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Turbocharging a Marine Engine
"J K" wrote in message . 201... good for efficiency and engine life. From what I've read in automotive repair histories, the turbocharged engines require more maintenance. J K Turbo-charging allows an engine to pack in move air and fuel, making the engine develop the same power as a much higher displacement naturally aspirated engine.The energy normally wasted in the exhaust is use to pump the incoming charge above normal atmosphere pressure. If you have more air, you can burn more fuel. The nice thing about a turbo as compared to a blower is that the amount of boost is related to the exhaust temperature, and this is related to the amount of fuel you are burning. In practical terms, it runs when you need it. The bottom line is that you can make a 300 cubic inch engine deliver the same power as a 450 cubic inch engine under full throttle, and run as efficiently as the 300 cubic inch engine when running at lower power settings. In automotive applications, the throttle lag means that the engine may take a little longer to come to full power, and you have to use a "waste gate" to prevent the turbo from stalling when you close the throttle quickly - like in a gear shift. In most boating application these performance issues are simply not an issue. Properly maintained and used, a turbo is a very long life item. There is one moving part - a single shaft with turbine and compressor fans. A turbo spins a very high speeds - 60 to 80 thousand RPM is not uncommon. The bearings are simple oil film in most cases. The oil provides both lubrication and cooling. The cooling thing can be very important because the turbine is driven by the exhaust. These bearings are the failure mechanism in automotive application. These bearings have to get oil when the engine starts up. In some engines the pressure builds rather slowly on startup. If the engine is revved before the turbo is properly lubricated, a bearing failure is in the cards. Another popular source of failure is during shutdown. Frequently, the driver will roar up to a stop and shut the engine off without letting the turbo bleed off the heat in the cooling oil. The heat soaks through the housing; the oil left in the turbo breaks down and cokes up the bearings. Sooner or later the one moving part of the turbo quits moving because the bearings are gummed up. Another common problem with turbos - if you build a big fire in a little furnace, the little furnace burns up. An engine has to be build to withstand the power developed during boost. A little known fact is that the old Dodge slant six was originally built as a race engine. Richard Petty wanted and engine built for turbo charging. If you look at one of these, you will notice that the intake and exhaust all come together with a turbo would be mounted. The other salient features was a very long stroke to extract all the power generated, and *very* heavy main bearings. When there were using in a naturally aspirated engine, they were not working very hard. The racing rules of the day required that a certain number of the engines had to be in productions automobiles to be allowed on the racetrack. The American public got a great deal out of this - these engines have a well deserved reputation as being unbreakable - they would keep running when they sounded like a shaken fruit jar full of marbles. These engines are still being run in industrial application like Lull lifts. The only reason they are not used in automobiles today is that the design could not be tamed to burn fuel without polluting. Rats. Mark Browne |
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