outlet 34.

Figure 2 shows the exhaust manifold system 1 of Figure 1 from the opposite side, illustrates interior detail of the parts of the exhaust runners 2,4,6,8 which are inside the connector 20, and omits the water jacket 40 for convenience. As can be seen from Figure 2, each of the first, second, third and fourth exhaust runners 2,4,6,8 is connected to a bottom plate 10 which is adapted to be securely attached to an engine head by bolts (not shown) which, in use, pass through apertures 11 provided

in the bottom plate 10. The exhaust runners 2,4,6,8 have respective inlet ends 3,5,7,9 which in use are sealed to the exhaust ports (not shown) of the engine head.

The exhaust runners 2,4,6,8 extend between the bottom plate 10 and the collector 20 and convey exhaust gases from the respective inlet ends 3,5,7,9 to respective outlet ends 12,14,16,18 of the exhaust runners 2,4,6,8, which are sealed in the collector 20. The exhaust gases are ejected, by the exhaust pressure provided by the engine, from the outlet ends 12,14,16,18 of the exhaust runners 2,4,6,8, into the collector 20.

The first exhaust runner 2 is connected to the second exhaust runner 4 by a first weld 13 adjacent the outlet ends 12 , 14 of the first and second exhaust runners . The second exhaust runner 4 is connected to the third exhaust runner 6 by a second weld 15 adjacent the outlet ends 14,16 of the second and third exhaust runners. The third exhaust runner 6 is connected to the fourth exhaust runner 8 by a third weld 17 adjacent the outlet ends 16,18 of the third and fourth exhaust runners.

The outlet ends 12,14,16,18 of the exhaust runners 2,4,6,8, are shaped and positioned so that as each expels exhaust gas into the collector 20, the expelled exhaust gas is blown over the outlet end of a neighbouring exhaust runner. This amounts to blowing a rapidly moving moving fluid across the end of a pipe (the neighbouring exhaust runner) which creates a pressure drop, or partial vacuum, in the said neighbouring exhaust runner. This pressure drop enhances flow of exhaust gases from the engine into the exhaust runner in which the pressure drop has occurred, effectively reducing back pressure, allowing the engine to *breathe' more efficiently, and thereby increases the power and torque output of the engine. The shapes and relative positions of the outlet ends 12,14,16,18 of the exhaust runners 2,4,6,8 will be more fully described below, with reference to Figures 3a and 3b.

The collector 20 may be regarded as having an exhaust gas inlet end and an exhaust gas outlet end. The exhaust gas inlet end of the collector 20, where the collector 20 connects to the exhaust runners 2,4,6,8 is somewhat elongate, as the exhaust runners 2,4,6,8 are arranged in a line where they enter the collector 20. The casing of the collector 20 is welded to the first to fourth exhaust runners 2,4,6,8 at the regions illustrated schematically on Figures 2, 3a and 3b and designated 22,24,26,28, respectively. It will be appreciated that in the illustrated embodiment the exhaust runners extend into the collector 20 rather than terminating in ports in the wall of the collector. In a preferred embodiment the exhaust runners extend approximately 10 to 15 mm (half an inch) into the collector 20. A preferred method of construction is to form the collector as two separate lateral halves which each welded to each of the exhaust runners, to the exhaust pipe, and to each other so that the collector provides a unit which is sealed except for the entrances and exit corresponding to the exhaust runners and exhaust pipe respectively. The exhaust gas outlet end of the collector 20, where the collector 20 connects to the exhaust pipe 30 is generally circular in cross section, as the exhaust pipe is generally circular in cross section. The casing of the collector 20 is welded to the exhaust pipe 30 at the region illustrated schematically on Figure 2 and designated 29.

Referring now to Figures 3a and 3b, it can be seen that in this embodiment the first and second exhaust runners 2, 4 form a first pair (or set) in which each of the exhaust runners of the first pair expels exhaust gas (as indicated by the block arrows) over the outlet of the other exhaust runner in the pair. The outlet ends 12, 14 are angled at about 45 degrees relative to each other. The outlet end 12 of the first exhaust runner 2 is simply an end of the pipe which forms the first exhaust runner 2, truncated perpendicular to the axis of the pipe. However

in order to enhance the interaction, the outlet end 14 of the second exhaust runner 4 is not simply truncated perpendicular to the axis of the pipe which forms the second exhaust runner 4, since this would provide an considerably non-uniform effect across the width of the outlet end. Instead the outlet end 14 is provided with an angled portion, 14b which is angled at about 45 degrees to the axis of the pipe (the second exhaust runner) to correspond generally to the direction of movement of the exhaust gas expelled from the first exhaust runner 2.

Although the angled portion 14a could be provided so that it extends across the entire width of the outlet end 14 of the second exhaust runner 4, it has been found particularly effective to have the angled portion 14a extend from the side adjacent the first exhaust runner across a little more than half the width, and to have a square cut portion 14b (ie a portion that is truncated perpendicular to the axis of the second exhaust runner 4) extend the remainder of the width of the outlet end 14 of the second exhaust runner 4. It is believed that this configuration reduces undesirable deflection or disturbance, and is therefore advantageous (over having the angled portion, angled to correspond generally to the direction of movement of the passing exhaust gas, extend across the entire width of the outlet end 14 of the second exhaust runner 4) . Other configurations are possible. For example having a continuous angled section extend across the entire width, but at an angle ten or twenty degrees offset from the direction of movement of the passing exhaust gas (or the orientation of the exhaust runner outlet expelling that gas) could also be effective.

It will be appreciated that the outlet ends 16, 18 third and fourth exhaust runners 6,8 are configured similarly (but in mirror image) to the configuration of the outlet ends 12, 14 of the first and second exhaust runners 2,4. In particular, the outlet end 16 of the third exhaust runners 6 has a an angled portion, 16b which is

angled at about 45 degrees to the axis of the pipe (the third exhaust runner) to correspond generally to the direction of movement of the exhaust gas expelled from the fourth exhaust runner 2. It is known from high school physics that a rapidly moving fluid exerts a lower pressure than a slow moving fluid. It will therefore be evident to the addressee that expelling exhaust gas from one exhaust runner across the outlet of another exhaust runner will result in a pressure drop, or partial vacuum, in that other exhaust runner. It will also be evident that having a low pressure, or partial vacuum, in an exhaust runner facilitates expulsion of exhaust gas from a cylinder of an engine into that exhaust runner. Facilitated expulsion of exhaust gas is known to enhance engine power output. The angle at which exhaust gas is blown across an outlet is important in creating the pressure drop. If the angle is too small (less than about 15 or 20 degrees) , then the gas cannot really be considered to be blown "across" the outlet, and the desired effect is not inadequate or nonexistent. If the angle is too great (and in particular, if it is greater than 90 degrees) the gas will tend to be blown into the outlet rather than across it, with the consequence of increasing, rather than decreasing the pressure in the exhaust runner. It is therefore desirable to use an angle of between about 20 degrees and about 70 degrees, with angles of between 35 and 55 degrees normally being preferred, and angles of about 45 degrees being particularly preferable. It will be appreciated that expulsion of exhaust gases from the exhaust runners into the collector will be cyclical, and that (for most, if not all, internal combustion engines) exhaust gas will be expelled first from one exhaust runner, then each other exhaust runner until a full cycle has been performed, at which point the cycle will begin again. Of course, the full engine cycle may take only a very small fraction (perhaps between one

twentieth and one hundredth) of a second. Thus, in the preferred embodiment each exhaust runner is provided with a pressure drop a tiny fraction of a second before the point in the engine cycle when exhaust gas is to be expelled from the engine into that exhaust runner. It will thus be understood that expulsion of exhaust gas from the engine into the exhaust manifold is facilitated.

As illustrated best in Figure 3a _# the walls of the collector 20 are angled to be generally continuous with the directions in which exhaust gas is expelled from the outlet ends 12,14,16,18 of the exhaust runners. This assists in avoiding unduly disturbing the flow of exhaust gas through the collector 20.

In the preferred embodiment the exhaust runners each have a diameter of about 4.5cm (1.75 inches) and the collector 20 has a cross sectional area, at its inlet (bottom) end, generally corresponding to the sum of the cross sectional areas of the four exhaust runners, ie about 250 cm ² (about 38 square inches) . The exhaust pipe 30 has a diameter of about 7.5 cm (3 inches) and the collector 20 has a cross sectional area, at its outlet (top) end, corresponding to the cross sectional area of the exhaust pipe, ie about 176 cm ² (about 28 square inches) . This represents a collector shape which tapers fairly smoothly from the inlet end to the outlet end, and which does not suddenly and discontinuously increase the cross sectional flow area. This is in contrast to typical prior art exhaust gas collection chambers, in which exhaust runners are caused to expel exhaust gas into a chamber with a cross sectional flow area much greater than that of the runners, thus causing rapid deceleration of the exhaust gas. In the described embodiment the exhaust gas is not substantially decelerated by entry to, or passage through, the collector, so the speed of the exhaust gas is maintained, allowing the exhaust gas expelled from outlets of exhaust runners to create a pressure drop in one or more nearby exhaust runners. As

illustrated in Figures 1 and 3b, the walls of the collector 20, are somewhat contoured in the region 27 close to where the exhaust runners enter the collector, so that the contoured side parts of the collector wall may be regarded as having a function of guiding the exhaust gas expelled by the exhaust runners between the inlet and outlet parts of the collector. This may assist in promoting smooth flow of the exhaust gas through the collector 20. Figure 4 illustrates an alternative embodiment of a marine exhaust manifold comprising an exhaust manifold system generally designated 101. The exhaust manifold system 101 is similar in many respects to the exhaust manifold system 1 of Figures 1 to 3b, but differs in that it is suitable for use in conveying exhaust gases from an engine head having three (rather than four) exhaust gas outlet ports, such as a one bank of cylinders of a six cylinder petrol or diesel engine.

The exhaust manifold system 101 comprises first, second and third exhaust runners 102,104,106, respectively, a collector 120, an exhaust pipe 130 and a water jacket (which, for convenience, is not shown, since the structure and function of the water jacket can easily be appreciated by analogy with the water jacket 40 of the exhaust manifold system 1, described above) . The exhaust runners 102,104,106, in use, connect an engine head (not shown) to the exhaust gas collector 120 in order to channel exhaust gas, expelled from the engine head, to the collector 120. From the collector 120 the exhaust gases flow to the exhaust pipe 130.

The exhaust runners 102,104,106, collector 120, exhaust pipe 130 and cooling jacket are all made of marine grade stainless steel and the exhaust manifold system 101 as a whole is fabricated by welding the various parts together to provide a single unit. A replaceable sacrificially corroding anode element, preferably in the form of a replaceable zinc element, is provided.

preferably located in a threaded aperture of the water jacket 40, to help reduce corrosion of the exhaust manifold system 101.

Each of the first, second and third exhaust runners 102,104,106, is connected to a bottom plate 110 which is adapted to be securely attached to an engine head by bolts (not shown) passing through apertures 111. The exhaust runners 102,104,106 have respective inlet ends 103,105,107 which in use are sealed to the exhaust ports (not shown) of the engine head.

The exhaust runners 102,104,106 convey exhaust gases from the respective inlet ends 103,105,107 to respective outlet ends 112,114,116 of the exhaust runners in the collector 20. The first exhaust runner 102 is connected to the second exhaust runner 104 by a first weld 113 adjacent the outlet ends 112,114 of the first and second exhaust runners, and the second exhaust runner 104 is connected to the third exhaust runner 106 by a second weld 115 adjacent the outlet ends 114,116 of the second and third exhaust runners.

The outlet ends 112,114,116 of the exhaust runners 102,104,106 are shaped and positioned so that as each expels exhaust gas into the collector 20, the expelled exhaust gas is blown over the outlet ends of the other exhaust runners, which in use creates a pressure drop, or partial vacuum, in those exhaust runners, enhancing flow of exhaust gases from the engine into the exhaust runners and thereby increasing the power and torque outputs of the engine . The shapes and relative positions of the outlet ends 112,114,116 of the exhaust runners 102,104,106 are illustrated in Figure 5. The angle between the axis of the outlet 114 of the second exhaust runner 104 and the outlets 112, 116 of each of the first and third exhaust runners 102, 106 is about 22 to 28 degrees, and the angle between the axis of the outlet 112 of the first exhaust runner 102 and the outlet 116 of the third exhaust runner

106 is about 45 to 55 degrees. Like the embodiment 1 of Figures 1 to 3b the walls of the collector 120 help smoothly guide the gas flow. Unlike the embodiment 1 of Figures 1 to 3b it is adequate for each outlet to be substantially perpendicular to the respective pipe axis . The preferred embodiments thus provide exhaust manifolds which use the available exhaust gas pressure in an exhaust runner to create a pressure drop in one or more neighbouring exhaust runners, facilitating expulsion of exhaust gases from the engine. Tests have indicated a power increase of around 25 horsepower, and an increase in maximum torque of about 40 Nm can be obtained by replacing a conventional marine exhaust manifold with the manifold illustrated in Figures 1 to 3b, on a V8 engine. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, ie. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Variations and modifications can be made in respect of the invention described above and defined in the following statements of claim.