Holes in air boxes

Engines and Engine Systems
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Peter Connan
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Holes in air boxes

Post by Peter Connan » 12 Feb 2018 10:54

This comes from a Whatsap group discussion with some friends.

The factory air-box from the ZD30 (and probably others as well, i haven't looked) has a 4mm hole in the bottom, outside the filter.

The questions are what it's for and what disadvantages it may have, especially regarding fording.

My opinion is that the main advantage is to let out water and dust. Air always has some water in it. How much depends on atmospheric conditions.
This water will be shed under certain conditions, but typically will only cause issues if the water is not absorbed in the air. Under heavy rain, this can happen. The faster air moves, the more water it will carry.

The area in the air box where the hole is, is also the area where air velocities are lowest, and thus where the most water will "drop out". Also, any water swirling around in here will tend do drag whatever dust is lying on the bottom with it.

As far as wading is concerned, i doubt enough water can enter through such a small hole to cause engine damage as long as the engine is running. And if you stall the engine during the crossing, the exhaust is much more of a problem.

However, if one is really concerned, it's easy enough just to plug it temporarily with duct tape or prestic.
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Re: Holes in air boxes

Post by SCUBA Patrol » 12 Feb 2018 11:13

Peter,

I agree with you that small hole is for water that does enter the system to drain out. The hole usually have a rubber seal that only let water out and not in, had one on the Donaldson filter of the Sani have not looked at the Patrol's? This should keep out water and dust entering the hole from the outside.

If you are concerned of water entering during a water crossing the prestick/duct tape covering the hole will work in my opinion.

PS. if you need to do that for a water crossing turn around and search for the bridge! Will be more exciting that stressing about water entering the engine.
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Re: Holes in air boxes

Post by Peter Connan » 12 Feb 2018 12:45

The ZD30 filter housin I examined did not have any one-way-valve arrangement.

The pre-filter on the petrol Y60 does have a rubber one-way device like you describe, but the whole is much bigger, probably in the order of 20-25mm.

I also feel that if you need to ford that deep for that long you should probably have bought a submarine.
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Re: Holes in air boxes

Post by SCUBA Patrol » 12 Feb 2018 12:50

Correct on that Diameter, I'll check my 30Di. Have not looked at it in that detail..... yet :confused:
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Re: Holes in air boxes

Post by JoshJ » 12 Feb 2018 13:53

I agree that water that deep should rather be avoided. It comes with a whole lot of other issues.

On the whole. If my airbox doesnt have one I wont make one. I dont see how that 4mm hole can aid with any of the above while the engine is running. :mytwocents:
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Re: Holes in air boxes

Post by SCUBA Patrol » 12 Feb 2018 14:05

I agree Josh, and it does not work while driving in a snow storm with a snorkel on!!! It just drives the snow down to the filter element, that gets wet and blocks....
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Re: Holes in air boxes

Post by Peter Connan » 12 Feb 2018 17:00

This is what it looks like, seen from outside.
IMG-20180212-WA0006.jpg
I am prett6 sure that, at low engine speeds, this hole will ne able to drain water. At higher engine speeds, probably not.

For snow, i have no idea. I avoid the stuff wherever possible.
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