The top wall of a snowmobile tunnel, which accommodates the endless drive track of the snowmobile, is provided with recesses at locations corresponding to the path followed by studs carried by the endless track. The rear of the tunnel is connected to a molded rear member having a pattern of recesses matching that of the top wall of the tunnel. In yet another aspect of the invention, a heat exchanger for cooling engine coolant may be provided at the rear of the tunnel. The heat exchanger may be mounted to and partially spaced from the molded rear member. The heat exchanger may bear rearwardly extending ridges with upwardly extending lip at the far end. In some embodiments, a channel is provided on the upper end of the heat exchanger to promote air and snow flow over the rearwardly extending ridges.