Air Intake Filter and Silencer

[jzuk]

On my still kinda new to me O'Day 35 I've had a fairly large ToDo list. I'm now at the point where I need to (and time to) replace the stock (and original) air filter.

I've seen the simple K&N filter replacement that the Compass Marine site wrote up. I like it, but wondering about one step further. If I make a simple air silencer (like on car air takes), and upsizing the filter a touch to maintain air flow.

In the upcoming year I hope to addresse engine compartment ventilation and possible improvements to sound insulation.

Not a lot of sound comes through the air intake, but every but helps. If I can minimize this sound, I hope that the other future projects could result in a much quieter running engine.

So anyone try to make an air intake silencer?
If not, I will take pics. Though it is sailing season and I would not hold my breath on when they will be posted here.

 

[Stu Jackson]

What engine? Until you answer this one, how can we help?

 

[jzuk]

Aww swear I had typed Universal M25XP (D950 Kubota block).
Did find a write up in the Catalina section, lot of good info on this and the M25 engine over there. I see you even posted in this thread.
http://forums.oday.sailboatowners.com/showthread.php?p=1079687&highlight=Air silencer

Tomorrow I'll swing by a Kubota dealer and check on part availability.
Looks like there filter housing deals with the sound issues, so I may not have to re-invent the wheel.

 

[Stu Jackson]

jz, always good to go to Kubota first. As far as sound is concerned, I still have difficulty, after 17 years of owning a boat with a diesel engine, understanding how anyone could believe an air intake could solve any engine "sound" issues. Diesels make noise. They need to be "open" to the cabin for air intake (unless you have a tricky big sophisticated super yacht with a truly separate "engine room" with proper ventilation). Sound travels through air. Vibration is a completely different thing, and engine mounts & proper alignment deal with that. An air filter called a "silencer", to me, is an oxymoron.

Good luck anyway. I have a "new style" air filter, new circa 1998 for Universal, on our M25. It's the older filter upgraded by Universal with a foam pad around it. Foam doesn't kill sound, nor would a K&N air filter, since they're made to allow air in, and air, well, transmits sound, right?

 

[Richard19068]

jz, always good to go to Kubota first. As far as sound is concerned, I still have difficulty, after 17 years of owning a boat with a diesel engine, understanding how anyone could believe an air intake could solve any engine "sound" issues. Diesels make noise. They need to be "open" to the cabin for air intake (unless you have a tricky big sophisticated super yacht with a truly separate "engine room" with proper ventilation). Sound travels through air. Vibration is a completely different thing, and engine mounts & proper alignment deal with that. An air filter called a "silencer", to me, is an oxymoron.

Good luck anyway. I have a "new style" air filter, new circa 1998 for Universal, on our M25. It's the older filter upgraded by Universal with a foam pad around it. Foam doesn't kill sound, nor would a K&N air filter, since they're made to allow air in, and air, well, transmits sound, right?

I don't know anything about a silencer but I know the K&N filter I use on my M-18 makes a lot more noise than the stock filter. I was surprised by that.

 

[Stu Jackson]

I don't know anything about a silencer but I know the K&N filter I use on my M-18 makes a lot more noise than the stock filter. I was surprised by that.

Richard, excuse me for nitpicking, but perhaps what you really meant was that the K&N filter allows more engine noise to get out. Filters don't make the noise, the engine does.

Sorry if that's too picky on my part, but we don't want any newbies getting the wrong impression.

 

[centerline]

there is some info about air velocity noise in this link here...

it does create some noise, but its the engine vibration and rattle that creates the bulk of the racket
if the engine is fitted with an enclosed filter housing, there is very little improvement you can make on if it has the stock filter, but if it is the open type filter without a housing then yes, you can make a considerable difference in the velocity noise by enclosing the filter....

the intake holes thru the housing to the filter should enter from the bottom of the housing, rather than from the sides for the quietest installation.

the velocity noise from a small displacement engine such as yours is very small in relation to the other noises the engine can make, and usually peaks out only during WOT operation under load....

but with a big bore engine, its different. the velocity noise can actually drown out the other noises of the engine, especially when fitted with devices that help with getting maximum, unrestricted airflow to the air intake port.

 

[Richard19068]

Richard, excuse me for nitpicking, but perhaps what you really meant was that the K&N filter allows more engine noise to get out. Filters don't make the noise, the engine does.

Sorry if that's too picky on my part, but we don't want any newbies getting the wrong impression.

No problem Stu. Clarity is good. I don't know what makes the noise. It sounds like the noise of the air rushing through the filter. The volume of the air sucking noise is just louder with the K&N filter than the stock filter. So much so that I thought about going back to the stock filter.

 

[jzuk]

Its nice having friends with access to odd parts.
Some nice 2" hose, 2" stainless elbow, parts to adapt to 1 3/4, and a really nice air filter.
Phone pics are bit to dark and not sure how to post picks here yet.

I attached 2" hose up and back, so the air filter is near the batteries. The slightly larger 2" hose should help with the air pressure changes of the valve opening and closing. The filter being back should be bit cooler.

A decibel app said that without anything (pretty close to stock filter) was close to 90 and with the new filter and hose 80 decibels at the galley. Kinda noticeable and a good change since I needed to change the air filter anyways.

 

[Panta Rei]

Its nice having friends with access to odd parts.
Some nice 2" hose, 2" stainless elbow, parts to adapt to 1 3/4, and a really nice air filter.
Phone pics are bit to dark and not sure how to post picks here yet.

I attached 2" hose up and back, so the air filter is near the batteries. The slightly larger 2" hose should help with the air pressure changes of the valve opening and closing. The filter being back should be bit cooler.

A decibel app said that without anything (pretty close to stock filter) was close to 90 and with the new filter and hose 80 decibels at the galley. Kinda noticeable and a good change since I needed to change the air filter anyways.

As you noted, Air intakes do make a lot of noise. I installed a Walker Air sep closed crankcase system on my 4 cylinder Kabota . Its primary function is to create a vacuum in the crankcase and direct any blowby back into the intake. It has a built-in intake silencer. Best $350 I spent on the boat. The engine does not leak a drop of oil since the crankcase has a vacuum. There is absolutely no fumes from any crankcase venting, and the engine is much quieter.

Other things I did the quiet the engine was replacing the old foam with real sound barrier inside the engine room. Sealed it up much better. Replaced the engine mounts and most importantly for the vibrations throughout the boat, I had the engine shaft aligned as precise as I could measure it.

Prior to the alignment, Strong vibrations would go through the boat at certain RPMs. Now the vibrations are much less and consistent over the RPM range.
I also added a axial fan to cool the engine compartment when the engine is not running. I used the same fan that is used to vent gas powered runabouts. The thing is so noisy I use it only if we are off the boat for a while. It does cool down the engine room but it must take hours for a 500 lb engine to cool down. It's a good reason to hit the bar while the fan is on.

It's very important to seal up the engine room air tight with the exception of the place were the air is designed to come into the engine room (generally through the bilge) The engine is a very good air pump and pumps enough air through the engine room to keep things cool while it is running. I thought the Axial fan would be a good way to cool the engine down after long periods of motoring but I did not take into account how slowly the heavy engine cools down.
This whole issue is very important on the O'day 39 as there sleeping cabins on each side of the engine room (box like compartment).

We took a trip across Lake Superior and had to motor most of the way. The aft cabins were warm toasty the whole night. It's 40 degs at nigh in mid July.
We baked a lot of cookies to keep the rest of the boat warm.

I would replace the axial fan with a squirrel cage fan if I was in a warmer climate.

 

[jzuk]

Thanks Panta Rei.

I realigned the propeller shaft this spring and that helped a lot, was too low through out the log. Was a bit rushed as some other repairs became needed, and I was one of the 'last out so first in' group. I'll check again the condition of the engine mounts, also think of propeller shaft coupling options.

In the spring I changed the vent for the crank case, and now I wil have to adjust for the new filter. i could not stand the oily crap in the bilge from the old crankcase vent. I'll check out the Walker air separator, as I presently just repurposed my old Graco fuel filter for that.

I'll keep in mind you Axil fan comment. The engine running temp seems to be good. My thought is to not cool the engine, but to help the air cooled refrigeration unit which is in the engine compartment right above the hot water tank (wish th PO had bought the water cooled compressor).

I'm on southern Georgian Bay, not nearly as cool as Superior in July. Guess after this is all sorted we can future out heaters.

 

[jviss]

I installed a Walker Air sep closed crankcase system on my 4 cylinder Kabota .

I know this is an old thread, but I came upon it while searching for noise reduction techniques and materials.

May I ask the model number of the kit you installed?

Thanks,

jv

 

[Panta Rei]

I know this is an old thread, but I came upon it while searching for noise reduction techniques and materials.

May I ask the model number of the kit you installed?

Thanks,

jv

https://www.walkerairsep.com/product_detail.asp?id=564
This unit is intended to be used on gen sets but as the web page states, it can also be used on small marine propulsion engines. My engine in 44 hp an the unit works great. Never oil in the bilge.

 

[jviss]

Thank you!