Exhaust system for personal watercraft

An exhaust system for a personal watercraft provides an exhaust adapter plate and an exhaust header pipe that allows exhaust to exit from the rear of a horizontally mounted internal combustion engine. The exhaust adapter plate is mounted to the rear of the engine block. The exhaust adapter plate has openings corresponding to the engine exhaust port and engine cooling water jacket. The adapter plate also has an opening for the engine crankshaft. The exhaust header pipe is mounted to the engine with the adapter plate disposed therebetween. An exhaust passage through the exhaust header pipe passes transversely across the engine compartment within the watercraft. As the exhaust header pipe passes transversely across the engine compartment, the exhaust passage angles upwardly from the exhaust adapter plate to a high point, and angles downwardly from the high point to an exhaust outlet leading to a muffler. The exhaust passage through the exhaust header pipe is tuned, yet the configuration of the exhaust header pipe provides a compact design that is easily packaged within the engine compartment for a personal watercraft, and also provides for sufficient space rearward of the exhaust header pipe so that the exhaust system and the remainder of the engine can be easily serviced. Also, since the exhaust header pipe and the exhaust adapter plate are physically separate components, each can be designed to be manufactured using simpler manufacturing techniques.