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PT Boats of WWII
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PT Boats - General
Post a reply to: ELCO 80' mufflers
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[StartQuote] Hey Bob, Great question and interesting responses as well. Although the PT658 is a Higgins boat, they did use the same Packard engines as the Elco 80's. One detail that was mentioned I wanted to point out is untrue and is a common misconception. There was NEVER any seawater injected into the Exhaust pipes on Packard V12 Gas engines. The exhaust gas was purposely kept separated from the seawater by means of a "pipe within a pipe" arrangement. I am also fairly confident that these exhaust stacks as they were called, were made from copper and not stainless steel. This can easily be verified in the Elco Parts manual. The seawater leaving the Exhaust manifold connects to the Exhaust Stack outer piping (cooling jacket) and cools the stack from melting. At the other end of the stack, where it attaches to the transom via a "through hull" fitting, the sea water connects to the various muffler designs as defined in previous posts. The misconception occurs because although seawater is commonly injected directly into the stack on numerous Diesel Engine powered boats, where it causes no problems, this isnt the case on V12 Packards.. This is because when you have a 100 octane gasoline powered engine like on a PT Boat, the exhaust temps coming out of the Exhaust manifold can reach temps in excess of 900F. (I know this from personal experience!) If you injected seawater into the inner exhaust pipe of that stack it would instantly flash to steam and cause excessive back pressure in the exhaust system, reducing engine power, possible vapor lock and liquid backflow into the pistons of the engine while cooling off after shutdown. Engine operating procedures for both Elco and Higgins boats that I have read take great precautions in ensuring the Exhaust stack outer cooling jackets are full of water before startup, and promptly drained after shutdown in order to prevent damage to the stacks or the engine exactly for this reason. If one melted it would allow the seawater to mix into the exhaust with disasterous results! As far as the mufflers are concerned, what is said above seems correct from my sources as well. I hope this is helpful! Jerry Gilmartin PT658 Crewman Portland OR[EndQuote]
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