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Old 08-07-2010, 16:56   #1
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Volvo Penta MD 7A Air Intake / Silencer Length

The sound of the ol' engine is a bit loud and rather than forking out on and installing special sound proofing panels around the engine., i was thinking of maybe extending or relocating the air intake/silencer and have it sucking air from outside. At present it sucks air from the engine compartiment which is located half under the companion way and cockpit and since there is not really any ventilation (except when i leave the cockpit locker open)it can get very hot in there.
I read somewhere that the colder( the fresher) the air is for the intake, the better the performance and i might gain more power too apparently.
The actual exhaust is already equiped with a muffler and exhaust silencer so that is not really the issue.
Would i t be wise to put some kind of a hose to the air intake so it takes the air from outside?
Can someone throw a bit light on this please.

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Old 08-07-2010, 17:34   #2
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You could try extending it, but unless you soundproof the hose you will probably still hear the popping. Slainte!

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Old 08-07-2010, 18:19   #3
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It sounds like you are trying to quiet down the engine and get a little more power while you are at it. Unfortunately, I don't think it will make a significant different in the end although you could do a pretty simple test and check it.

The sound in a diesel comes from many places, one of which is the air intake. On a naturally aspirated engine like you have, relatively little sound comes from the air intake, a lot more comes from the head, block and the exhaust. Even extending the air intake won't help that much since the actual pipe will transmit sound so it would need to have insulation on it.

The reason that people try to use cold air intakes is that the air is denser so they can get more of it into the cylinder at a given pressure. This is a really big deal for very high performance engines where they are trying to force as much air into the cylinder as possible so that they can burn the most fuel possible. Unlike gassers, diesels are fuel throttled not air throttled so unless you are overfueling, it won't make a difference.

Two things to worry about: Make sure that you are not causing a restriction to the intake, it will make everything worse rather than better. Also, make sure that you don't put the intake somewhere that a rogue wave could submerse it.
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Old 08-07-2010, 18:41   #4
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I would put in a fresh air duct but duct it down towards the bottom of the engine. The engine combustion air will then cause a circulation of air in the engine compartment and should reduce the temp. some. If you want to reduce the temp in the engine room more, then add an exhaust duct from near the top of the engine room with an exhaust fan. Make sure the intake duct is larger than the exhaust duct though.

That doesn't do anything for noise. Silencing noise is a very complicated business.
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Old 10-07-2010, 03:14   #5
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Thanks all. i put a 1m leftover of the Eberspacher heating exhaust- insulated for heat - that was flying around in one of the bilges and put fibreglass around it and made a hole underneath cockpit locker for air intake. Than came up with the ingeniuos idea of going to the car scrapyard and took the insulation sheet from under the bonnet of a 2 Mercedes cars (fits nicely with name of boat), chopped it all up and screwed it against the 'engine room wall'.
The popping noise of the air intake and the sound of the engine has been drastically reduced and i had it running for about an hour and temperature inside was ok.
its better to have a full bottle of rum in front of me than a full frontal lobotomy...
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