Engine breather filters

[998automan]

Hi, I am looking for opinions on the merits (or otherwise) of using an engine breather filter rather than the original system on my car of connecting the outlet from the tappet cover to the air filter box via a pipe. Is there any benefit to stopping the dirty air going back into the engine (other than not making a mess of the air filter). If this is worth doing where is the best mounting point to minimize the smoke/smell from entering the cabin? Cheers all.    

[Stu]

Mine connects onto the carb (HS4). I thought about terminating it to a pipe filter but coudn't see any benefit. The last part of your post is the other reason I've left it as factory.

[hbroodryk]

Hi

I have the same question. I am planning on using a conical K&N filter which currently has no means for connecting the breather to it. I could always drill a hole and plumb in a bit of tubing to get around this, but I don't really want to...

I am using a "catch-tank" with a filter on the end of that on my 2l twin cam Fiat engine (in a Lada Niva) which is OK, but it still emits a bit smoke once the engine is warm. I have run a pipe all the way to the front of the engine bay for the outlet and I have never noticed any smell in the cabin at all, not even in very slow traffic with the windows and the sunroof open. I am toying with the idea of running a tube down to the inside rear of the left wheel arch and putting a small tank and filter combo in there. I will need to check the space though and make some form of splash-guard to protect it from spray.

Regards
Hannes

[998automan]

Thanks guys, yes you are right Stu. After a bit of research it seems as if mine has been connected up to the air filter box by the previous owner and it is not how it was originally meant to be so I have ordered the correct pipe from mini spares. Does anyone know what the outlet from the air filter housing is for/should be connected to?

[wimfournier]

The outlet (inlet) to the airfilter housing was used in the beginning. But the oil fumes polluted the paper air filter, so they decided to bring the tube to the foot of the carburetor itself.
There is one point about carter ventilation that you must keep in mind.
The suction on the carter ventilation breather brings with it, that there is a slight vacuum in the carter in stead of a slight pressure over atmospheric pressure. So the oil seals at the cranck and differential are helped to keep the oil inside. When you don't use the positive carter ventilation in a proper way, the oil seals have a harder job to do. And you can see that by the oil that is spilled and contaminating your engine and gearbox and the inner sides of your motorroom. All the oil on the outside of the engine and box means lesser cooling. So the cooling system has a harder job to cope with the heat of the engine.

[998automan]

Thanks, that makes sense re the air filter. Can you clarify what you mean by carter ventilation? Also do I need to block the air filter box inlet if I am no longer using this to vent to the tappet cover?

[wimfournier]

Sorry, the word is 'crankcase', not carter.
No, the stub at the air filter house you can leave as it is. It is 'outside' the actual filter, so, no harm is done.

[richard1]

The crankcase of the engine requires ventilation to compensate for the pressure changes from acceleration, where some gases pass the rings, and deceleration, where a vacuum is created. Also just absorbs the variations from pistons going up and down. The engine really likes a slight vacuum in the crankcase to work at its best.

In the old days, there was just a road draft tube (as on my 1960 Corvair). It is sort of ventilated under the car, presenting a dangerous situation when stopped, and not really helping much. The venturi action on the road (speed) helped pull out those gasses.

So in the 60's, someone figured out that if you let the intake air be what pulls the vacuum with venturi action, there would always be a slight vacuum. The first systems just had a small restriction installed in a tube from the top of the engine to the air filter. As mentioned, this dirtied filters, so in general this inlet has been moved to below the filter. This process lets these gases be burned, presenting cleaner/safer air around the car, all going through the exhaust pipe.

But in the process the manufacturers also figured out that it was not good to have that open when you were decelerating, as that would draw additional air in through that port (being unfiltered if before the filter). So the PCV valve, that was really just an orifice, was changed to an orifice with a one-way valve. It should let air move from the crankcase to the intake, but not the reverse.

If the PCV gets clogged, you can see a dramatic increase in oil consumption. Just venting it to a little filter in the engine compartment does not draw a vacuum under any circumstances, although I've seen it done on many conversions to conical filters.

Will disconnecting it kill the engine - No. But it will dirty your oil more and in theory slightly reduce performance (probably need a dynamometer to prove that). You will also fail inspections in some countries/states/cities, and create a cloud of dangerous gas around your car that can creep into the cabin where the cables or tubes pass through the firewall.

[mra-minis]

The crankcase ventilation via carburettor has one major draw back, oil in your fuel air mixture will weaken the mix and lower your power output, venting to atmosphere is fine unless you are dropping oil and then you will as you do in most racing series need a catch tank.

to recap there is nothing good about adding oil to your mixture...

The only good thing is it burns the fumes...

[notamini]

I put a K&N conical on a '93 Honda Del Sol. The aluminium pipe which came with the kit had a small diameter fitting on the side between the intake and filter. Engine was multi-port. I don't know if this makes any difference. I just wanted to say, yes, K&N does have this available, obviously.

[wimfournier]

The proper use of these filters was meant to clear the air that is inhaled into the crankcase on racing engines that use a huge 'catch tank' to separate as much as possible oil from the air that is sucked out of the crankcase by the 'positive crankcase ventilation' system. There for the catch tank was connected with a tube to the foot of the carburettor, so that there was use of the strong vacuüm that you get when you take your foot from the throttle pedal. At that moment the catch tank is sucked fiercely so that a lot of fume gets into the burning chambres of the cilinders. The oil that comes with the air is lubricating the cilinderwalls. The stream of relatively cold air from outside is cooling the engine inside. With the throttle down again there is only a week vacuüm, only a little air from the catchtank reaching the burning chambers. Doing little harm to the octane caracter of the fuel.
When you disconnect the crankcase ventilation and put an airfilter on the tube you are doing something stupid. Or is it aimed at lessening poluting the surrounding air?

[mra-minis]

Can you show us where you got your information from please Wimfournier ?

[wimfournier]

No, Martin, I'm sorry. What I wrote is my understanding of the matter after years of reading articles on the internet. "How come" is the question I ask since my childhood. And reading .. 'the art of motor maintenance'. And, because of in racing you find the ultimate experiance of motor management I reed everything where I can lay my hand on in the subject.
So I'm always open for rectification when I'm wrong.

[mra-minis]

Long before filters were fitted to catch tanks, these filters originally had been fitted to motorbike engines to filter air to the combustion chambers...

Anything other than Oxygen and fuel mixture weakens the mixture, hence why N2O or Nitrous Oxide works so well because the oxygen content is much higher than the air we breathe. So any race engine that feeds the exhaust back into the inlet was going to lose power, modern EGR systems are designed and controlled differently.

By disconnecting the breather system from the inlet system you are cleaning the mixture to the engine, lessening the possibility of pre-ignition. The filter stops dirt from entering the crankcase and filters the gases escaping the crankcase, although the filtering is not as good as burning in the cylinders.

The cylinders of a diesel are lubricated by oil from below and diesel in the combustion chamber, although any oil getting in to a diesel will actually give you more power, in a lot of these cases the engine would be destroyed as it often meant it was sucking up oil past the rings, usually the engine would simply rev and rev till destruction.... look up on google vids for "diesel sucking sump oil" there are loads of vids with dramatic events.
However on a petrol the top doesn't require much lubrication at the honing marks in the bore allow a very tiny bit of oil to pass to the top ring from the sump.

By fitting a filter to atmosphere on your breather system you are adding a little to the pollutants in the air, however as it is oil based it will sink to the ground very quickly.

So there are positives and negatives, if you are going for the maximum performance then remove the breather system from your carburettor, if not then spend your money elsewhere ... like on one of my new shiny aluminium oil filter bowls :-)

[Stu]

Right. Armed with that detailed information I'm going to take the breather pipe off my carb and pop a filter on it instead.

I'm hoping for a power increase on my lil ole 850 Martin. What do you recon, 0.2 bhp

Seriously though, I assume capping off the redundant pipe on the carb is sufficient after the bypass? 

I almost didn't notice the discreet plug there Martin  do you have any to view??

[mra-minis]

Lol yeah, about 0.2bhp downhill .... what plug ;-) I have no idea how to add photo's on here...

I should add that pre-ignition is a big power killer, so removing it means you can run a higher advance

[Stu]

Great advice. Thanks Guru