Diesel intake noise reduction

Discussion in 'Diesel Engines' started by goodwilltoall, May 26, 2019.

  1. goodwilltoall
    Joined: Jul 2010
    Posts: 814
    Likes: 20, Points: 18, Legacy Rep: 31
    Location: nation of Ohio

    goodwilltoall Senior Member

    I have a 30hp diesel engine that makes a lot of noise at air intake. The intake is round at 1.5" (38mm), my plan is to connect a 2.0" (ID) rigid rubber hose of 5' (1.5meter) length with single loop above deck. There is plenty of exhaust ventilation

    Question: Is that enough air into engine area or should there be additional area for air intake
     
  2. BlueBell
    Joined: May 2017
    Posts: 749
    Likes: 76, Points: 28
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Sounds like a reasonable modification.
    How will you measure the outcome?
     
  3. Yellowjacket
    Joined: May 2009
    Posts: 603
    Likes: 85, Points: 28, Legacy Rep: 447
    Location: Landlocked...

    Yellowjacket Senior Member

    Adding tube length won't help. The acoustic pulses will just keep traveling back and forth in the tube and it will still be noisy.

    You need an airbox.

    A proper acoustically shaped airbox will kill the noise.

    Basically you want to have the pulses go into the box and there is a tube in the box that acts as a "one way valve".. Air goes in freely, but noise pulses don't come out.

    Here is one for a smaller engine that I've used with great success on a 10 hp 2 stroke motor that had inlet noise that was painful to be near. Once this was added the noise was totally gone. I did line the inside with acoustic foam 1/8 of an inch thick that was a "peel and stick" foam that I bought from Mc Master Carr.

    153. W850/1MR Mini Rok Plastic Air Box https://cometkartsales.com/153.-W850-1MR-Air-Filter.html

    You may need a bigger box, depending on the power of the diesel that you're trying to quiet. The intake of 2 stroke was exactly the same size as a shop vac hose (about 1.75 inches so it may be close to what you need or you could use 2 of them, but there are other air boxes for go-kart racing that would likely work very well in your case.
    Without an airbox you're just wasting your time trying to make the intake quiet.
     
    BlueBell likes this.
  4. goodwilltoall
    Joined: Jul 2010
    Posts: 814
    Likes: 20, Points: 18, Legacy Rep: 31
    Location: nation of Ohio

    goodwilltoall Senior Member

    Thx Yellowjacket, I will most likely give that a try but will still need close to a 5' run of hose to get it above deck and then also run a secondary hose to bottom of engine for additional air.

    This is the intake cover that I will attach to
     

    Attached Files:

  5. Yellowjacket
    Joined: May 2009
    Posts: 603
    Likes: 85, Points: 28, Legacy Rep: 447
    Location: Landlocked...

    Yellowjacket Senior Member

    How many HP is the engine? What displacement and what RPM? If you use an airbox you can just connect it to your inlet with a short length of shop vac hose, or even just put it right on the inlet. We had to use an adapter to neck the air box down to the size of our throttle body. We used a connector made by "Shop Vac" that adapted the hose to airbox rubber element. That particular airbox also has an internal filter that also helps cut the noise. It's a foam filter that has virtually no restriction. If you suck the air from the area around the engine it will cool the engine room by sucking warm air out of the room. I would not worry about trying to get the air inlet out of the engine room.
     
  6. goodwilltoall
    Joined: Jul 2010
    Posts: 814
    Likes: 20, Points: 18, Legacy Rep: 31
    Location: nation of Ohio

    goodwilltoall Senior Member

    That makes sense, a short hose to the airbox within the engine room but still have a baffled air inlet for the engine room as a whole.

    The engine is a Sabb 30Hp, 1900RPM with max torque around 1450RPM, 2Cyl, boat displacement 13,500#. I would go ahead and order airbox but it seems small being used for 10Hp go carts. Website didn't have bigger sizes and very little info
     
    Last edited: May 30, 2019
  7. Yellowjacket
    Joined: May 2009
    Posts: 603
    Likes: 85, Points: 28, Legacy Rep: 447
    Location: Landlocked...

    Yellowjacket Senior Member

    by displacement I meant cubic inches of engine displacement... You can figure out the approximate airflow that the engine requires by multiplying half the displacement by the speed and using a volumetric efficiency of about 90% for a low speed engine like this.

    But yes that box is probably a bit too small for your 30 hp diesel. We've used it on engines up to about 15 hp and it worked fine. An automotive airbox is going to be too big and likely won't muffle the noise very much.

    If you google go kart airboxes you will find many with two 29 or 30 mm tubes. Those boxes will work fine for your application, two 29 mm inlets are much larger in area than your single 35 mm inlet so you won't be restricting your inlet flow. Some of these airboxes have an internal filter element. Some do not. If you look at most of these boxes, including the first one I linked to, they use an angled "inlet rubber" fitting on the inlet. This rubber adapter is about 2.5 inches in diameter. You can buy an foam air filter that replaces that inlet adapter. They look just like that angled adapter but with a foam head that is now in the airbox. These have virtually no restriction and they reduce the noise significantly. A shop vac adapter will fit right into that adapter/filter and will let you use shop vac hose to connect with your inlet. The adapter even has a bellmouth shape inside for low losses. The large inlet adapter will also let you reach in and put peel and stick foam inside the box to reduce reverberation. Any one of those 29 or bigger airboxes will work just fine for your application. These boxes are specifically designed to reduce inlet noise from 2 stroke motors that are notoriously loud. We were amazed how well the box we had worked to kill the inlet noise of our engines. You can get these boxes for between 50 and $100 so that's pretty inexpensive given what you pay for most things in marine environment.
     
    BlueBell likes this.
  8. goodwilltoall
    Joined: Jul 2010
    Posts: 814
    Likes: 20, Points: 18, Legacy Rep: 31
    Location: nation of Ohio

    goodwilltoall Senior Member

    I talked to Comet salesman and he said unit linked above would be to small he recommended this unit which is even cheaper priced
     

    Attached Files:

  9. goodwilltoall
    Joined: Jul 2010
    Posts: 814
    Likes: 20, Points: 18, Legacy Rep: 31
    Location: nation of Ohio

    goodwilltoall Senior Member

    Also stopped at Duetz/Yanmar dealership and they have this air filter set up but I wonder if it would significantly reduce noise level of intake, made for yanmar diesel however not sure if its for their generator unit.
     

    Attached Files:

  10. Yellowjacket
    Joined: May 2009
    Posts: 603
    Likes: 85, Points: 28, Legacy Rep: 447
    Location: Landlocked...

    Yellowjacket Senior Member

    Because of noise regulations the 2 stroke inlet silencers are particularly effective. I would add the air filter that replaces the intake rubber adaptor and go with that. The Yanmar unit may or may not be that effective, you just don't know.
     
  11. goodwilltoall
    Joined: Jul 2010
    Posts: 814
    Likes: 20, Points: 18, Legacy Rep: 31
    Location: nation of Ohio

    goodwilltoall Senior Member

    I trust those 2 stroke intake silencers work however openings of 25mm (1") are too small, intake at engine is 44mm (1.75") and that is minimum I would install.

    Another issue is some call them air filters, airboxs, pre intake but hardly anyone calls them for purpose I intend to use them for "intake silencer"
     
  12. Yellowjacket
    Joined: May 2009
    Posts: 603
    Likes: 85, Points: 28, Legacy Rep: 447
    Location: Landlocked...

    Yellowjacket Senior Member

    Two 31 mm intakes have the virtually the same area as your 44 mm intake horn. 1520 mm sq vs 1509... A box with two 30 mm intakes will work fine. The purpose of those boxes is to reduce intake noise. The racers don't care about air cleaning, they rebuild so often it doesn't matter. The express purpose is to suppress the intake noise because there are regulations in Europe and the USA that require intake silencing. Karts used to have open exhaust and intakes and the noise was horrendous. They first put on exhaust silencers and that helped some, but they found that they had to attack the inlet noise because the closing of the reed valves caused so much intake noise. Our intake without a silencer had noise levels of over 90 dba. Adding the airbox and putting the cover on the boat dropped it do 73 dba and most of that noise remaining was exhaust noise.... Look for boxes that have two 30mm intakes or larger and you'll be amazed how well they will work in this application. I would look for a connecting hose of at least 2 inches in diameter and keep it short and then get a vac adaptor to get from the inlet to the hose. You can get silicone hoses connectors for turbo systems that will go from your 1.75 inlet up to a 2 inch connector.
     

  13. goodwilltoall
    Joined: Jul 2010
    Posts: 814
    Likes: 20, Points: 18, Legacy Rep: 31
    Location: nation of Ohio

    goodwilltoall Senior Member

    Thx Yellowjacket,
    I will try that, about same price as the yanmar filter for the 2 airbox you mention however, those are 22mm and cutting it close, most likely have to search for double 30mm.

    I will let you know how it works after installation
     
    Last edited: Jun 4, 2019
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.