SEAL 6V9177 - Caterpillar

Water Cooled Exhaust
There are two basic types of exhaust systems used. The two systems are "wet" (water cooled) and dry exhaust systems. The main consideration is to design the system to remove the exhaust gases from the engine room and limit the backpressure to a minimum.The limits for a given engines' exhaust backpressure can be located in the TMI system. In general terms the backpressure limit is 27 inches of water for all Caterpillar turbocharged/turbocharged aftercooled engines. 34 inches of water is the limit for naturally aspirated engines. The 3600 series of engines have a limit of 10 inches of water. Some special rating, such as the 435 Hp 3208 E rating have a limit of 40 inches of water. You need to determine the limit of your engine, rating and then size the exhaust system to be below the limit. Remember that the closer you get to the limit the more affect the exhaust backpressure will have on the performance of the engine.Many "wet" exhaust systems utilize an exhaust riser to help prevent sea water from entering the engine through the exhaust system when the engine is not operating or when the boat is "backed down" quickly. As a general rule of thumb the riser should be at least 22 inches above the level of the sea water to the lowest portion of the riser.The minimum water flow requirements to a wet exhaust system can be calculated by using the following formula.Flow = Gallons per minute (L/min)Vd = Engine displacement [cubic inches (liters)]Ne = Rated speed (rpm)66,000 = constant for gallons285.785 = constant for litersA water lift muffler is also common in some of the smaller pleasure craft. If a water lift muffler is to be used the following are some points to pay close attention to.1. Size the muffler outlet for a minimum exhaust velocity (gas only) of 5000 ft/min at rated engine power and speed. The following formula will give the maximum pipe diameter, "De" that can be used to insure the 5000 ft/min velocity. De = The maximum water lift exhaust outlet pipe diameter [inches (mm)]Qe = Exhaust flow rate from the muffler [cfm (m3/min)]2. The tank itself should be of sufficient size. A rule of thumb would be at least 8 cubic inches per rated horsepower.3. The inlet pipe to the tank should be truncated near the top of the tank.4. The outlet pipe should extend to near the bottom of the tank (about 1 inch from the bottom) and should be angle cut (mitered) to increase exit gas velocity at lower loads and flow rates.5. A siphon break should be installed between the exhaust elbow and the high point of the outlet pipe from the muffler.Dry Exhaust
The dry exhaust system has some typical points that need to be considered as well.1. A flexible connection at the engine exhaust outlet. No more than 60 pounds of exhaust piping weight should be supported on the flexible connection.2. Flexible connection(s) are installed on the horizontal