TECHNICAL FIELD [0001] The present subject matter relates to an internal combustion engine for a two-or three-wheeled vehicle and more particularly, relates to an exhaust system of the internal combustion engine.
BACKGROUND [0002] Generally, in a motor vehicle, an internal combustion (IC) engine includes an intake system for supplying air-fuel to the IC engine. An exhaust system connects the internal combustion engine to a muffler of the vehicle. Generally, the exhaust gas generated in a combustion chamber of the IC engine is discharged to the atmosphere. In the motor vehicle, an exhaust port of the IC engine is connected to an exhaust pipe of the exhaust system enabling discharge of the combusted gases to the atmosphere. Generally, the position of the exhaust port is subject to specific orientation of mounting of the engine on to the vehicle which has layout & packaging challenges associated with it. Moreover, to effectively reduce emissions from the exhaust gases that are exiting out of the engine, it is important to position a catalytic converter as close as possible to the exhaust port. However, in most motor vehicles, optimally positioning the catalytic converter also becomes a challenge, which is mainly due to the layout constraint of the motor vehicle.
BRIEF DESCRHTION OF THE DRAWINGS [0003] The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to reference like features and components.
[0004] Fig. 1 depicts a right-side view of an exemplary two-wheeled vehicle, in accordance with an embodiment of the present subject matter. [0005] Fig. 2 illustrates a right-side view of an internal combustion engine including its exhaust system, in accordance with the embodiment as depicted in Hg. 1. ,

[0006] Fig. 3 (a) illustrates a cross-sectional front view of a cylinder head
assembly of the internal combustion engine, in accordance with an
implementation of the present subject matter.
[0007] Fig. 3 (b) illustrates a cross-sectional view of exhaust port taken at the
section Z-Z of the engine depicted in Fig. 3 (a), in accordance with one
implementation of the present subject matter.
[0008] Fig. 3 (c) illustrates a cross-sectional view of exhaust port taken at the
section XX-XX of the engine depicted in Fig. 3 (a), in accordance with one
implementation of the present subject matter.
[0009] Fig. 3 (d) illustrates a cross-sectional view of exhaust port taken at the
section YY-YY of the engine depicted in Fig. 3 (a), in accordance with one
implementation of the present subject matter.
[00010] Fig. 4 (a) illustrates a cross-sectional view of the exhaust system of the
internal combustion engine, in accordance with a first embodiment of the present
subject matter.
[00011] Fig. 4 (b) illustrates a cross-sectional view of the exhaust system of the
internal combustion engine, in accordance with a second embodiment of the
present subject matter.
[00012] Fig. 5 illustrates a cross-sectional view of the exhaust port of the
internal combustion engine, in accordance with another embodiment of the
present subject matter.
[00013] Fig. 6 (a) depicts a characteristic curve of exhaust gas temperature in
the exhaust system of the internal combustion engine, in accordance with an
embodiment of the present subject matter.
[00014] Fig. 6 (b) illustrates a cross-sectional view of a conventional exhaust
system depicting the intersection of the exhaust port and the exhaust pipe.
[00015] Fig. 6 (c) illustrates a cross-sectional view of the exhaust system
depicting the intersection of the exhaust port and the exhaust pipe, in accordance
with an embodiment of the present subject matter.

[00016] Fig. 7 depicts a characteristic curve of engine torque of the internal
combustion engine, in accordance with an embodiment of the present subject
matter.
[00017] Fig. 8 depicts a method of manufacturing of the cylinder head in
accordance with an embodiment of the present subject matter.
[00018] Fig. 9 illustrates a cross-sectional view of the cylinder head assembly of
the present subject matter depicting an intake port passage and an exhaust port
passage with an integrated sand core disposed therein.
DETAILED DESCRIPTION
[00019] Generally, the internal combustion engine having 4-stroke cycle is popular. The 4-stroke cycle starts with an intake stroke and ends at an exhaust stroke. Due to combustion of air-fuel mixture that gets compressed during compression stroke and then combusted thereby resulting in the power stroke. The combusted gases are transmitted to the exhaust system from the cylinder head. In general, the performance of .the vehicle depends on various parameters that include the air-fuel mixture that is supplied during intake. However, in certain conditions, the performance of the engine is also dependent on the nature of the exhaust gases being transmitted out. For example, contaminants in the combustion chamber created during combustion process affect lubrication properties in the combustion chamber. This in turn, increases friction, which affects the performance of the vehicle.
[00020] In addition, an.upstream end of the exhaust pipe is connected to the exhaust port of the cylinder head. The muffler is either disposed towards one lateral side of the vehicle or is disposed along a vehicle center & typically downstream of the engine with exhaust pipe being routed between the two so as to enable discharge of exhaust gases towards downstream end of the vehicle., the upstream end of the exhaust pipe being connected to the cylinder head assembly includes a bend portion to connect to the exhaust port, which is generally disposed either on a front facing side of the cylinder head or on a downward facing side of the cylinder head. This typically requires complex routing of the exhaust pipe

with a bent portion. Additionally, effective sealing at the joining portion or interface of the exhaust pipe with the cylinder head assembly puts high demand on the profile as well as the geometric accuracy of the interface components ■ which is critical to ensure leak proof system. Also, the operating temperatures (thermal loads) are high in close vicinity of the cylinder head owing to its' proximity to the combustion chamber & this further adds to the challenges of having an effective joint at the interface. The manufacturing of the bent pipe is also complex & difficult involving manufacturing challenges like spring-back effect of the material, bend folds, warping etc. Achieving the bent profile often necessitates multi-stage process making it not very economical to meet the geometric accuracy.
[00021] Moreover, any gaps arising at the joint interface with the cylinder head' assembly can lead to undesirable leakage, performance loss, noise, contamination & poor durability cum life of the entire power train system as a whole. Additionally, this bent portion further affects the flow of exhaust gas, therethrough, which affects the performance of the engine. Also, presence of bent portion affects flow of exhaust gas creating resistance that adversely affects performance. Further, the exhaust gas may result in undesirable exhaust noise. Also, the structural strength of the exhaust pipe is low at the bent portion on the exhaust pipe since the bent portion undergoes wall thinning on the outward surface of the exhaust pipe at the bent portion. This can result in breakage or failure at the bent portion. Moreover, combination of manufacturing stresses & thermal loads on exhaust pipes tend to lead to rust especially at the upstream end portion resulting in failure of the exhaust pipe. It is also a common phenomenon that the complex profile of the exhaust pipe makes it cumbersome to dismantle . and service the engine assembly.
[00022] Generally, conventional engines are provided with cylinder head in which the exhaust port is provided on the side opposite to the intake port. In case of ports having circular cross-section, the diameter of the exhaust port and that of the intake port is decided based on the engine configuration and performance requirements. Alternatively, in case of ports having non-circular cross-section, for

example, of oval shape, the cross-sectional area of the exhaust port and that of the intake port is taken into consideration. For example, higher the swept volume of the engine, larger will be the diameter or cross-sectional area of the ports for taking in and throwing out that much amount of air fuel mixture into and from the combustion chamber of the engine. Most often than not, the diameter or cross-sectional area of the intake port(s) of the engine is larger than that of the exhaust " port(s). This is mainly due to the fact that during suction stroke, a large quantity of air fuel mixture has to be drawn in at not so significant pressure difference between the cylinder head and the atmosphere. On the other hand, the exhaust gases from the combustion chamber are sent out of the exhaust port, when the pressure difference between the cylinder head and the atmosphere is significant. In the process it is also essential to maximise the combustion efficiency to be able to generate maximum power as well as ensure minimum emissions. [00023] To this end, the conventionally known cylinder heads are provided with one or more exhaust ports having a diameter or cross-sectional area that gradually increases from the valve seat to the port outlet. Typically, exhaust pipes have a construction with its end connecting the exhaust po'rt flared out, i.e., the ends of the exhaust pipe joining the exhaust port region are flared out to be able to connect to the mounting flanges of the exhaust port. However, the diameter or cross-sectional area of the exhaust pipe at its joining face with the outlet of the exhaust port remains substantially lesser than the diameter or cross-sectional area of the outlet of the exhaust port. Such a construction was necessary to achieve the desired performance characteristics of the engine such as increase in low end torque; increase in exhaust gas velocity, without hampering the flow rate of the exha'ust gases.
[00024] Generally, providing a flaring at the joining face of the exhaust pipe made of sheet metal involves tedious machining processes and the resulting flaring also lacks consistency. Moreover, such generally known exhaust systems in which the exhaust port diameter or cross-sectional area gradually increases from the valve seat up to the joining face of the exhaust pipe, and having exhaust pipe whose diameter or cross-sectional area at the joining face is substantially

lesser than the outlet diameter or cross-sectional area of the exhaust port tends to face various other problems such as those mentioned in the preceding paragraphs, for example, absence of effective sealing at the joining portion or interface of the exhaust pipe with the cylinder head assembly, which puts high demand on the profile as well as the geometric accuracy of the interface components that prevents achieving a leak proof system, even though the flow rate of the exhaust gases and the desired performance of the engine is generally achieved. [00025] Typically, to minimize emissions the exhaust systems are provided with one or more catalytic converters for achieving desired emission control. To get best results it is imperative to achieve early light-off of such catalytic converters for improved performance output of the catalytic converters. Thus, conventionally known exhaust systems designed with capability, of achieving desired engine performance characteristics may still fall short of achieving optimal emission control. Further in known art close loop control systems with oxygen or lambda sensor are provided to further enhance emission control. However, such known systems suffer from high volumetric flow of exhaust gases rendering them to have to work with poor low end torque and other comprises as outlined in the subsequent paragraph.
[00026] Typical exhaust systems having exhaust port, whose diameter or cross-sectional area gradually increases up to the joining face with the exhaust pipe and the diameter or cross-sectional area of the exhaust pipe at the joining face being substantially lesser than the outlet diameter or cross-sectional area of the exhaust port, tends to reduce the velocity of the exhaust gases that reaches the one or more catalytic converters, which are disposed downstream in the exhaust pipe. This is because, the expanded outer cross-section of the exhaust port and the corresponding joining face of the exhaust pipe having a diameter or cross-sectional area substantially lesser than the outlet diameter or cross-sectional area of the exhaust port, tends to increase the pressure and flow rate, but results in reducing the velocity of the exhaust gases. The reduction in velocity of the exhaust gases mean the temperature of the exhaust gases reaching the one or more

catalytic converters also drops, which in most cases affects the early light-off of the catalytic converter.
[00027] Several attempts have been made in the past by providing a stepped exhaust passage in the exhaust port. However, such attempts have not been able to achieve the desired effect of increasing the efficiency of the catalytic converter without compromising the performance of the engine at certain operating points and without affecting the torque and power of the engine. For example, attempts have been made in the past to reduce exhaust resistance and improve the exhaust process by forming spirally twisted exhaust port, which causes the combusted exhaust gases to spirally circulate before being let out. However, such configurations were more viable in two-stroke engines where there are no valves. Moreover, attempting such a configuration in a four-stroke engine is costlier and not likely to yield the desired performance of the engine. Attempts have also been made to increase discharge efficiency of the exhaust gases in view of improving the overall .output of the .engine.-In-view -of-achieving such-an~objective7~the exhaust port was configured to include a combination of an inwardly swollen region and an outer venturi unit. However, such a construction of the exhaust port could result in increasing the pressure and a drop-in exit velocity of the exhaust gases for the sake of gaining an increased flow rate. On the contrary, the present subject matter is aimed at increasing the velocity of the exhaust gases, for which a pressure drop is created, the impending loss of flow rate is compensated by the profile of Lhe exhaust port, the chamfer angle of the reduced cross-section and the length of the land provided at the outlet face of the exhaust port of the present' subject matter.
[00028] Thus, there is a need for an internal combustion engine that is having exhaust system that addresses aforementioned and other short comings in the prior art. At the same time, the exhaust system should enable achieving an optimal emission control, improve the performance and offer reduced resistance for flow of exhaust gases, without affecting the engine torque and power. Further, the assembly and disassembly of the exhaust pipe for maintenance or otherwise should be made less cumbersome.

[00029] Hence, the present subject matter provides an exhaust system for an internal combustion engine including an exhaust system that is capable of improving the performance of the engine at specific operating points. [00030] Further, the present subject matter ensures that the problems faced in the existing art with respect to flaring of the exhaust pipe, which results in lack of consistency with respect to geometric accuracy of the interface components that prevents achieving a leak proof system, are overcome. The present subject matter • is aimed at achieving desired consistency of design of the exhaust system by largely reducing the variation in design. To achieve the above objectives, the present subject matter provides an exhaust system, in which the flow characteristics are transferred from the exhaust pipe and incorporated in the exhaust port, without compromising on the torque and power requirement of the engine.
[00031] In an implementation, the present subject matter provides increase in exhaust gas velocity for achieving early light-off of catalytic converters provided downstream of the exhaust pipe, especially in its cold phase. [00032] In an implementation, the present subject matter provides an internal combustion engine for a two-or-three-wheeled vehicle. In particular, the present subject matter provides a four-stroke internal combustion engine. More particularly, the present subject matter provides a four-stroke internal combustion ■ engine having a single cylinder. The internal combustion engine typically includes at least one cylinder head. The at least one cylinder head includes at least one intake port. A combustion chamber that receives intake charge from a fuel supply device through at least one intake port is provided. The cylinder head is also provided with at least one exhaust port capable of expelling combusted gases from the combustion chamber to atmosphere through an exhaust pipe of the vehicle. The engine assembly consists of at least one spark plug.
[00033] The at least one exhaust port has an upstream portion adjoining the combustion chamber and a downstream portion adjoining an inlet opening of the exhaust pipe. The downstream portion of the exhaust port has a first diameter or cross-sectional area substantially equal to a second diameter or cross-sectional

area of the inlet opening of the exhaust pipe at a joining face of the exhaust pipe with the exhaust port.
[00034] In one implementation, the exhaust port of the present subject matter has an intermediate portion disposed adjacent to the downstream portion. Further, the second diameter or cross-sectional area of the inlet opening of the exhaust pipe is approximately 1.10 to 1.20 times the first diameter or cross-sectional area of the downstream" portion of the exhaust port. In one implementation, the exhaust port has a first region connecting an upstream portion of the exhaust port and the intermediate portion and a second region connecting the downstream portion and the intermediate portion.
[00035] In an embodiment, the intermediate portion has a specific profile design of the exhaust port, for example, a reduced cross-section provided with a predetermined angle ranging from 3° to 20°. The reduced cross-section has an upstream diameter or cross-sectional area substantially greater than a downstream diameter or cross-sectional area.
[00036] Further, in one embodiment, the second region oTthe exhaust port"has a" _ length ranging approximately between 2.5 mm to 4 mm, while the first diameter ranges approximately between 15 mm to 25 mm.
[00037] In an implementation, the exhaust pipe includes at least one catalytic converter unit disposed at a predetermined distance from the exhaust port, for example, at a distance'of approximately between 175 mm to 300 mm from the reduced cross-section of the exhaust port. The exhaust pipe also includes an oxygen sensor disposed between the exhaust port and the catalytic converter unit. In an embodiment, the oxygen sensor is disposed substantially closer to the catalytic converter unit, for example at a distance of approximately between 15 mm to 20 mm upstream of the catalytic converter unit.
[00038] In - an implementation, the intermediate portion of the exhaust port receives at least one secondary air injection outlet conduit and in another embodiment, the exhaust port is provided with an exhaust gas recirculation conduit instead of at least one secondary air injection outlet conduit.

[00039] Further, in one implementation, the present subject matter provides an internal combustion engine for a two-or-three-wheeled vehicle. The internal combustion engine typically includes at least one cylinder head. The at least one cylinder head includes at least one intake port. A combustion chamber that receives intake charge from a fuel supply device through at least one intake port is provided. The cylinder head is also provided with at least one exhaust port capable of expelling combusted' gases from the combustion chamber to atmosphere through an exhaust pipe of the vehicle. The at least one exhaust port has an upstream portion adjoining the combustion chamber and a downstream portion adjoining an inlet opening of the exhaust pipe. The downstream portion of the exhaust port has a first diameter or cross-sectional area substantially lesser than a second diameter or cross-sectional area of the inlet opening of the exhaust pipe at a joining face of the exhaust pipe with the exhaust port. In an embodiment, the second diameter or cross-sectional area of the inlet opening of the exhaust .pipe is approximately 1.2 to 1.5 times the first diameter or cross-sectional area of the downstream portion of the exhaust port.
[00040] Furthermore, in one another implementation, the present subject matter provides an internal combustion engine for a two-or-three-wheeled vehicle. The internal combustion engine typically includes at least one cylinder head. The at least one cylinder head includes at least one intake port. A combustion chamber that receives intake charge from a fuel supply device through at least one intake port is provided. The cylinder head is also provided with at least one exhaust port capable of expelling combusted gases from the combustion chamber to atmosphere through an exhaust pipe of the vehicle. The at least one exhaust port has an upstream portion adjoining the combustion chamber and a downstream portion adjoining an inlet opening of the exhaust pipe. The downstream portion of the exhaust port has a first diameter or cross-sectional area substantially lesser than a second diameter or cross-sectional area of the inlet opening of the exhaust pipe at a joining face of the exhaust pipe with the exhaust port. The exhaust port has an intermediate portion disposed adjacent to the downstream portion. The exhaust port has a first region connecting the upstream portion of the exhaust port

and the intermediate portion and a second region connecting the downstream portion and the intermediate portion. The intermediate portion has a reduced cross-section provided with a predetermined angle ranging from 3° to 20°. [00041] The present subject matter also provides a method of manufacturing a cylinder head of an internal combustion engine having at least one exhaust port. The method includes the steps of forming an integrated sand core having a stepped diameter or cross-sectional area before at least a predetermined distance ranging between 6 mm to 12 mm from a downstream portion of the exhaust port. This step is followed by forming a locating element beyond the stepped diameter or cross-sectional area of the integrated sand core, and receiving the locating element of the integrated sand core by a metal core.
[00042] In an implementation, the forming process described above includes integral forming of the at least one exhaust port along with at least one intake port and a combustion chamber. Further, the method involves the step of low pressure die casting (LPDC).
[00043] In one implementation, the present subject matter provides a cylinder head in which the exhaust port is provided with a diameter or cross-sectional area that is substantially closer to the diameter or cross-sectional area of the exhaust pipe, but not perfectly matching to that of the diameter or cross-sectional area of the outlet portion of the exhaust port. In an embodiment, the present subject matter involves creating a stepped portion in the casting of the exhaust port. The modification is done at the exit point of the port for a width of approximately 6 -12 mm towards the end of the port. The length of the second region of the exhaust port that ranges approximately between 2.5 mm to 4 mm ensures that the minimum land required for mounting the exhaust pipe to the port is maintained after machining over and above any production variations that may arise. [00044] Moreover, the lack of consistency of the sheet metal flaring process is compensated by the casting process involving forming of integrated sand core for the exhaust port, which achieves the desired consistency, thereby reducing any variations in the process with a tolerance of + 0.2 mm of diameter or correspondingly to the cross-sectional area. Moreover, the casting process of the

cylinder head involving forming of sand core enables achieving required surface finish. Taking any manufacturing variations into consideration, the present subject matter achieves a ratio of diameter or cross-sectional area of the outlet of the portion of the port to that of the inlet of the exhaust pipe diameter or cross-sectional area ranging from 1:1 to 1:1.3, which helps in achieving the desired improvement in efficiency of catalytic converter without compromising on the engine performance.
[00045] In one embodiment, the cross-sectional area of the port at the valve seat, or the corresponding diameter of the port at the valve seat is close to 20 mm. Thus, the diameter of the port increases from the port near the valve seat till it reaches the port intermediate portion, after which, it reduces at the outlet portion of the exhaust port. This helps in achieving the desired restriction in outlet flow, . which increases the exhaust gas velocity. Further, in an implementation, increase in gas velocity is directly proportional to area of the outlet region of the exhaust port achieved as a result of reduction in diameter or cross-sectional area of the outlet portion of the exhaust port as a result of the reduced cross-section before the outlet portion of the exhaust port.
[00046] In continuation to what has been described in the preceding paragraph, in an implementation, a nozzle action caused due to the reduced cross-section provided towards the end of the exhaust port of the present subject matter, helps to increase the velocity of the exhaust gases. This phenomenon supports in quickly moving the exhaust gases to the CAT at a higher volumetric rate without resulting in drop in temperature of the exhaust gases. Thus, faster light-off of the CAT is achieved.
[00047] Further, the nozzle action caused due to the reduced cross-section provided towards the end of the exhaust port quickly transfers the exhaust gases from exhaust port to the exhaust pipe and through to the muffler towards the end of the exhaust pipe. This results in quick removal of the diluted gases in the combustion chamber for the next cycle of combustion. Thus, the volumetric efficiency is enhanced. This also helps in better breathing and improving low end

torque of the engine. This in turn, increases the performance of the engine at the desired operating points.
[00048] Moreover, the generally known exhaust systems are provided with secondary air injection (SAI) outlet at the exhaust ports to improve conversion of emission gases such as NOx, HC and CO. Thus, providing a SAI outlet at the reduced cross-section of the exhaust port helps in improving suction due to the vacuum created at the reduced cross-section. Further, this also ensures that more oxygen is made available at the catalytic converter disposed downstream of the exhaust pipe. This enables improving the catalytic converter's efficiency and the performance of the engine.
[00049] Arrows wherever provided in the top right corner in the drawings depicts direction with respect to the vehicle, wherein an arrow F denotes front direction, an arrow R indicates rear direction, an arrow UP denotes upward direction, an arrow DW denotes downward direction, an arrow RH denotes right side, and an arrow LH denotes left side.
[00050] Fig. 1 illustrates a two-wheeled vehicle (100), which is an exemplary motor vehicle, having an IC engine (101) that is vertically disposed. Preferably, the IC engine (101) is a single-cylinder type IC engine. The two-wheeled vehicle comprises a front wheel (110), a rear wheel (103), a frame member (102) shown schematically, a fuel tank (121) and seat (106). The frame member (102) includes a head pipe (111), a main tube (not shown), a down tube (not shown), and seat rails (not shown). The head pipe (111) supports a steering shaft (not shown) and two telescopic front suspension(s) (114) (only one shown) is attached to the steering shaft through a lower bracket (not shown). The two telescopic front suspension(s) (114) supports the front wheel (110). The upper portion of the front wheel (110) is covered by a front fender (115) mounted to the lower portion of the telescopic front suspension (114) at the end of the steering shaft. A handlebar (108) is fixed to upper bracket (not shown) and can rotate to both sides. A head light (109), a visor guard (not shown) and instrument cluster (not shown) is arranged on an upper portion of the head pipe (111). The down tube may be located in front of the IC engine (101) and extends slantingly downward from

head pipe (111). The main tube is located above the IC engine (101) and extends rearward from head pipe (111). The IC engine (101) is mounted at the front by the down tube and connects the rear of the IC engine (101) at the rear portion of the main tube.
[00051] A fuel tank (121) is mounted on the horizontal portion of the main tube (112). Seat rails are joined to main tube and extend rearward to support a seat (106). A rear swing arm (not shown) is connected to the.frame member (102) to swing vertically, and a rear wheel (103) is connected to rear end of the rear swing arm (118). Generally, the rear swing arm is supported by a mono rear suspension (117) (as illustrated in the present embodiment) or two suspensions on either side of the two-wheeled vehicle. A tail light unit (not shown) is disposed at the end of the two-wheeled vehicle at the rear of the seat (106). A grab rail (105) is also provided on the rear of the seat rails. The rear wheel (103) arranged below seat (106) rotates by the driving force of the IC engine (101) transmitted through a chain drive (116) from the IC engine (101). A rear fender (127) is disposed above the rear wheel (103).
[00052] Fig. 2 illustrates a right-side view of an internal combustion engine (101) including its exhaust system, in accordance with the embodiment as depicted in Fig. 1. In an embodiment, the internal combustion engine (101) includes a cylinder head assembly (210) having a cylinder head (203) and a cylinder head cover (202) mounted atop the cylinder head (203). In an embodiment, the internal combustion engine (101) is a single cylinder engine. More particularly, in one embodiment, the internal combustion engine (101) is a four-stroke internal combustion engine (101). In other alternative embodiment, the internal combustion engine (101) can include more than one cylinder head (203), or a plurality of cylinders. In an embodiment, the cylinder head (203) of the present subject matter includes one or more ports (not shown in this figure). For example, an exhaust port (not seen in this figure) of the internal combustion engine (101) enables exiting out the exhaust gases arising out of the combustion of the air-fuel mixture that occurs inside the combustion chamber (not shown) of the internal combustion engine (101). The gases exiting from the exhaust port are transported

through an exhaust pipe (200) of the exhaust system of the internal combustion engine (101). In an embodiment, the exhaust pipe (200) includes an inlet opening (201) which is connected to the exhaust port (not seen in this figure) of the internal combustion engine (101) for enabling smooth travel of the exiting exhaust gases.
[00053] In one embodiment, the cylinder head (203) of the internal combustion engine (101) is mounted atop a cylinder block (204), which together with crankcase (205) allows up and down movement of piston (not seen in this figure) of the internal combustion engine (101) for effecting optimal burning of the air-fuel mixture entering the combustion chamber. In an embodiment, the exhaust pipe (200) of the present subject matter includes a first bend (208) adjacent to the inlet opening (201) and a second bend (209) farther from the first bend (208). In an embodiment, the distance between the first bend (208) and the second bend (209) is defined by a vertical space available between the exhaust port and the ground clearance (C) shown in Fig 1 of the vehicle (100). In an embodiment, the engine (101) includes at least one spark plug. In an embodiment, the vehicle (100) is a saddle-ride type vehicle. The distance between the first bend (208) and the second bend (209) also depends, for example, on the diameter of the front wheel (not shown in this figure) and the rear wheel (not shown in this figure) and the wheel base between both the wheels.
[00054] In an embodiment, the exhaust pipe (200) includes at least one catalytic converter unit (206). Most particularly, the exhaust pipe (200) includes the at least one catalytic converter unit (206) substantially closer to the exhaust port of the cylinder head, in particular, the catalytic converter unit (206) is disposed between the first bend (208) and the second bend (209) of the exhaust pipe (200). In an embodiment, the at least one catalytic converter unit (206) is a pre-catalytic converter or an auxiliary catalytic converter, which is provided upstream of a main catalytic converter in the exhaust system of the present subject matter. In an alternative embodiment, the main catalytic converter (not shown) is disposed within the muffler assembly (130) of the exhaust system of the present subject matter. In an embodiment, closer the catalytic converter unit (206) to the exhaust

port, higher is the efficiency of-the catalytic converter unit (206). In an embodiment, the catalytic converter unit is disposed at a predetermined distance ranging approximately between 175 mm to 225 mm from a tapering section of said exhaust port (not seen in this figure).
[00055] In an embodiment, an oxygen sensor (207) is disposed substantially closer and upstream to the catalytic converter unit (206). For example, in one embodiment, the oxygen sensor (207) is disposed at a distance of about 15 mm to 20 mm upstream of the catalytic converter unit (206).
[00056] Fig. 3 (a) illustrates a cross-sectional front view of the cylinder head assembly (210) of the internal combustion engine (101), in accordance with an implementation of the present subject matter. In an embodiment, the cylinder head assembly (210) of the present subject matter has.at least one intake port (301) that allows entry of air-fuel mixture into the combustion chamber (not shown). In an embodiment, the intake port (301) is seated on an intake valve seat (302) at a juncture where an intake valve is disposed at an intake valve disposition opening (303) on the cylinder head assembly (210). In an embodiment, the cylinder head assembly (210) includes at least one exhaust port (304) disposed on the other side of the intake port (301). In an alternative embodiment, the cylinder head assembly (210) can include more than one exhaust port (304). In an embodiment, the exhaust port (304) is seated on an exhaust valve seat (305) of an exhaust valve (306). In an embodiment, the portion of the exhaust port (304) that is near the exhaust valve seat (305) is an upstream portion (310). In one embodiment, the diameter of the upstream portion (310) of the exhaust port (304) is approximately 20 mm. In an embodiment, an intermediate portion (308) of the exhaust port (304) divides the exhaust port (304) into two regions, viz., a first region (311) that is more than three-fourth of the entire exhaust port (304) extending between the upstream portion (310) and the intermediate portion (308), and a second region (312) that is substantially equal to or lesser than one-fourth of the entire exhaust port (304) extending between the intermediate portion (308) and a downstream portion (307) of the exhaust port (304). In an embodiment, the intermediate

portion (308) is disposed at approximately a distance of 6 mm to 12 mm from the downstream portion (307) of the exhaust port (304).
[00057] In an embodiment, the intermediate portion (308) of the exhaust port (304) includes a reduced cross-section (309). In one embodiment, the reduced cross-section (309) can include a tapering section. In an embodiment, the reduced cross-section (309) is provided with a predetermined angle of 3° to 20°, for example a tapering angle ranging from 3° to 20°. For instance, in an embodiment, . the reduced cross- section (309) has an upstream diameter or cross-sectional area substantially greater than a downstream diameter or cross-sectional area. In an embodiment, the length of the second region (312) of the exhaust port (304) ranges approximately between 2.5 mm to 4 mm, which ensures that the minimum land required for mounting the exhaust pipe (not seen in this Figure) to the port (304) is maintained. Further, in an alternative embodiment, the cylinder head assembly (210) includes two exhaust ports seated on two exhaust valve seats of two corresponding exhaust valves. In this embodiment, both the exhaust ports converge upstream of the reduced cross-section (309), which thereafter adjoins the exhaust pipe in a similar manner as that of the previous embodiment containing the single exhaust port (304).
[00058] Fig. 3 (b) illustrates a cross-sectional view of exhaust port (304) taken at the section Z-Z of the engine depicted in Fig. 3 (a), in accordance with one implementation of the present subject matter. Fig. 3 (c) illustrates a cross-sectional view of exhaust port (304) taken at the section XX-XX of the engine depicted in Fig. 3 (a), in accordance with one implementation of the present subject matter. Fig. 3 (d) illustrates a cross-sectional view of exhaust port (304) taken at the section YY-YY of the engine depicted in Fig. 3 (a), in accordance with one implementation of the present subject matter. In an embodiment, the diameter or cross-sectional area of the exhaust port at the section Z-Z, which is at the first region of the exhaust port (304), as depicted in Fig. 3 (b) is substantially lesser than the diameter or cross-sectional area of the exhaust port at the section XX-XX, which is at the intermediate portion (308) of the exhaust port (304) as depicted in Fig. 3 (c). Similarly, the diameter or cross-sectional area of the

exhaust port (304) at the section XX-XX, which is at the intermediate portion (308) of the exhaust port (304) is greater than the diameter or cross-sectional area of the exhaust port at the section YY-YY, which is taken at the second region (312) of the exhaust port (304) as depicted in Fig. 3 (d). As per another embodiment, the profile of the exhaust port may be any non-circular cross section e.g. like a D-shape shown in Fig 3(b) & similarly the shape of the exhaust port at intermediate portion (308) as well as the downstream portion (307) can be a non-circular cross section. In such embodiments, the equivalent cross sectional area of the exhaust port at upstream portion (310) is greater than the equivalent cross sectional area of the exhaust port (304) at the intermediate portion (308), and the cross-sectional area of the exhaust port (304) at the downstream portion (307) is lesser than the cross-sectional area of the intermediate portion (308). Such a specific configuration enables achieving higher velocity of exhaust gases, increased volumetric efficiency without compromising the flow rate of the exhaust gases.
[00059] Fig. 4 (a) illustrates a cross-sectional view of a first exemplary exhaust system (400a) of the internal combustion engine (101), in accordance with an embodiment of the present subject matter. In an embodiment, the first exemplary exhaust system (400a) includes a first cross-sectional area (Apr) of the downstream portion (307) of the exhaust port (304) substantially equal to a second cross-sectional area (APE) of the inlet opening (201) of the exhaust pipe (200). [00060] In an embodiment, the second cross-sectional area (APT) of the inlet opening (201) of the exhaust pipe (200) is approximately 1.10 to 1.20 times that of the first cross-sectional area (Apr) of the downstream portion (307) of the exhaust port (304), i.e., both the cross-sectional areas are substantially equal, but does not match. In an embodiment, the exhaust pipe (200) is attached to the exhaust port (304) by means of a mounting flange (401), which is comfortably mounted on to the mounting region of the downstream portion (307) of the exhaust port (304). Further, in an embodiment, the intermediate portion (308) of the exhaust port (304) includes a reduced cross-section (309). In one embodiment, the reduced cross-section (309) can include a tapering cross-section (309-1). In an

embodiment, the. tapering cross-section (309-1) is provided with a predetermined angle of 3° to 20°, for example a tapering angle ranging from 3° to 20°. [00061] Fig. 4 (b) illustrates a cross-sectional view of a second exemplary exhaust system (400b) of the internal combustion engine (101), in accordance with an embodiment of the present subject matter. In an embodiment, the second exemplary exhaust system (400b) includes a first cross-sectional area (APT) of the downstream portion (307) of the exhaust port (304) substantially equal to a second cross-sectional area (APE) of the inlet opening (201) of the exhaust pipe (200). Further, in an embodiment, the intermediate portion (308) of the exhaust port (304) includes a reduced cross-section (309). In one embodiment, the reduced cross-section (309) can include a smooth merging cross-section (309-2). In an embodiment, the smooth merging cross-section (309-2) is provided with a predetermined angle of 3° to 20°.
[00062] Fig. 4 (c) illustrates a cross-sectional view of a third exemplary exhaust system (400c) of the internal combustion engine (101), in accordance with an embodiment of the present subject matter. In an embodiment, the second exemplary exhaust system (400b) includes the first cross-sectional area (APT) of the downstream portion (307) of the exhaust port (304) substantially lesser than the second cross-sectional area (APE) of the inlet opening (201) of the exhaust pipe (200).
[00063] In an embodiment, the second cross-sectional area (APE) of the inlet opening (201) of the exhaust pipe (200) is approximately 1.2 to 1.5 times that of the first cross-sectional area (APT) of the downstream portion (307) of the exhaust port (304). In an embodiment, the exhaust pipe (200) is attached to the exhaust port (304) by means of the mounting flange (401), which is comfortably mounted on to the mounting region of the downstream portion (307) of the exhaust port (304). Further, in an embodiment, the intermediate portion (308) of the exhaust port (304) includes a reduced cross-section (309). In one embodiment, the reduced cross-section (309) can include a tapering cross-section (309-1). In an embodiment, the tapering cross-section (309-1) is provided with a predetermined angle of 3° to 20°, for example a tapering angle ranging from 3° to 20°.

[00064] Fig. 4 (d) illustrates a cross-sectional view of a fourth exemplary exhaust system (400d) of the internal combustion engine (101), in accordance with an embodiment of the present subject matter. In an embodiment, the fourth exemplary exhaust system (400d) includes a first cross-sectional area (APT) of the downstream portion (307) of the exhaust port (304) substantially lesser than the second cross-sectional area (APE) of the inlet opening (201) of the exhaust pipe (200). Further, in an embodiment, the intermediate portion (308) of the exhaust port (304) includes a reduced cross-section (309). In one embodiment, the reduced cross-section (309) can include a smooth merging cross-section (309-2). In an embodiment, the smooth merging cross-section (309-2) is provided with a predetermined angle of 3° to 20°.
[00065] Fig. 5 illustrates a third exemplary exhaust system (500) depicting a cross-sectional view of the exhaust port (304) of the internal combustion engine, in accordance with another embodiment of the present subject matter. In an embodiment, the intermediate portion (308), more particularly, the reduced cross-section (309) of the exhaust port (304) is provided with an entry point (502) for receiving at least one secondary air injection outlet conduit (501). In an implementation, providing the secondary air injection outlet conduit (501) at the reduced cross- section (309) of the exhaust port (304) helps in improving suction due to the vacuum created at the reduced cross-section (309). Further, this also ensures that more oxygen is made available at the catalytic converter (not shown in this figure) disposed downstream of the exhaust pipe (200). This enables improving the catalytic converter's efficiency and the performance of the engine at desired operating points.
[00066] Fig. 6 (a) depicts a first characteristic curve (600) of exhaust gas temperature in the exhaust system of the internal combustion engine, in accordance with an embodiment of the present subject matter. In an exemplary embodiment, the first characteristic curve (600) depicts two varying curves, viz., a first temperature curve (601) for an engine with conventional cylinder head, and a second temperature curve (602) for an engine with improved cylinder head as described in the present subject matter. In an embodiment, the temperature of

exhaust gases travelling through- the exhaust port (304) and into the exhaust pipe (200) has a steeper drop in the case of the first temperature curve (601) that has a conventional cylinder head assembly in comparison with the second temperature curve (602) employing the improved cylinder head assembly as described in the present subject matter. The reason for this steeper drop in the exhaust gases temperature is the improved structure of the exhaust port (304) at its outlet where it is joined with the exhaust pipe (200). In case of the conventional cylinder head, the exhaust port gradually increases in its diameter or cross-sectional area from the valve seat till the downstream portion of the exhaust port (304). On, the contrary, the exhaust port (304) of the cylinder head assembly (210) of the present subject matter involves an initial increase in cross-sectional area and a reduction in cross-sectional area towards the end of the exhaust port (304), as can be observed from Fig. 3 (a), 3 (b), 3 (c) arid 3 (d). Further, the conventional exhaust systems also include the inlet opening of the exhaust pipe (200) having a diameter or cross-sectional area that is lesser than the diameter or cross-sectional area of the exhaust port (304) at its downstream portion (307). In such a case, the velocity of the exhaust gases exiting out of the exhaust port (304) does not show a significant increase as they progress within the exhaust pipe passage. For instance, in case of the conventional cylinder head, at a distance of approximately 200 mm from the exhaust port, where the catalytic converter is intended to be located, the temperature of the exhaust gases drops close to 12 - 14% than in the case of the improved cylinder head of the present subject matter. Such a steep drop in the exhaust gases temperature is due to the loss of velocity in the exhaust gas stream. The impact of the conventional exhaust systems on the output exhaust gas velocity is further described with reference to Fig. 6 (b) and Fig. 6 (c) provided below.
[00067] Fig. 6 (b) illustrates a cross-sectional view of a conventional exhaust system (600 (b)) depicting the intersection of the exhaust port and the exhaust pipe. While, Fig. 6 (c) illustrates a cross-sectional view of an exemplary exhaust system (600 (c)) depicting the intersection of the exhaust port and the exhaust pipe, in accordance with an embodiment of the present subject matter. As can be

observed from the conventional exhaust system (600 (b)), the cross-sectional area of the conventional exhaust pipe (200') abruptly decreases at the joining face of the exhaust port (304'). Such an abrupt change (603') in the cross-sectional area tends to create turbulence in the exhaust gas flow. On the "contrary, the exhaust system (600 (c)) of the present subject matter as seen in Fig. 6 (c), provides a reduction in cross-sectional area within the exhaust port (304), which not only helps in increasing the exhaust gas velocity from that point onwards, but also ensures that there exists a smoother transition of exhaust gas flow, thereby preventing any turbulence in the exhaust gas flow caused due to such reduction in cross-sectional area towards the downstream portion (307) of the exhaust port (304).
[00068] Moreover, the reduction in cross-sectional area towards the downstream portion (307) of the exhaust port (304) of the exhaust system (600(c)) of the present subject matter, ensures that the high pressure within the exhaust port (304) is fully utilized for achieving effective increase in exhaust gas velocity without any losses. On the contrary, any increase in velocity of the exhaust gases that can be observed in the conventional exhaust system (600 (b)), will experience drop in pressure at the exhaust pipe (200'), which will impact the effective increase in the exhaust gas velocity.
[00069] On the other hand, the improved cylinder head of the present subject matter is provided with a reduced cross-section when the exhaust gases exiting out of the combustion chamber approaches the downstream portion of the exhaust port (304). The reduced cross-section, and in particular, the tapered angle provided ensures that the velocity of the exhaust gases flowing past the reduced cross-section increases. Moreover, in case of the exemplary exhaust systems of the present subject matter, the diameter or cross-sectional area of the inlet opening of the exhaust pipe (200) varies between 1.10 to 1.20 times that of the diameter or cross-sectional area of the downstream portion of the exhaust port (304), such a configuration of the exhaust port and the exhaust pipe joining face in combination with the reduced cross-section and the angle of the reduced cross-section ensures that the velocity of the exhaust gases in the exhaust pipe passage does not drop

significantly. For instance, at a distance of approximately 175 mm to 220 mm from the reduced cross-section of the exhaust port (304), the catalytic converter unit (206) is disposed in the exhaust pipe (200). The velocity of the exhaust gases reaching the catalytic converter unit (206) of the present subject matter is high enough so that the temperature of the exhaust gases is at least 12 - 14% higher than in the case of the conventional cylinder head, thereby enabling an early light-off of the catalytic converter unit (206), which in turn increases the efficiency of the catalytic converter unit (206).
[00070] Fig. 7 depicts a second characteristic curve (700) of engine torque of the internal combustion engine, in accordance with an embodiment of the present subject matter. In an embodiment, the second characteristic curve (700) depicts a first torque curve (701) for engine with conventional cylinder head and a second torque curve (702) for engine with improved cylinder head as described in the present subject matter. In an embodiment, the first torque curve (701) has a significantly low torque (Nm) at low engine speed (rpm) as compared to the second torque curve (702). Such a significant increase in engine torque at low engine speed in the improved cylinder head of the present subject matter is achieved as a result of the specific profile design of the exhaust port (304), for example, a reduced cross-section (309). The increase in the velocity of the exhaust gases at the reduced cross-section of the exhaust port (304) ensures that there is an improvement in the low-end torque of the engine and-it also enhances the performance of the engine at certain specific operating points. [00071] In an implementation, the nozzle action caused due to the tapered profile section towards the end of the exhaust port (304) creates a back pressure or restriction during the valve overlap period. This back pressure facilitates the exhaust gases to push the piston down effectively and helps in improving low end torque of the engine. Further, the above low end torque is achieved without compromising mid-range and high end torque. In high speed region of the engine, the nozzle action caused due to the tapered profile section of the exhaust port (304) assists in sending the exhaust gases quickly to the muffler body (130) without any restriction for next cycle and thereby enhancing power of the engine.

[00072] Fig. 8 depicts an exemplary method (800) of manufacturing of the . cylinder head in accordance with an embodiment of the present subject matter. In an exemplary embodiment, the method (800) of manufacturing the cylinder head • of the present subject matter involves a first step (805) of forming an integrated sand core. The step (805) of forming the integrated sand core involves creating a sand core that is integral to the cylinder head along with the one or more intake ports and the one or more exhaust ports. In one embodiment, the sand core of the improved exhaust port of the present subject matter is formed integrally with that of the cylinder head. At a second step (810), the method (800) involves providing a stepped diameter or cross-sectional area before the outlet or the downstream portion of the exhaust port (304). The stepped diameter or cross-sectional area provided towards the end of the exhaust port (304) enables forming of the tapered profile portion of the exhaust port (304) with the desired characteristics of increasing the velocity of the exhaust gases without causing a performance drop in terms of drop in low end torque of the engine. At a third step (815), the method (800) involves forming a locating element for the integrated sand core beyond the stepped diameter or cross-sectional area. The locating element thus formed ensures that the sand core is held stably during the casting process and metal is filled in the throat of the exhaust port after the stepped diameter or cross-sectional area.
[00073] At a fourth step (820), the method (800) involves receiving the locating element that is formed in the sand core beyond the stepped diameter or cross-, sectional area of the exhaust port (304) by a metal core, which is held towards the ends of the sand core. At a fifth step (825), the method (800) involves flow of material, for example, in an exemplary embodiment the material is an aluminum alloy. The aluminum alloy is allowed to flow into the cast containing the sand core. At a sixth step (830), the method (800) involves low pressure die casting (LPDC) of the aluminum alloy in the cast. Further, at a seventh step (835), the method (800) involves removal of gates or air vents from the cast after the low pressure die casting is carried out for a predetermined time and at predetermined operating conditions. Furthermore, at an eighth step (840), the method (800)

involves cleaning of the casted part; the cleaning involves operations such as fettling for removal of undesired edges and burrs from the casted part. At a ninth step (845), the method (800) involves heat treatment of the die cast part for a predetermined time and at predetermined operating conditions. Further, at a tenth step (850), the method (800) involves machining o'f the cast cylinder head. The machining is done to ensure that the desired ratio of tapered angle to the length of the exhaust port (304) at the second region connecting the intermediate portion and the downstream portion is achieved. It is important to achieve the above described desired ratio, as it is critical to achieve the desired increase in velocity of the exhaust gases without compromising the performance characteristics such as low end torque and power.
[00074] Fig. 9 illustrates a, cross-sectional view of the cylinder head assembly of the present subject'matter depicting an intake port passage and an exhaust port passage with an integrated sand core disposed therein. In an embodiment, the cylinder head assembly (210) of the present subject matter is die casted with the help of the integrated sand core formed therein. In an embodiment, an intake port metal core (901) is provided to hold the underneath sand core firmly during die-casting process described above. In one embodiment, an intake port sand core (903), an exhaust port sand core (904) along with a combustion chamber sand core (905). In one embodiment, the sand cores (903, 904, 905) of the intake port, the exhaust port and the combustion chamber are glued to form the integrated sand core. In an embodiment, the exhaust port sand core (904) is provided with a stepped diameter or cross-sectional area (906) before the outlet portion of the exhaust port (304). In one implementation, a locating element (907) is formed beyond the stepped diameter or cross-sectional area (906) of the exhaust port (304),' which ensures that the necessary reduced cross-section before the downstream portion of the exhaust port (304) is formed in the die-cast cylinder head assembly (210) for effecting the increase in exhaust gas velocity and improving low-end torque without compromising on engine performance. In one embodiment, the locating element (907) is formed on an exhaust core metal core (902).

[00075] Many modifications and variations of the present subject matter are possible within the spirit and scope of the present subject matter, in the light of " above disclosure.

List of reference signs:
100 vehicle 305 exhaust valve seat
101 internal combustion engine 306 exhaust valve
102 frame member 307 downstream portion of
103 rear wheel 35 exhaust port

105 grab rail 308 intermediate portion
106 seat 309 reduced cross-section
108 handlebar 309-1 tapered cross-section
109 headlight 309-2 smooth merging cross-
i 110 front wheel 40 section f
111 head pipe 310 upstream portion of exhaust
114 front suspension port
115 front fender 311 first region of exhaust port
117 rear suspension 312 second region of exhaust
121 fuel tank 45 port
'130" muffleTbody" ' "400(a)"firs""exemplary"" "tfxHaifsT'
200 exhaust pipe system
201 inlet opening of exhaust pipe . 400(b) second exemplary exhaust
202 cylinder head cover system
203 cylinder head 50 401 mounting flange
204 cylinder block AEPT First cross-sectional
205 crankcase area of exhaust port
206 catalytic converter unit APE Second . cross-
207 oxygen sensor sectional area of exhaust pipe
208 first bend of exhaust pipe 55 500 Third exemplary exhaust
209 second bend of exhaust pipe system
210 cylinder head assembly, 501 .Secondary air injection

301 intake port (SAI) outlet conduit
302 intake valve seat 502 Entry point for SAI outlet
303 intake valve 60 600 First characteristic curve
304 exhaust port

601 First temperature curve for 820 Fifth step of exemplary
engine with conventional cylinder . 25 method
head 825 Sixth step of exemplary
602 Second temperature curve method
for engine with improved cylinder 830 Seventh step of exemplary
head method
603 Abrupt change in cross- 30 835 Eighth step of exemplary
section method
700 Second characteristic curve ■ 840 Ninth step of -exemplary
701 First torque curve for engine method
with conventional cylinder head 845 Tenth step of exemplary
702 Second torque curve for 35 method
engine with improved cylinder head 850 Eleventh step of exemplary
800 Exemplary method of method
manufacturing cylinder head 901 . Intake port metal core
805 First step of exemplary 902 Exhaust port metal core
method 40 903 Intake port sand core
810 Second step of exemplary 904 Exhaust port sand core
method 905 Combustion chamber sand
814 Third step of exemplary core
method 906 Stepped diameter or cross-
8.15 Fourth step of exemplary 45 sectional area .
method 907 Locating element

We claim:
1. An internal combustion engine (101) for a vehicle (100), said internal
combustion engine (101) comprising:
at least one cylinder head (203) of a cylinder head assembly (210), said at least one cylinder head (203) includes at least one intake port (301);
at least one spark plug;
the at least one intake port (301) is seated on an intake valve seat (302) at a juncture where an intake valve is disposed at an intake valve disposition opening (303) on said cylinder head assembly (210);
at least one exhaust valve (306);
a combustion chamber for receiving intake charge from a fuel supply device through at least one intake port (301); and
at least one exhaust port (304) seated on an exhaust valve seat (305) of said exhaust valve (306), said at least one exhaust port (304) capable of expelling combusted gases from said combustion chamber to atmosphere through an exhaust pipe (200) of said vehicle (100), said at least one exhaust port (304) having an upstream portion (310) adjoining said combustion chamber and a downstream portion (307) adjoining an inlet opening (201) of said exhaust pipe (200), said downstream portion (307) of said exhaust port (304) having a first cross-sectional area (APT) substantially equal to a second cross-sectional area (APE) of said inlet opening (201) of said exhaust pipe (200).
2. The internal combustion engine (101) as claimed in claim 1, wherein said exhaust port (304) has an intermediate.portion (308) disposed adjacent to said downstream portion (307).
3. The internal combustion engine (101) as claimed in claim 2, wherein said exhaust port (304) has a first region (311) connecting an upstream portion (310) of said exhaust port (304) and said intermediate portion (308) and a second region (312) connecting said downstream portion (307) and said intermediate portion (308)..
4. The internal combustion engine (101) as claimed in claim 3, wherein said intermediate portion (308) has a reduced cross-section (309) provided with a predetermined angle.
5. The internal combustion engine (101) as claimed in claim 4, wherein said predetermined angle ranges from 3° to 20°.

6. The internal combustion engine (101) as claimed in claim 4, wherein said reduced cross-section (309) includes a tapered cross-section (309-1) having an upstream cross-sectional area substantially greater than a downstream cross-sectional area.
7. The internal combustion engine (101) as claimed in claim 4, wherein said reduced cross-section (309) includes a smooth merging cross-section (309-2) having an upstream cross-sectional area substantially greater than a downstream cross-sectional area.
8. The internal combustion engine (101) as claimed in claim 3, wherein said second region (312) of said exhaust port (304) has length ranging approximately, between 2.5 mm to 4 mm.
9. The internal combustion engine (101) as claimed in claim 1, wherein said first cross-sectional area (APT) ranges approximately between 175 mm2 to 490mm2(equivalent of 15 mm to 25 mm of diameter).

10. The internal combustion engine (101) as claimed in claim 1,- wherein said exhaust pipe (200) includes at least one catalytic converter unit (206) disposed at a predetermined distance from said exhaust port (304).
11. The internal combustion engine (101) as claimed in claim 10, wherein said exhaust pipe (200) includes an oxygen sensor (207) disposed between said exhaust port (304) and said catalytic converter unit (206), said oxygen sensor (207) disposed substantially closer to said catalytic converter unit (206).
12. The internal combustion engine (101) as claimed in claim 10, wherein said at least one catalytic converter unit (206) is disposed at a predetermined distance ranging approximately between 175 mm to 300 mm from a reduced cross-section (309) of said exhaust port (304).
13. The internal combustion engine (101) as claimed in claim 10, wherein said oxygen sensor (207) is disposed at a predetermined distance ranging approximately between 15 mm to 20 mm upstream of said at least one catalytic converter unit (206).
14. The internal combustion engine (101) as claimed in claim 2, wherein said intermediate portion (308) of said exhaust port (304) receives at least one secondary air injection outlet conduit (501).

15. A method (800) of manufacturing, a cylinder head (203) of an internal
combustion engine (lOl)having at least one exhaust port (304), said method (800)
comprising:
forming (805) an integrated sand core (903, 904) having a stepped cross-sectional area before at least a predetermined distance from a downstream portion (307) of said exhaust port (304);
forming (815) a locating element (907) beyond said stepped cross-sectional area (906) of said integrated sand core (903, 904); and
receiving (820) said locating element (907) of said integrated sand core (903, 904) by a metal core (901, 902).
16. The method (800) as claimed in claim 15, wherein said forming (805) said integrated sand core (903, 904) includes integrally forming said at, least one exhaust port (304) along with at least one intake port (301) and a combustion chamber.
17. The method as claimed in claim 16, wherein said method (800) comprises low pressure die casting (LPDC).
18. The method as claimed in claim 15, wherein said forming (805) an integrated sand core (903, 904) comprises forming (810) a stepped cross-sectional area before at least said predetermined distance ranging between 6 mm to 12 mm from said downstream portion of said exhaust port (304).
19. An internal combustion engine (101) for a vehicle (100), said internal .
combustion engine (101) comprising:
at least one cylinder head (203) of a cylinder head assembly (210), said at least one cylinder head (203) includes at least one intake port (301);
at least one spark plug;
the at least one intake port (301) is seated on an intake valve seat (302) at a juncture where an intake valve is disposed at an intake valve disposition opening (303) on said cylinder head assembly (210);
at least one exhaust valve (306);
a combustion chamber for receiving intake charge from a fuel supply device through at least one intake port (301); and

at least one exhaust port (304) seated on an exhaust, valve seat (305) of said exhaust valve (305), said at least one exhaust port (304) capable of expelling combusted gases from said combustion' chamber to atmosphere through an exhaust pipe (200) of said vehicle (100), said at least one exhaust port (304) having an upstream portion (310) adjoining said combustion chamber and a downstream portion (307) adjoining an inlet opening (201) of said exhaust pipe (200), said downstream portion (307) of said exhaust port (304) having a first cross-sectional area (APT) substantially lesser than a second cross-sectional area (APE) of said inlet opening (201) of said exhaust pipe (200).
20. The internal combustion engine (101) as claimed in claim 19, wherein said second cross-sectional area (APE) of said inlet opening (201) of said exhaust pipe (200) is approximately 1.2 to 1.5 times said first cross-sectional area (APT) of said downstream portion (307) of said exhaust port (304).
21. The internal combustion engine (101) as claimed in claim 1, wherein said second cross-sectional area (APE) of said inlet opening (201) of said exhaust pipe (200) is approximately 1.10 to 1.20 times said first cross-sectional area (APT) of said downstream portion (307) of said exhaust port (304). '
22. An internal combustion engine (101) for a vehicle (100), said internal
combustion engine (101) comprising:
at least one cylinder head (203) of a cylinder head assembly (210), said at least one cylinder head (203) includes at least one intake port (301);
at least one spark plug;
the at least one intake port (301) is seated in an intake valve seat (302) at a juncture where an intake valve is disposed at an intake valve disposition opening (303) on said cylinder head assembly (210);
at least one exhaust valve (306);
a combustion chamber for receiving intake charge from a fuel supply device through at least one intake port (301);
at least one exhaust port (304) seated on an exhaust valve seat (305) of said exhaust valve (306), said at least one exhaust port (304) capable of expelling combusted gases from said combustion chamber to atmosphere through an exhaust pipe (200) of said vehicle (100), said at least one exhaust port (304) . having an upstream portion (310) adjoining said combustion chamber and a downstream portion (307) adjoining an inlet opening (201) of said exhaust pipe

(200), said downstream portion (307) of said exhaust port (304) having a first cross-sectional area (APT) substantially lesser than a second cross-sectional area (APE) of said inlet opening (201) of said exhaust pipe (200);
said exhaust port (304) having an intermediate portion (308) disposed adjacent to said downstream portion (307);
said exhaust port (304) having a first region (311) connecting said upstream portion (310) of said exhaust port (304) and said intermediate portion (308) and a second region (312) connecting said downstream portion (307) and said intermediate portion (308); and
said intermediate portion (308) having a reduced cross-section (309) provided with a predetermined angle.
23. The internal combustion engine (101) as claimed in claim 22, wherein said first cross-sectional area (APT) ranges approximately between 15 mm to 25 mm.
24. The internal combustion engine (101) as claimed in claim 22, wherein said predetermined angle ranges from 3° to 20°.