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I have recently fabricated a new airbox for my td42t with a 4 inch snorkel, I have run new breathers for the diffs and crankcase into the box aswell but I have been told this morning that this is a bad idea...apparently it can cause vacuum and suck water and dirt through the seals and even suck the oil out of the diffs and case...the air box is pretty free flowing and I couldnt see this causing a hole lot of vacuum but I need to double check before I run it and use the truck, can anyone help me with some advice.....thanks team I have a picture below of my set up....
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It won't suck the oil up and out, but it will make definitely cause the pressure to be low in the driveline components. Low pressure when, say, entering a creek crossing = more likely to suck water in past the seals.

Don't do it.
 

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How are others doing this then, I have seen other boxs and heard of people having all there breathers in the main air box, I dont like the idea of having them on the firewall or engine bay as they are still able to suck up crap... iv seen another one were they hook them up to the snorkel....
 

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How are others doing this then, I have seen other boxs and heard of people having all there breathers in the main air box, I dont like the idea of having them on the firewall or engine bay as they are still able to suck up crap... iv seen another one were they hook them up to the snorkel....
I've seen breathers plumbed into the air intake system too -- it doesn't make it a good idea. If (like most people, including me) you put a filter on the top of the breather line, any air breathed into the system will be just as filtered as if it was connected to the airbox after the main engine filter.

Hell, from the factory the breathers aren't filtered at all, so I doubt it's a huge issue.
 

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It's not really about filtering the air for me it's more about water proofing and trying to keep it tidy ( sorta tidy ) I just like the idea of all the breathers being in a common spot..and i think it looks pretty sweet like that haha, cheers for the info so far this is something i didnt even consider while making the box
 

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I've done pretty much the same as you. Not for the filtering as you said but to stop water getting into the breather lines in water crossings. I did think about this but I cannot see it causing an issue, a 4" snorkel is a huge opening I find it hard to believe that there would be enough vacuum to suck water past the driveline seals. Certainly not going to suck oil out of the gearbox or diffs that's just ridiculous. That's just my thoughts anyway. Been running my setup for a while with no issues. Happy to hear other thoughts
 

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wont suck the oil up but will create a vacuum in a component not designed to have a vacuum in it. Under certain conditions it will create a problem. I know my TD42T creates a fair amount of induction pressure when on boost and would rather not have my diffs and gearbox dealing with this vacuum
 

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The only way you could create a vacuum in the gearbox or diffs is if there was an obstruction somewhere between the snorkel intake and where the diff and gearbox breathers are venting to in mine and the op's case not even the air filter can act as an obstruction because they are venting BEFORE the air filter
 

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There is no possible way you will create a vacuum with this setup, ever so slightly reduce the pressure in the diffs etc yes, but you would have to be on full boost with a stonking big turbo to achieve anything like a low enough pressure to pull moisture past the seals. If that's how you drive then you deserve it.

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If you take the head off your snorkel and stick your hand over it, it will just about suck your hand in at idle if it's all sealed properly, let alone at bigger revs.

Sure it will only make a small difference, but the whole point of the breathers is to level out the very small difference in pressure with heat changes in the diff, it doesn't take much pressure to draw liquid past a seal that was not designed to have different air pressure on each side of it.

I put mine at the top of the engine bay with a small filter; seriously, if it gets water in it there, it's the LEAST of your problems, and by a hefty margin.
 

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Yes that's correct you feel and create a massive vacuum on your hand when you stick your hand over the snorkel because the outlet of the snorkel (in the air box) remains the same at 4" but the inlet goes from 4" to zero when the engine is trying to draw air which creates a vacuum. But when the snorkel is open and free of any obstructions where in inlet and outlet are the same diameter in this case 4" there is no vacuum there only air velocity.
 

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Velocity over a tube creates the ‘Venturi Effect’, which is a vacuum. Just saying.
 

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Venturi effect is created when there is a construction in a pipe. From the op's picture the air is not flowing over the outlet of the breathers so I don't think would create a veturi effect.

Fluid velocity in a tube is directly proportional to the area of the tube in this case the snorkel, the equation V1xA1=V2xA2 Can be applied and the velocity of the air at either end of the tube can be found by rearranging this equation. When you do this you quickly see that the velocity at one end of the tube is equal to the velocity at the other end multiplied by the radio of tube diammters. If the tube diameters are the same (which I assume they would be otherwise it would be a rubbish snorkel) then the ratio is 1 which means that the velocity at each end of the tube is equal if there is no restrictions. The relationship between pressure and velocity can be found by applying bernollis equation. Which is:
P1 X pgh1 X .5pV^2 = P2 X pgh2 X .5pV^2
This is basically pressure X potential energy1 X kinetic energy1 = pressure2 X potential enery2 X kinetic energy2
We just established that because the diameters are the same there cannot be a velocity difference so that can cancel out of the equation. Potential energy when talking about a gas, (in this case air in snorkel is insignificant and would only serve to reduce a vacuum as the inlet of the snorkel is higher than the outlet to the airbox), so we can cancel that which means there cannot be a pressure difference if the diameter is the same velocity is the same and potential energy is the same. Now you might say that there is some friction losses between the inlet and outlet of the snorkel but again that would be very insignificant when talking about air flowing through a tube with reasonable assumptions. Just because air is flowing through a tube doesn't mean there is a vacuum.

Addition: as a matter of interest I just booked a vacuum gauge to the fittings where my breathers are connected to the aribox and I cannot get the needle to budge or even twitch throughout the td42 rev range. Think of it this way, if you were to crank you garden hose on full bore with no nozzle or anything attached. Then hook up a pressure gauge perpendicular to the water flow, say 5cm back from where the water was coming out how much pressure would you expect to see on the gauge?... With no restriction on the end of the hose you would see zero right? Even though there is water flowing through the hose, same principle applies.

To me the math works out, vacuum gauge test checks out, and the personal experience checks out I've been running this for a long time. The op has made a really nice airbox it would be a pitty if he didn't use it.

Dunno just saying I guess....
 

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In the OP’s pic, there isn’t air flowing perpendicular to the breather outlets as per your argument, so I’m unsure what your point is.

The only possible way air will come in to the air box, is if the pressure on the turbo side is lower than the pressure on the snorkel side, (wait, what? That’s a vacuum!), and it will naturally want to equalize, I’m sure everyone agrees there. Looking at that pic, the inlet and breathers are all parallel. Obviously the bulk of the air will come through the snorkel, as intended, but to say there is NO vacuum in the breather pipes because it’s easier fit air to flow through the snorkel is borderline farcical. That defies physics.

No one is suggesting it would be a significant amount, but can you quantify whether or not, in a river crossing with operating temp diffs dunking in the drink, you rev the engine as the bottom is a bit slimey, with breathers copping a bit of vacuum to counteract the amount of air the diff tries to suck in, can you guarantee your diff seals will be no more likely to draw in some water and mud than they would if the breathers were exposed to atmospheric pressure at the top of the engine bay?
 

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Think of it this way, if you were to crank you garden hose on full bore with no nozzle or anything attached. Then hook up a pressure gauge perpendicular to the water flow, say 5cm back from where the water was coming out how much pressure would you expect to see on the gauge?... With no restriction on the end of the hose you would see zero right? Even though there is water flowing through the hose, same principle applies.
Hahaha! I had to check it wasn’t April 1st!!!

So water flowing in a hose, even with no restriction on the end, would exert no pressure on a perpendicular pressure gauge?

So you’re saying the water exerts NO PRESSURE on the sides of the hose?

Hmm.

Well in that case, we wouldn’t need the hose. The water would just continue indefinately in the same tubular shape, and the same direction (because it would defy gravity, which would exert equivalent force of 9.81m/s2 toward the center of the earth).

Likewise, you’re saying if I drilled a hole in the side of the hose, or for that matter 100 holes in the side of the hose, none of them would leak... Um, yes that’s what you’re saying because the water would exert zero force perpendicular to the flow direction.

Saturday night comedy at its finest! Great work 😂
 

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It can be proven using fluid dynamic principles and mathematics, the airbox and snorkel cannot support or maintain a vacuum with a 4" opening at the top of the snorkel not to mention the fact that when I unplug my gearbox and diff breathers and fit a vacuum gauge I am unable to get any reading whatso ever. Op doesn't have to take my advice it's up to him to decide.

The water in the hose thing was merely an illustration to show that just because water is flowing through the hose at the end does not mean that the hose is holding pressure near the point of discharge. Maybe not the best example as the water is much more susceptible to friction losses in the hose which creates a difference in velocity and therefore a difference in pressure. My point is that air flow and vacuum are not the same thing just because air is flowing through a tube or a snorkel does not necessarily mean that a vacuum is being held in that tube or snorkel.
 

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Well what makes the air come through the snorkel when the engine is operating? Magic????
 
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