Snowmobile exhaust system

1. A snowmobile comprising:

a frame including a tunnel and an engine cradle forward of the tunnel;

a four-stroke engine mounted in the engine cradle, the engine having exhaust ports;

a drive track disposed below and operatively connected to the tunnel, the drive track being operatively connected to the engine for propulsion of the snowmobile;

left and right skis connected to the frame;

a left suspension assembly connecting the left ski to the frame;

a right suspension assembly connecting the right ski to the frame;

a straddle seat disposed on the tunnel above the drive track and rearwardly of the engine;

a pair of footrests supported by the frame;

a steering column operatively connected to the left and right skis;

a handlebar connected to the steering column; and

an exhaust system connected to the engine, the exhaust system including:

an exhaust manifold fluidly communicating with the exhaust ports of the engine, the exhaust manifold having an outlet;

a pre-muffler fluidly communicating with the outlet of the exhaust manifold and extending forwardly from the exhaust manifold;

springs connecting the pre-muffler to the exhaust manifold;

a generally U-shaped exhaust pipe extending forwardly from the pre-muffler to a first point disposed forwardly of the engine cradle and of the suspension assemblies, and extending rearwardly from the first point to a second point disposed rearwardly of a front of the engine cradle, the exhaust pipe having a substantially constant diameter, the pre-muffler fluidly communicating the outlet of the exhaust manifold with the exhaust pipe, and a maximum diameter of the pre-muffler being greater than the substantially constant diameter of the exhaust pipe; and

a muffler fluidly communicating the exhaust pipe with the atmosphere, at least a portion of the muffler being disposed rearwardly of the front of the engine cradle and to one lateral side of the engine, the muffler and the outlet of the exhaust manifold are disposed on opposite sides of a longitudinal centerline of the frame;

wherein the exhaust pipe has first, second, third, fourth, fifth, and sixth portions;

wherein the first portion extends forwardly from the pre-muffler and towards a longitudinal centerline of the frame;

wherein the second portion extends forwardly from the first portion and away from the longitudinal centerline;

wherein the third portion extends forwardly from the second portion and towards the longitudinal centerline;

wherein the fourth portion extends rearwardly from the third portion and away from the longitudinal centerline;

wherein the fifth portion extends rearwardly from the fourth portion and towards the longitudinal centerline;

wherein the sixth portion extends rearwardly from the fifth portion and away from the longitudinal centerline, a rear portion of the sixth portion extends inside the muffler;

wherein the first, second, and third portions are disposed on a first side of the longitudinal centerline and the fourth, fifth, and sixth portions are disposed on a second side of the longitudinal centerline; and

wherein a connection between the first and second portions and a connection between the fifth and sixth portions are disposed laterally inwardly of lateral sides of the engine.

2. The snowmobile of claim 1 , wherein the second point is disposed rearwardly of the left and right suspensions.

3. The snowmobile of claim 2 , wherein an outlet of the exhaust pipe is disposed forwardly of the footrests.

4. The snowmobile of claim 1 , wherein a connection between the first and second portions is disposed forwardly of a connection between the fifth and sixth portions.

5. The snowmobile of claim 1 , wherein the exhaust pipe is asymmetric about the longitudinal centerline.

6. The snowmobile of claim 1 , wherein the exhaust ports of the engine face towards a front of the snowmobile.

7. The snowmobile of claim 6 , wherein the outlet of the exhaust manifold is a single outlet.

8. The snowmobile of claim 1 , wherein a length of the pre-muffler is less than a length of the exhaust pipe.

9. The snowmobile of claim 1 , wherein the muffler is disposed forwardly of one of the footrests.

10. The snowmobile of claim 1 ,

wherein a length of the rear portion of the sixth portion of the exhaust pipe extending inside the muffler is less than 20 percent of a length of the exhaust pipe.

11. The snowmobile of claim 1 , wherein each of the left and right suspension assemblies includes at least one A-arm; and

wherein the first point is disposed forwardly of a portion of the A-arms.

12. The snowmobile of claim 11 , wherein each A-arm defines a steering axis about which a corresponding one of the left and right skis pivots; and

wherein the first point is disposed forwardly of the steering axes.

13. The snowmobile of claim 1 , further comprising:

a cowling connected to a forward portion of the frame and at least partially disposed around the exhaust pipe; and

a heat shield disposed between the cowling and a portion of the exhaust pipe.

14. The snowmobile of claim 1 , wherein the exhaust pipe is at least 1200 mm long.

15. The snowmobile of claim 14 , wherein a diameter of the exhaust pipe is less than 70 mm.

16. The snowmobile of claim 14 , wherein the exhaust pipe reduces engine noise by at least 6 decibels.